fix: normalize MCP tool schemas for Bedrock and OpenAI strict mode #10148
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Fixes an error where Bedrock/Claude rejects tool definitions that use
the deprecated type: ["T", "null"] array syntax for nullable types.
This syntax was valid in JSON Schema draft-04 through draft-07, but is
not valid in JSON Schema draft 2020-12 which Claude on Bedrock requires.
The fix adds a normalizeToolSchema() function that uses Zod to:
- Transform type: ["T", "null"] to anyOf: [{type: "T"}, {type: "null"}]
- Set additionalProperties: false by default (required by OpenAI strict mode)
- Recursively apply transformations to nested schemas
Closes: https://us.posthog.com/error_tracking/019b29fd-1546-7f61-b95d-a485cf010623
Contributor
Review complete. No issues found. The new commit correctly extends JSON Schema 2020-12 normalization to MCP tool schemas. The implementation adds empty Mention @roomote in a comment to request specific changes to this pull request or fix all unresolved issues. |
- Convert type arrays (e.g., ["string", "null"]) to anyOf format for JSON Schema 2020-12 compliance (Bedrock)
- Filter required array to only include keys that exist in properties
- Add empty properties: {} for type: "object" schemas without properties (OpenAI strict mode)
- Use normalizeToolSchema() in mcp_server.ts instead of ToolInputSchema.safeParse()
- Update tests to expect properties: {} for bare object schemas
cte
approved these changes
Dec 17, 2025
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Summary
Fixes MCP tool schema normalization for both Bedrock (JSON Schema 2020-12) and OpenAI (strict mode) compatibility.
Root Cause
type: ["string", "null"]is invalid in JSON Schema 2020-12type: "object"withoutpropertiesviolates strict mode (e.g.,launchOptions: { type: "object" })Changes
src/utils/json-schema.ts: Enhanced Zod transform to:type: ["T", "null"]→anyOfformat (JSON Schema 2020-12)requiredto only include keys that exist inpropertiesproperties: {}fortype: "object"schemas without properties (OpenAI strict mode)src/core/prompts/tools/native-tools/mcp_server.ts: UsenormalizeToolSchema()instead ofToolInputSchema.safeParse()src/utils/__tests__/json-schema.spec.ts: Updated tests to expectproperties: {}for bare object schemasTesting
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