diff --git a/src/main/java/org/openrewrite/github/DependabotEcosystemManifests.java b/src/main/java/org/openrewrite/github/DependabotEcosystemManifests.java
new file mode 100644
index 0000000..1891201
--- /dev/null
+++ b/src/main/java/org/openrewrite/github/DependabotEcosystemManifests.java
@@ -0,0 +1,96 @@
+/*
+ * Copyright 2025 the original author or authors.
+ * <p>
+ * Licensed under the Moderne Source Available License (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * <p>
+ * https://docs.moderne.io/licensing/moderne-source-available-license
+ * <p>
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.openrewrite.github;
+
+import org.jspecify.annotations.Nullable;
+
+import java.util.*;
+
+import static java.util.Arrays.asList;
+import static java.util.Collections.*;
+
+// Ecosystems absent from this map are deliberately left alone rather than mapped to a broader
+// pattern such as the whole directory, which would grant ownership beyond what Dependabot covered.
+final class DependabotEcosystemManifests {
+
+    static final String GITHUB_ACTIONS = "github-actions";
+
+    private static final Map<String, List<String>> MANIFESTS;
+
+    static {
+        Map<String, List<String>> manifests = new LinkedHashMap<>();
+        manifests.put("bundler", asList("Gemfile", "Gemfile.lock"));
+        manifests.put("cargo", asList("Cargo.toml", "Cargo.lock"));
+        manifests.put("composer", asList("composer.json", "composer.lock"));
+        manifests.put("devcontainers", asList(".devcontainer/devcontainer.json", ".devcontainer.json"));
+        manifests.put("docker", singletonList("Dockerfile"));
+        manifests.put("docker-compose", asList("docker-compose.yml", "docker-compose.yaml"));
+        manifests.put("elm", singletonList("elm.json"));
+        manifests.put("gitsubmodule", singletonList(".gitmodules"));
+        manifests.put("gomod", asList("go.mod", "go.sum"));
+        manifests.put("gradle", asList("build.gradle", "build.gradle.kts", "gradle/libs.versions.toml"));
+        manifests.put("helm", asList("Chart.yaml", "Chart.lock"));
+        manifests.put("maven", singletonList("pom.xml"));
+        manifests.put("mix", asList("mix.exs", "mix.lock"));
+        manifests.put("npm", asList("package.json", "package-lock.json", "yarn.lock", "pnpm-lock.yaml"));
+        manifests.put("nuget", asList("*.csproj", "packages.config"));
+        manifests.put("pip", asList("requirements.txt", "pyproject.toml", "Pipfile", "Pipfile.lock"));
+        manifests.put("pub", asList("pubspec.yaml", "pubspec.lock"));
+        manifests.put("swift", asList("Package.swift", "Package.resolved"));
+        manifests.put("terraform", singletonList("*.tf"));
+        manifests.put("uv", asList("pyproject.toml", "uv.lock"));
+        MANIFESTS = unmodifiableMap(manifests);
+    }
+
+    private DependabotEcosystemManifests() {
+    }
+
+    static boolean isKnown(@Nullable String ecosystem) {
+        return GITHUB_ACTIONS.equals(ecosystem) || MANIFESTS.containsKey(ecosystem);
+    }
+
+    static List<String> patternsFor(@Nullable String ecosystem, String directory) {
+        String prefix = normalizeDirectory(directory);
+        if (GITHUB_ACTIONS.equals(ecosystem)) {
+            // A non-root directory points at a composite action definition rather than the workflows
+            return "/".equals(prefix) ?
+                    singletonList("/.github/workflows/") :
+                    asList(prefix + "action.yml", prefix + "action.yaml");
+        }
+        List<String> manifests = MANIFESTS.get(ecosystem);
+        if (manifests == null) {
+            return emptyList();
+        }
+        List<String> patterns = new ArrayList<>(manifests.size());
+        for (String manifest : manifests) {
+            patterns.add(prefix + manifest);
+        }
+        return patterns;
+    }
+
+    // Dependabot directories are repository-root relative and not searched recursively, so they
+    // map onto CODEOWNERS patterns anchored with a leading slash
+    private static String normalizeDirectory(String directory) {
+        String trimmed = directory.trim();
+        while (trimmed.startsWith("/")) {
+            trimmed = trimmed.substring(1);
+        }
+        while (trimmed.endsWith("/")) {
+            trimmed = trimmed.substring(0, trimmed.length() - 1);
+        }
+        return trimmed.isEmpty() ? "/" : "/" + trimmed + "/";
+    }
+}
diff --git a/src/main/java/org/openrewrite/github/ReplaceDependabotReviewersWithCodeowners.java b/src/main/java/org/openrewrite/github/ReplaceDependabotReviewersWithCodeowners.java
new file mode 100644
index 0000000..f9f204a
--- /dev/null
+++ b/src/main/java/org/openrewrite/github/ReplaceDependabotReviewersWithCodeowners.java
@@ -0,0 +1,311 @@
+/*
+ * Copyright 2025 the original author or authors.
+ * <p>
+ * Licensed under the Moderne Source Available License (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * <p>
+ * https://docs.moderne.io/licensing/moderne-source-available-license
+ * <p>
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.openrewrite.github;
+
+import lombok.EqualsAndHashCode;
+import lombok.Getter;
+import lombok.Value;
+import org.jspecify.annotations.Nullable;
+import org.openrewrite.*;
+import org.openrewrite.text.PlainText;
+import org.openrewrite.text.PlainTextParser;
+import org.openrewrite.yaml.DeleteKey;
+import org.openrewrite.yaml.YamlIsoVisitor;
+import org.openrewrite.yaml.tree.Yaml;
+
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.*;
+
+import static java.util.Arrays.asList;
+import static java.util.Collections.*;
+import static java.util.stream.Collectors.toList;
+
+@Value
+@EqualsAndHashCode(callSuper = false)
+public class ReplaceDependabotReviewersWithCodeowners extends ScanningRecipe<ReplaceDependabotReviewersWithCodeowners.Accumulator> {
+
+    private static final String DEFAULT_CODEOWNERS_PATH = ".github/CODEOWNERS";
+    private static final List<String> CODEOWNERS_PRECEDENCE =
+            unmodifiableList(asList(".github/CODEOWNERS", "CODEOWNERS", "docs/CODEOWNERS"));
+    private static final Set<String> CODEOWNERS_LOCATIONS =
+            unmodifiableSet(new LinkedHashSet<>(CODEOWNERS_PRECEDENCE));
+    private static final Set<String> DEPENDABOT_LOCATIONS = unmodifiableSet(new LinkedHashSet<>(
+            asList(".github/dependabot.yml", ".github/dependabot.yaml")));
+    private static final String HEADER = "# Reviewers migrated from the Dependabot configuration";
+
+    @Option(displayName = "`CODEOWNERS` path",
+            description = "Where to write the migrated reviewers when the repository does not have a " +
+                    "`CODEOWNERS` file yet. Defaults to `.github/CODEOWNERS`. When a `CODEOWNERS` file " +
+                    "already exists in any of the locations GitHub recognizes, that file is appended to " +
+                    "instead and this option is ignored.",
+            required = false,
+            example = "CODEOWNERS")
+    @Nullable
+    String codeownersPath;
+
+    String displayName = "Replace Dependabot `reviewers` with `CODEOWNERS`";
+
+    String description = "Replaces the [removed](https://github.blog/changelog/2025-04-29-dependabot-reviewers-configuration-option-being-replaced-by-code-owners/) " +
+            "`reviewers` option in `.github/dependabot.yml` with equivalent `CODEOWNERS` entries. Each " +
+            "reviewer is mapped onto the manifest files Dependabot updates for that `package-ecosystem` " +
+            "and `directory`, so ownership stays as narrow as the Dependabot configuration was. Update " +
+            "entries whose `package-ecosystem` has no known manifests are left untouched.";
+
+    Set<String> tags = unmodifiableSet(new LinkedHashSet<>(asList("dependabot", "dependencies", "github")));
+
+    @Override
+    public Accumulator getInitialValue(ExecutionContext ctx) {
+        return new Accumulator();
+    }
+
+    @Override
+    public TreeVisitor<?, ExecutionContext> getScanner(Accumulator acc) {
+        return new TreeVisitor<Tree, ExecutionContext>() {
+            @Override
+            public @Nullable Tree visit(@Nullable Tree tree, ExecutionContext ctx) {
+                if (!(tree instanceof SourceFile)) {
+                    return tree;
+                }
+                SourceFile sourceFile = (SourceFile) tree;
+                String path = normalize(sourceFile.getSourcePath());
+                if (CODEOWNERS_LOCATIONS.contains(path)) {
+                    acc.foundCodeowners(path, sourceFile);
+                } else if (DEPENDABOT_LOCATIONS.contains(path) && sourceFile instanceof Yaml.Documents) {
+                    new ReviewersScanner(acc).visit(sourceFile, ctx);
+                }
+                return tree;
+            }
+        };
+    }
+
+    @Override
+    public Collection<SourceFile> generate(Accumulator acc, ExecutionContext ctx) {
+        if (!acc.canMigrate() || acc.getExistingCodeowners() != null) {
+            return emptyList();
+        }
+        String path = codeownersPath == null ? DEFAULT_CODEOWNERS_PATH : codeownersPath;
+        String contents = HEADER + '\n' + String.join("\n", renderLines(acc.getOwnersByPattern())) + '\n';
+        return PlainTextParser.builder().build().parse(contents)
+                .map(created -> (SourceFile) created.withSourcePath(Paths.get(path)))
+                .collect(toList());
+    }
+
+    @Override
+    public TreeVisitor<?, ExecutionContext> getVisitor(Accumulator acc) {
+        if (!acc.canMigrate()) {
+            return TreeVisitor.noop();
+        }
+        return new TreeVisitor<Tree, ExecutionContext>() {
+            @Override
+            public @Nullable Tree visit(@Nullable Tree tree, ExecutionContext ctx) {
+                if (!(tree instanceof SourceFile)) {
+                    return tree;
+                }
+                SourceFile sourceFile = (SourceFile) tree;
+                if (DEPENDABOT_LOCATIONS.contains(normalize(sourceFile.getSourcePath())) && sourceFile instanceof Yaml.Documents) {
+                    String ecosystems = String.join("|", acc.getMigratedEcosystems());
+                    return new DeleteKey("$.updates[?(@.package-ecosystem =~ '(" + ecosystems + ")')].reviewers", null)
+                            .getVisitor().visitNonNull(sourceFile, ctx);
+                }
+                if (sourceFile instanceof PlainText && sourceFile.getSourcePath().equals(acc.getExistingCodeowners())) {
+                    return append((PlainText) sourceFile, acc.getOwnersByPattern());
+                }
+                return sourceFile;
+            }
+        };
+    }
+
+    private static PlainText append(PlainText codeowners, Map<String, Set<String>> ownersByPattern) {
+        String original = codeowners.getText();
+        String newline = original.contains("\r\n") ? "\r\n" : "\n";
+        String[] lines = original.split("\r?\n", -1);
+
+        // CODEOWNERS is last match wins, so a second line for a pattern would silently displace the
+        // owners already on the first; merge into that line instead to keep both sets of reviewers
+        Set<String> mergedPatterns = new HashSet<>();
+        boolean merged = false;
+        for (int i = 0; i < lines.length; i++) {
+            String trimmed = lines[i].trim();
+            if (trimmed.isEmpty() || trimmed.startsWith("#")) {
+                continue;
+            }
+            String[] tokens = trimmed.split("\\s+");
+            Set<String> owners = ownersByPattern.get(tokens[0]);
+            if (owners == null) {
+                continue;
+            }
+            mergedPatterns.add(tokens[0]);
+            Set<String> alreadyOwning = new HashSet<>(asList(tokens).subList(1, tokens.length));
+            List<String> missingOwners = owners.stream()
+                    .filter(owner -> !alreadyOwning.contains(owner))
+                    .collect(toList());
+            if (!missingOwners.isEmpty()) {
+                lines[i] = trimTrailing(lines[i]) + ' ' + String.join(" ", missingOwners);
+                merged = true;
+            }
+        }
+
+        Map<String, Set<String>> missing = new LinkedHashMap<>();
+        ownersByPattern.forEach((pattern, owners) -> {
+            if (!mergedPatterns.contains(pattern)) {
+                missing.put(pattern, owners);
+            }
+        });
+
+        String existing = String.join(newline, lines);
+        if (missing.isEmpty()) {
+            return merged ? codeowners.withText(existing) : codeowners;
+        }
+
+        StringBuilder text = new StringBuilder(existing);
+        if (!existing.isEmpty()) {
+            if (existing.charAt(existing.length() - 1) != '\n') {
+                text.append(newline);
+            }
+            text.append(newline);
+        }
+        text.append(HEADER);
+        for (String line : renderLines(missing)) {
+            text.append(newline).append(line);
+        }
+        // Match the trailing newline convention the file already used
+        if (existing.endsWith("\n")) {
+            text.append(newline);
+        }
+        return codeowners.withText(text.toString());
+    }
+
+    private static String trimTrailing(String line) {
+        int end = line.length();
+        while (end > 0 && Character.isWhitespace(line.charAt(end - 1))) {
+            end--;
+        }
+        return line.substring(0, end);
+    }
+
+    private static List<String> renderLines(Map<String, Set<String>> ownersByPattern) {
+        List<String> lines = new ArrayList<>(ownersByPattern.size());
+        ownersByPattern.forEach((pattern, owners) -> lines.add(pattern + ' ' + String.join(" ", owners)));
+        return lines;
+    }
+
+    private static String normalize(Path path) {
+        return path.toString().replace('\\', '/');
+    }
+
+    private static class ReviewersScanner extends YamlIsoVisitor<ExecutionContext> {
+        private final Accumulator acc;
+
+        private ReviewersScanner(Accumulator acc) {
+            this.acc = acc;
+        }
+
+        @Override
+        public Yaml.Mapping.Entry visitMappingEntry(Yaml.Mapping.Entry entry, ExecutionContext ctx) {
+            if ("updates".equals(entry.getKey().getValue()) && entry.getValue() instanceof Yaml.Sequence) {
+                for (Yaml.Sequence.Entry update : ((Yaml.Sequence) entry.getValue()).getEntries()) {
+                    if (update.getBlock() instanceof Yaml.Mapping) {
+                        collect((Yaml.Mapping) update.getBlock());
+                    }
+                }
+            }
+            return super.visitMappingEntry(entry, ctx);
+        }
+
+        private void collect(Yaml.Mapping update) {
+            List<String> reviewers = scalars(value(update, "reviewers"));
+            if (reviewers.isEmpty()) {
+                return;
+            }
+            String ecosystem = scalar(value(update, "package-ecosystem"));
+            if (!DependabotEcosystemManifests.isKnown(ecosystem)) {
+                return;
+            }
+
+            List<String> directories = scalars(value(update, "directories"));
+            if (directories.isEmpty()) {
+                String directory = scalar(value(update, "directory"));
+                directories = singletonList(directory == null ? "/" : directory);
+            }
+
+            for (String directory : directories) {
+                for (String pattern : DependabotEcosystemManifests.patternsFor(ecosystem, directory)) {
+                    Set<String> owners = acc.getOwnersByPattern().computeIfAbsent(pattern, p -> new LinkedHashSet<>());
+                    for (String reviewer : reviewers) {
+                        owners.add(reviewer.startsWith("@") ? reviewer : "@" + reviewer);
+                    }
+                }
+            }
+            acc.getMigratedEcosystems().add(ecosystem);
+        }
+
+        private static Yaml.@Nullable Block value(Yaml.Mapping mapping, String key) {
+            for (Yaml.Mapping.Entry entry : mapping.getEntries()) {
+                if (key.equals(entry.getKey().getValue())) {
+                    return entry.getValue();
+                }
+            }
+            return null;
+        }
+
+        private static @Nullable String scalar(Yaml.@Nullable Block block) {
+            return block instanceof Yaml.Scalar ? ((Yaml.Scalar) block).getValue() : null;
+        }
+
+        private static List<String> scalars(Yaml.@Nullable Block block) {
+            if (!(block instanceof Yaml.Sequence)) {
+                return emptyList();
+            }
+            List<String> values = new ArrayList<>();
+            for (Yaml.Sequence.Entry entry : ((Yaml.Sequence) block).getEntries()) {
+                String value = scalar(entry.getBlock());
+                if (value != null && !value.trim().isEmpty()) {
+                    values.add(value.trim());
+                }
+            }
+            return values;
+        }
+    }
+
+    @Getter
+    public static class Accumulator {
+        private final Map<String, Set<String>> ownersByPattern = new LinkedHashMap<>();
+        private final Set<String> migratedEcosystems = new LinkedHashSet<>();
+
+        private @Nullable Path existingCodeowners;
+        private int existingCodeownersPrecedence = Integer.MAX_VALUE;
+
+        // A CODEOWNERS not parsed as plain text cannot be appended to, and deleting the reviewers
+        // without recording them anywhere would lose the configuration
+        private boolean codeownersIsAppendable = true;
+
+        void foundCodeowners(String path, SourceFile sourceFile) {
+            // GitHub honors only one CODEOWNERS: .github wins over the root, which wins over docs
+            int precedence = CODEOWNERS_PRECEDENCE.indexOf(path);
+            if (precedence >= existingCodeownersPrecedence) {
+                return;
+            }
+            existingCodeownersPrecedence = precedence;
+            codeownersIsAppendable = sourceFile instanceof PlainText;
+            existingCodeowners = codeownersIsAppendable ? sourceFile.getSourcePath() : null;
+        }
+
+        boolean canMigrate() {
+            return !ownersByPattern.isEmpty() && codeownersIsAppendable;
+        }
+    }
+}
diff --git a/src/main/resources/META-INF/rewrite/recipes.csv b/src/main/resources/META-INF/rewrite/recipes.csv
index 73408e9..4dfd62f 100644
--- a/src/main/resources/META-INF/rewrite/recipes.csv
+++ b/src/main/resources/META-INF/rewrite/recipes.csv
@@ -20,6 +20,7 @@ maven,org.openrewrite.recipe:rewrite-github-actions,org.openrewrite.github.Prefe
 maven,org.openrewrite.recipe:rewrite-github-actions,org.openrewrite.github.RemoveAllCronTriggers,Remove all cron triggers,Removes all cron triggers from a workflow.,1,,GitHub Actions,,Recipes to perform [GitHub Actions](https://docs.github.com/en/actions) hygiene and migration tasks.,,
 maven,org.openrewrite.recipe:rewrite-github-actions,org.openrewrite.github.RemoveUnusedWorkflowDispatchInputs,Remove unused workflow dispatch inputs,Remove workflow_dispatch inputs that are not referenced anywhere in the workflow file.,1,,GitHub Actions,,Recipes to perform [GitHub Actions](https://docs.github.com/en/actions) hygiene and migration tasks.,,
 maven,org.openrewrite.recipe:rewrite-github-actions,org.openrewrite.github.RemoveWorkflowInputArgument,Remove workflow input argument,Remove a specific input argument from calls to a reusable workflow.,1,,GitHub Actions,,Recipes to perform [GitHub Actions](https://docs.github.com/en/actions) hygiene and migration tasks.,"[{""name"":""workflowReference"",""type"":""String"",""displayName"":""Workflow reference"",""description"":""The workflow reference to match (e.g., `org/repo/.github/workflows/myWorkflow.yml`)."",""example"":""org/repo/.github/workflows/myWorkflow.yml"",""required"":true},{""name"":""version"",""type"":""String"",""displayName"":""Version"",""description"":""The version of the workflow to match (e.g., `v1.2.3`)."",""example"":""v1.2.3"",""required"":true},{""name"":""inputArgumentName"",""type"":""String"",""displayName"":""Input argument name"",""description"":""The name of the input argument to remove."",""example"":""myInputToRemove"",""required"":true}]",
+maven,org.openrewrite.recipe:rewrite-github-actions,org.openrewrite.github.ReplaceDependabotReviewersWithCodeowners,Replace Dependabot `reviewers` with `CODEOWNERS`,"Replaces the [removed](https://github.blog/changelog/2025-04-29-dependabot-reviewers-configuration-option-being-replaced-by-code-owners/) `reviewers` option in `.github/dependabot.yml` with equivalent `CODEOWNERS` entries. Each reviewer is mapped onto the manifest files Dependabot updates for that `package-ecosystem` and `directory`, so ownership stays as narrow as the Dependabot configuration was. Update entries whose `package-ecosystem` has no known manifests are left untouched.",1,,GitHub Actions,,Recipes to perform [GitHub Actions](https://docs.github.com/en/actions) hygiene and migration tasks.,"[{""name"":""codeownersPath"",""type"":""String"",""displayName"":""`CODEOWNERS` path"",""description"":""Where to write the migrated reviewers when the repository does not have a `CODEOWNERS` file yet. Defaults to `.github/CODEOWNERS`. When a `CODEOWNERS` file already exists in any of the locations GitHub recognizes, that file is appended to instead and this option is ignored."",""example"":""CODEOWNERS""}]",
 maven,org.openrewrite.recipe:rewrite-github-actions,org.openrewrite.github.ReplaceOssrhSecretsWithSonatype,Replace OSSRH secrets with Sonatype secrets,Replace deprecated OSSRH_S01 secrets with new Sonatype secrets in GitHub Actions workflows. This is an example use of the `ReplaceSecrets` and `ReplaceSecretKeys` recipes combined used to update the Maven publishing secrets in OpenRewrite's GitHub organization.,5,,GitHub Actions,,Recipes to perform [GitHub Actions](https://docs.github.com/en/actions) hygiene and migration tasks.,,
 maven,org.openrewrite.recipe:rewrite-github-actions,org.openrewrite.github.ReplaceRunners,Replace runners for a job,Replaces the runners of a given job.,1,,GitHub Actions,,Recipes to perform [GitHub Actions](https://docs.github.com/en/actions) hygiene and migration tasks.,"[{""name"":""jobName"",""type"":""String"",""displayName"":""Job Name"",""description"":""The name of the job to update, use * to affect all the workflow jobs"",""example"":""build"",""required"":true},{""name"":""runners"",""type"":""List"",""displayName"":""Runners"",""description"":""The new list of runners to set"",""example"":""ubuntu-latest"",""required"":true}]",
 maven,org.openrewrite.recipe:rewrite-github-actions,org.openrewrite.github.ReplaceSecretKeys,Replace secret key names in GitHub Actions,Replace key names used for secrets in GitHub Actions workflow files.,1,,GitHub Actions,,Recipes to perform [GitHub Actions](https://docs.github.com/en/actions) hygiene and migration tasks.,"[{""name"":""oldKeyName"",""type"":""String"",""displayName"":""Old key name"",""description"":""The name of the key to be replaced"",""example"":""ossrh_username"",""required"":true},{""name"":""newKeyName"",""type"":""String"",""displayName"":""New key name"",""description"":""The new key name to use"",""example"":""sonatype_username"",""required"":true},{""name"":""fileMatcher"",""type"":""String"",""displayName"":""File matcher"",""description"":""Optional file path matcher"",""example"":"".github/workflows/*.{yml,yaml}""}]",
diff --git a/src/test/java/org/openrewrite/github/ReplaceDependabotReviewersWithCodeownersTest.java b/src/test/java/org/openrewrite/github/ReplaceDependabotReviewersWithCodeownersTest.java
new file mode 100644
index 0000000..47b5839
--- /dev/null
+++ b/src/test/java/org/openrewrite/github/ReplaceDependabotReviewersWithCodeownersTest.java
@@ -0,0 +1,740 @@
+/*
+ * Copyright 2025 the original author or authors.
+ * <p>
+ * Licensed under the Moderne Source Available License (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * <p>
+ * https://docs.moderne.io/licensing/moderne-source-available-license
+ * <p>
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.openrewrite.github;
+
+import org.junit.jupiter.api.Test;
+import org.openrewrite.DocumentExample;
+import org.openrewrite.test.RecipeSpec;
+import org.openrewrite.test.RewriteTest;
+
+import static org.openrewrite.test.SourceSpecs.other;
+import static org.openrewrite.test.SourceSpecs.text;
+import static org.openrewrite.yaml.Assertions.yaml;
+
+class ReplaceDependabotReviewersWithCodeownersTest implements RewriteTest {
+
+    @Override
+    public void defaults(RecipeSpec spec) {
+        spec.recipe(new ReplaceDependabotReviewersWithCodeowners(null));
+    }
+
+    @DocumentExample
+    @Test
+    void migrateReviewersToNewCodeownersFile() {
+        rewriteRun(
+          //language=yaml
+          yaml(
+            """
+              version: 2
+              updates:
+                - package-ecosystem: maven
+                  directory: /
+                  schedule:
+                    interval: weekly
+                  reviewers:
+                    - acme/backend
+                - package-ecosystem: npm
+                  directory: /frontend
+                  schedule:
+                    interval: weekly
+                  reviewers:
+                    - acme/frontend
+              """,
+            """
+              version: 2
+              updates:
+                - package-ecosystem: maven
+                  directory: /
+                  schedule:
+                    interval: weekly
+                - package-ecosystem: npm
+                  directory: /frontend
+                  schedule:
+                    interval: weekly
+              """,
+            spec -> spec.path(".github/dependabot.yml")
+          ),
+          text(
+            null,
+            """
+              # Reviewers migrated from the Dependabot configuration
+              /pom.xml @acme/backend
+              /frontend/package.json @acme/frontend
+              /frontend/package-lock.json @acme/frontend
+              /frontend/yarn.lock @acme/frontend
+              /frontend/pnpm-lock.yaml @acme/frontend
+              """,
+            spec -> spec.path(".github/CODEOWNERS")
+          )
+        );
+    }
+
+    @Test
+    void githubActionsMapsToWorkflowsDirectory() {
+        rewriteRun(
+          //language=yaml
+          yaml(
+            """
+              version: 2
+              updates:
+                - package-ecosystem: github-actions
+                  directory: /
+                  reviewers:
+                    - acme/devops
+              """,
+            """
+              version: 2
+              updates:
+                - package-ecosystem: github-actions
+                  directory: /
+              """,
+            spec -> spec.path(".github/dependabot.yml")
+          ),
+          text(
+            null,
+            """
+              # Reviewers migrated from the Dependabot configuration
+              /.github/workflows/ @acme/devops
+              """,
+            spec -> spec.path(".github/CODEOWNERS")
+          )
+        );
+    }
+
+    @Test
+    void appendToExistingCodeowners() {
+        rewriteRun(
+          //language=yaml
+          yaml(
+            """
+              version: 2
+              updates:
+                - package-ecosystem: maven
+                  directory: /
+                  reviewers:
+                    - acme/backend
+              """,
+            """
+              version: 2
+              updates:
+                - package-ecosystem: maven
+                  directory: /
+              """,
+            spec -> spec.path(".github/dependabot.yml")
+          ),
+          text(
+            """
+              * @acme/everyone
+              """,
+            """
+              * @acme/everyone
+
+              # Reviewers migrated from the Dependabot configuration
+              /pom.xml @acme/backend
+              """,
+            spec -> spec.path("CODEOWNERS")
+          )
+        );
+    }
+
+    @Test
+    void mergeIntoPatternAlreadyOwnedBySomeoneElse() {
+        rewriteRun(
+          //language=yaml
+          yaml(
+            """
+              version: 2
+              updates:
+                - package-ecosystem: maven
+                  directory: /
+                  reviewers:
+                    - acme/backend
+              """,
+            """
+              version: 2
+              updates:
+                - package-ecosystem: maven
+                  directory: /
+              """,
+            spec -> spec.path(".github/dependabot.yml")
+          ),
+          text(
+            """
+              /pom.xml @someone/else
+              """,
+            """
+              /pom.xml @someone/else @acme/backend
+              """,
+            spec -> spec.path("CODEOWNERS")
+          )
+        );
+    }
+
+    @Test
+    void doNotDuplicateOwnerAlreadyOnTheLine() {
+        rewriteRun(
+          //language=yaml
+          yaml(
+            """
+              version: 2
+              updates:
+                - package-ecosystem: maven
+                  directory: /
+                  reviewers:
+                    - acme/backend
+              """,
+            """
+              version: 2
+              updates:
+                - package-ecosystem: maven
+                  directory: /
+              """,
+            spec -> spec.path(".github/dependabot.yml")
+          ),
+          text(
+            """
+              /pom.xml @acme/backend @someone/else
+              """,
+            spec -> spec.path("CODEOWNERS")
+          )
+        );
+    }
+
+    @Test
+    void mergeSomeOwnersAndAppendOtherPatterns() {
+        rewriteRun(
+          //language=yaml
+          yaml(
+            """
+              version: 2
+              updates:
+                - package-ecosystem: gomod
+                  directory: /
+                  reviewers:
+                    - acme/backend
+              """,
+            """
+              version: 2
+              updates:
+                - package-ecosystem: gomod
+                  directory: /
+              """,
+            spec -> spec.path(".github/dependabot.yml")
+          ),
+          text(
+            """
+              # ownership
+              /go.mod @someone/else
+
+              /unrelated.txt @acme/docs
+              """,
+            """
+              # ownership
+              /go.mod @someone/else @acme/backend
+
+              /unrelated.txt @acme/docs
+
+              # Reviewers migrated from the Dependabot configuration
+              /go.sum @acme/backend
+              """,
+            spec -> spec.path("CODEOWNERS")
+          )
+        );
+    }
+
+    @Test
+    void individualReviewersArePrefixed() {
+        rewriteRun(
+          //language=yaml
+          yaml(
+            """
+              version: 2
+              updates:
+                - package-ecosystem: gomod
+                  directory: /
+                  reviewers:
+                    - octocat
+                    - "@hubot"
+              """,
+            """
+              version: 2
+              updates:
+                - package-ecosystem: gomod
+                  directory: /
+              """,
+            spec -> spec.path(".github/dependabot.yml")
+          ),
+          text(
+            null,
+            """
+              # Reviewers migrated from the Dependabot configuration
+              /go.mod @octocat @hubot
+              /go.sum @octocat @hubot
+              """,
+            spec -> spec.path(".github/CODEOWNERS")
+          )
+        );
+    }
+
+    @Test
+    void multipleDirectories() {
+        rewriteRun(
+          //language=yaml
+          yaml(
+            """
+              version: 2
+              updates:
+                - package-ecosystem: cargo
+                  directories:
+                    - /crates/one
+                    - /crates/two
+                  reviewers:
+                    - acme/rust
+              """,
+            """
+              version: 2
+              updates:
+                - package-ecosystem: cargo
+                  directories:
+                    - /crates/one
+                    - /crates/two
+              """,
+            spec -> spec.path(".github/dependabot.yml")
+          ),
+          text(
+            null,
+            """
+              # Reviewers migrated from the Dependabot configuration
+              /crates/one/Cargo.toml @acme/rust
+              /crates/one/Cargo.lock @acme/rust
+              /crates/two/Cargo.toml @acme/rust
+              /crates/two/Cargo.lock @acme/rust
+              """,
+            spec -> spec.path(".github/CODEOWNERS")
+          )
+        );
+    }
+
+    @Test
+    void unknownEcosystemIsLeftAlone() {
+        rewriteRun(
+          //language=yaml
+          yaml(
+            """
+              version: 2
+              updates:
+                - package-ecosystem: some-future-ecosystem
+                  directory: /
+                  reviewers:
+                    - acme/backend
+              """,
+            spec -> spec.path(".github/dependabot.yml")
+          )
+        );
+    }
+
+    @Test
+    void unknownEcosystemKeepsItsReviewersWhileOthersMigrate() {
+        rewriteRun(
+          //language=yaml
+          yaml(
+            """
+              version: 2
+              updates:
+                - package-ecosystem: some-future-ecosystem
+                  directory: /
+                  reviewers:
+                    - acme/future
+                - package-ecosystem: maven
+                  directory: /
+                  reviewers:
+                    - acme/backend
+              """,
+            """
+              version: 2
+              updates:
+                - package-ecosystem: some-future-ecosystem
+                  directory: /
+                  reviewers:
+                    - acme/future
+                - package-ecosystem: maven
+                  directory: /
+              """,
+            spec -> spec.path(".github/dependabot.yml")
+          ),
+          text(
+            null,
+            """
+              # Reviewers migrated from the Dependabot configuration
+              /pom.xml @acme/backend
+              """,
+            spec -> spec.path(".github/CODEOWNERS")
+          )
+        );
+    }
+
+    @Test
+    void noReviewersIsNoChange() {
+        rewriteRun(
+          //language=yaml
+          yaml(
+            """
+              version: 2
+              updates:
+                - package-ecosystem: maven
+                  directory: /
+                  schedule:
+                    interval: weekly
+              """,
+            spec -> spec.path(".github/dependabot.yml")
+          )
+        );
+    }
+
+    @Test
+    void codeownersPathIsConfigurable() {
+        rewriteRun(
+          spec -> spec.recipe(new ReplaceDependabotReviewersWithCodeowners("CODEOWNERS")),
+          //language=yaml
+          yaml(
+            """
+              version: 2
+              updates:
+                - package-ecosystem: maven
+                  directory: /
+                  reviewers:
+                    - acme/backend
+              """,
+            """
+              version: 2
+              updates:
+                - package-ecosystem: maven
+                  directory: /
+              """,
+            spec -> spec.path(".github/dependabot.yml")
+          ),
+          text(
+            null,
+            """
+              # Reviewers migrated from the Dependabot configuration
+              /pom.xml @acme/backend
+              """,
+            spec -> spec.path("CODEOWNERS")
+          )
+        );
+    }
+
+    @Test
+    void reviewersInFlowSequence() {
+        rewriteRun(
+          //language=yaml
+          yaml(
+            """
+              version: 2
+              updates:
+                - package-ecosystem: maven
+                  directory: /
+                  reviewers: [acme/backend, acme/platform]
+              """,
+            """
+              version: 2
+              updates:
+                - package-ecosystem: maven
+                  directory: /
+              """,
+            spec -> spec.path(".github/dependabot.yml")
+          ),
+          text(
+            null,
+            """
+              # Reviewers migrated from the Dependabot configuration
+              /pom.xml @acme/backend @acme/platform
+              """,
+            spec -> spec.path(".github/CODEOWNERS")
+          )
+        );
+    }
+
+    @Test
+    void multiEcosystemConfigurationFromIssue() {
+        rewriteRun(
+          //language=yaml
+          yaml(
+            """
+              version: 2
+              updates:
+
+              - package-ecosystem: gradle
+                directory: "/"
+                schedule:
+                  interval: weekly
+                reviewers:
+                  - "kafbat/backend"
+                open-pull-requests-limit: 10
+
+              - package-ecosystem: docker
+                directory: "/api"
+                schedule:
+                  interval: weekly
+                reviewers:
+                  - "kafbat/backend"
+                open-pull-requests-limit: 10
+
+              - package-ecosystem: npm
+                directory: "/frontend"
+                schedule:
+                  interval: weekly
+                reviewers:
+                  - "kafbat/frontend"
+                open-pull-requests-limit: 10
+
+              - package-ecosystem: "github-actions"
+                directory: "/"
+                schedule:
+                  interval: weekly
+                reviewers:
+                  - "kafbat/devops"
+                open-pull-requests-limit: 10
+              """,
+            """
+              version: 2
+              updates:
+
+              - package-ecosystem: gradle
+                directory: "/"
+                schedule:
+                  interval: weekly
+                open-pull-requests-limit: 10
+
+              - package-ecosystem: docker
+                directory: "/api"
+                schedule:
+                  interval: weekly
+                open-pull-requests-limit: 10
+
+              - package-ecosystem: npm
+                directory: "/frontend"
+                schedule:
+                  interval: weekly
+                open-pull-requests-limit: 10
+
+              - package-ecosystem: "github-actions"
+                directory: "/"
+                schedule:
+                  interval: weekly
+                open-pull-requests-limit: 10
+              """,
+            spec -> spec.path(".github/dependabot.yml")
+          ),
+          text(
+            null,
+            """
+              # Reviewers migrated from the Dependabot configuration
+              /build.gradle @kafbat/backend
+              /build.gradle.kts @kafbat/backend
+              /gradle/libs.versions.toml @kafbat/backend
+              /api/Dockerfile @kafbat/backend
+              /frontend/package.json @kafbat/frontend
+              /frontend/package-lock.json @kafbat/frontend
+              /frontend/yarn.lock @kafbat/frontend
+              /frontend/pnpm-lock.yaml @kafbat/frontend
+              /.github/workflows/ @kafbat/devops
+              """,
+            spec -> spec.path(".github/CODEOWNERS")
+          )
+        );
+    }
+
+    @Test
+    void appendsToDotGithubCodeownersWhenRootAlsoExists() {
+        rewriteRun(
+          //language=yaml
+          yaml(
+            """
+              version: 2
+              updates:
+                - package-ecosystem: maven
+                  directory: /
+                  reviewers:
+                    - acme/backend
+              """,
+            """
+              version: 2
+              updates:
+                - package-ecosystem: maven
+                  directory: /
+              """,
+            spec -> spec.path(".github/dependabot.yml")
+          ),
+          text(
+            """
+              * @acme/root
+              """,
+            spec -> spec.path("CODEOWNERS")
+          ),
+          text(
+            """
+              * @acme/everyone
+              """,
+            """
+              * @acme/everyone
+
+              # Reviewers migrated from the Dependabot configuration
+              /pom.xml @acme/backend
+              """,
+            spec -> spec.path(".github/CODEOWNERS")
+          )
+        );
+    }
+
+    @Test
+    void keepsReviewersWhenCodeownersCannotBeRead() {
+        rewriteRun(
+          //language=yaml
+          yaml(
+            """
+              version: 2
+              updates:
+                - package-ecosystem: maven
+                  directory: /
+                  reviewers:
+                    - acme/backend
+              """,
+            spec -> spec.path(".github/dependabot.yml")
+          ),
+          other(
+            "* @acme/everyone",
+            spec -> spec.path(".github/CODEOWNERS")
+          )
+        );
+    }
+
+    @Test
+    void secondRunIsANoOp() {
+        rewriteRun(
+          //language=yaml
+          yaml(
+            """
+              version: 2
+              updates:
+                - package-ecosystem: maven
+                  directory: /
+                  schedule:
+                    interval: weekly
+              """,
+            spec -> spec.path(".github/dependabot.yml")
+          ),
+          text(
+            """
+              # Reviewers migrated from the Dependabot configuration
+              /pom.xml @acme/backend
+              """,
+            spec -> spec.path(".github/CODEOWNERS")
+          )
+        );
+    }
+
+    @Test
+    void appendsToDotGithubCodeownersWhenLowerPrecedenceCodeownersCannotBeRead() {
+        rewriteRun(
+          //language=yaml
+          yaml(
+            """
+              version: 2
+              updates:
+                - package-ecosystem: maven
+                  directory: /
+                  reviewers:
+                    - acme/backend
+              """,
+            """
+              version: 2
+              updates:
+                - package-ecosystem: maven
+                  directory: /
+              """,
+            spec -> spec.path(".github/dependabot.yml")
+          ),
+          other(
+            "* @acme/everyone",
+            spec -> spec.path("docs/CODEOWNERS")
+          ),
+          text(
+            """
+              * @acme/everyone
+              """,
+            """
+              * @acme/everyone
+
+              # Reviewers migrated from the Dependabot configuration
+              /pom.xml @acme/backend
+              """,
+            spec -> spec.path(".github/CODEOWNERS")
+          )
+        );
+    }
+
+    @Test
+    void githubActionsInNonRootDirectoryMapsToCompositeAction() {
+        rewriteRun(
+          //language=yaml
+          yaml(
+            """
+              version: 2
+              updates:
+                - package-ecosystem: github-actions
+                  directory: /.github/actions/setup
+                  reviewers:
+                    - acme/devops
+              """,
+            """
+              version: 2
+              updates:
+                - package-ecosystem: github-actions
+                  directory: /.github/actions/setup
+              """,
+            spec -> spec.path(".github/dependabot.yml")
+          ),
+          text(
+            null,
+            """
+              # Reviewers migrated from the Dependabot configuration
+              /.github/actions/setup/action.yml @acme/devops
+              /.github/actions/setup/action.yaml @acme/devops
+              """,
+            spec -> spec.path(".github/CODEOWNERS")
+          )
+        );
+    }
+
+    @Test
+    void doesNotTouchOtherYamlFiles() {
+        rewriteRun(
+          //language=yaml
+          yaml(
+            """
+              version: 2
+              updates:
+                - package-ecosystem: maven
+                  directory: /
+                  reviewers:
+                    - acme/backend
+              """,
+            spec -> spec.path("some/other/dependabot-example.yml")
+          )
+        );
+    }
+}