Summary
Every tool in @perplexity-ai/mcp-server fails immediately in MCP clients that validate embedded schemas as JSON Schema 2020-12. The call is rejected at the client's schema-validation layer and never reaches the Perplexity API, so no request is billed — the tools are simply unusable.
Error
Tool 'perplexity_ask' has an invalid outputSchema: JSON Schema declares an
unsupported dialect ("$schema": "http://json-schema.org/draft-07/schema#").
The default validator supports JSON Schema 2020-12 only; pass a
pre-configured Ajv instance to Ajv...
Identical failure on perplexity_ask, perplexity_search, perplexity_reason, and perplexity_research. Not intermittent — it fails on every call, immediately, with no network activity.
Environment
@perplexity-ai/mcp-server — current latest from npm, installed globally via npm install -g- Client: Claude desktop app (Cowork), macOS
- Confirmed the installed version matches
npm view @perplexity-ai/mcp-server version, so this reproduces on the current release
Reproduce
npm install -g @perplexity-ai/mcp-server- Register it in an MCP client that validates
outputSchema against 2020-12
- Call any tool
Cause
The tools declare outputSchema with "$schema": "http://json-schema.org/draft-07/schema#". This is the well-known zod-to-json-schema default in the MCP TypeScript SDK — see [typescript-sdk#745](modelcontextprotocol/typescript-sdk#745). Note the string does not appear in dist/index.js; it originates in the dependency at schema-generation time, so it cannot be patched by editing the built entry point.
Suggested fix, in order of preference
- Emit 2020-12. Zod v4's
toJSONSchema({ target: "draft-2020-12" }), or pass the 2020-12 target explicitly to zod-to-json-schema.
- Drop
outputSchema entirely. It is optional in the MCP spec. Removing it restores every client immediately at the cost of advertising structured output, and would make a good stopgap release while option 1 lands.
Spec note
[SEP-1613](https://modelcontextprotocol.io/seps/1613-establish-json-schema-2020-12-as-default-dialect-f) (Final) makes 2020-12 the default dialect but permits servers to declare another via $schema, and requires clients to validate against the declared dialect. So this is arguably a shared problem — strict clients are rejecting something the spec allows. That said, servers MUST "generate schemas conforming to 2020-12 by default," and moving this server to 2020-12 fixes it for every affected client without waiting on any of them.
Summary
Every tool in
@perplexity-ai/mcp-serverfails immediately in MCP clients that validate embedded schemas as JSON Schema 2020-12. The call is rejected at the client's schema-validation layer and never reaches the Perplexity API, so no request is billed — the tools are simply unusable.Error
Identical failure on
perplexity_ask,perplexity_search,perplexity_reason, andperplexity_research. Not intermittent — it fails on every call, immediately, with no network activity.Environment
@perplexity-ai/mcp-server— current latest from npm, installed globally vianpm install -gnpm view @perplexity-ai/mcp-server version, so this reproduces on the current releaseReproduce
npm install -g @perplexity-ai/mcp-serveroutputSchemaagainst 2020-12Cause
The tools declare
outputSchemawith"$schema": "http://json-schema.org/draft-07/schema#". This is the well-knownzod-to-json-schemadefault in the MCP TypeScript SDK — see [typescript-sdk#745](modelcontextprotocol/typescript-sdk#745). Note the string does not appear indist/index.js; it originates in the dependency at schema-generation time, so it cannot be patched by editing the built entry point.Suggested fix, in order of preference
toJSONSchema({ target: "draft-2020-12" }), or pass the 2020-12 target explicitly tozod-to-json-schema.outputSchemaentirely. It is optional in the MCP spec. Removing it restores every client immediately at the cost of advertising structured output, and would make a good stopgap release while option 1 lands.Spec note
[SEP-1613](https://modelcontextprotocol.io/seps/1613-establish-json-schema-2020-12-as-default-dialect-f) (Final) makes 2020-12 the default dialect but permits servers to declare another via
$schema, and requires clients to validate against the declared dialect. So this is arguably a shared problem — strict clients are rejecting something the spec allows. That said, servers MUST "generate schemas conforming to 2020-12 by default," and moving this server to 2020-12 fixes it for every affected client without waiting on any of them.