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Gemini API rejects JSON Schema containing $ref references #12295
Description
Problem
Gemini API rejects schemas containing $ref alongside other fields, causing errors like:
$ref 'QuestionOption' was set alongside unsupported fields.
If a schema node has $ref set, then only description and default can be set alongside it
This happens when MCP tools use JSON Schema with $ref references to $defs/definitions.
Expected Behavior
OpenCode should expand $ref references before sending schemas to Gemini API.
Related Issues
- Gemini API rejects MCP tool schemas with $defs references google-gemini/gemini-cli#13326 - Gemini API rejects MCP tool schemas with
$defsreferences - Error with Gemini models when MCP enabled #5832 - Error with Gemini models when MCP enabled
- Gemini Bad Request with Github Copilot #8417 - Gemini Bad Request with Github Copilot
Related PRs
- fix: apply schema transformation to MCP tools for Gemini compatibility #11968 - Applies schema transformation to MCP tools (complementary fix)
Reacted by Ikhsan Maulana
Activity
github-actions commentedon Feb 5, 2026
This issue might be a duplicate of existing issues. Please check:
Additionally, #11968 is a related PR that applies schema transformation to MCP tools - you may want to verify if extending that fix to handle
$refexpansion would solve this issue.Feel free to ignore if none of these address your specific case.
fix(google): sanitize unsupported JSON Schema keywords for Gemini API
github-actions commentedon Apr 7, 2026
To stay organized issues are automatically closed after 90 days of no activity. If the issue is still relevant please open a new one.