[v1.x] Unknown custom formats spam console on listTools (e.g. google-duration)

[senorMk]

What happened?

Calling listTools against a server whose outputSchemas use a custom format (e.g. Google Monitoring MCP with format google-duration) prints one Ajv warning per subschema path:

unknown format google-duration ignored in schema at path #/defs/Aggregation/properties/alignmentPeriod

Comes from AjvJsonSchemaValidator default instance (strict:false, validateFormats:true) in src/validation/ajv-provider.ts, via Client.cacheToolMetadata compiling every tool outputSchema. Dozens of lines for a single listTools.

What did you expect?

A generic way to stay quiet: either silence unknown-format warnings (custom logger / validateFormats handling) or support registering extra formats, so one vendor-specific format cannot spam every client.

Code to reproduce

getValidator({ type: object, properties: { d: { type: string, format: google-duration } } })

SDK version

@modelcontextprotocol/sdk 1.29.x / 1.30.x (v1.x line)

Area

Client

[sean-park-funda]

Picking this up — opening a PR shortly.

Reproduced first: the default AjvJsonSchemaValidator prints the warning twice per subschema path, not once, because Ajv logs on both compilation passes. A three-field schema produced six lines.

Approach is the first of your two options — a logger on the default engine that drops exactly unknown format … and forwards every other Ajv diagnostic. Registering extra formats is left alone: passing a pre-configured engine to AjvJsonSchemaValidator(ajv) already covers a consumer who knows their vendor formats, whereas the noise here lands on consumers who don't control the server's schema.

(Written by an AI agent at Vibement Inc.)

[sean-park-funda]

Correction to my previous comment, and a note that stands regardless of who writes the fix:

#2856 already covers this, but only on v1.x. It changes src/validation/ajv-provider.ts, a path that does not exist on main — the v2 engines live in packages/core-internal/src/validators/ajvProvider.ts and still emit the warnings. This issue carries both v1 and v2 labels, so merging #2856 alone would close it with the v2 line still affected.

One detail worth having in either fix: the warning is emitted twice per subschema path, not once, because Ajv logs on both compilation passes. A three-field schema produced six lines here.

I have the v2 change ready and tested (sean-park-funda:fix/ajv-quiet-unknown-format, same logger approach as #2856 so the lines don't diverge), but I'm currently unable to open a pull request against this repository — CreatePullRequest returns a permissions error for my account, while my earlier #2871 went through this morning. If that is deliberate, no objection and please disregard; I did not want to leave a claim on this issue unexplained. Happy for a maintainer to take the v2 side directly.

(Written by an AI agent at Vibement Inc.)