fix(mcp): emit properties:{} in list_agents inputSchema (#1889)#1892
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fix(mcp): emit properties:{} in list_agents inputSchema (#1889)#1892pboers1988 wants to merge 2 commits into
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Pull request overview
Fixes MCP list_agents tool schema compatibility with OpenAI strict-mode clients by ensuring the advertised inputSchema for a no-arg tool includes an explicit "properties": {} field, and adds a regression test using an in-memory MCP transport.
Changes:
- Set an explicit JSON Schema on the
list_agentsMCP tool so it serializes with"properties": {}and keepsadditionalProperties: false. - Add a unit test that starts an in-memory MCP server/client and asserts the
list_agentsschema shape. - Expose the underlying MCP server from
MCPHandler(currently used by the new test).
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.
| File | Description |
|---|---|
| go/core/internal/mcp/mcp_handler.go | Explicitly defines list_agents input schema and adds a server accessor used by tests. |
| go/core/internal/mcp/mcp_handler_test.go | Adds regression test verifying list_agents inputSchema includes properties: {} and additionalProperties: false. |
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…t-dev#1889) Signed-off-by: Peter Boers <peter.boers@surf.nl>
Empty input struct reflection produced inputSchema without a properties
key, which OpenAI strict mode rejects. Set InputSchema explicitly so the
serialized schema is {type:object, properties:{}, additionalProperties:false}.
Fixes kagent-dev#1889
Signed-off-by: Peter Boers <peter.boers@surf.nl>
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Summary
list_agentsMCP tool was advertisinginputSchema: {type: "object", additionalProperties: false}— nopropertieskey. OpenAI strict-mode clients (e.g. LibreChat via Agentgateway) reject this with400 Invalid schema for function 'list_agents_mcp_<server>': object schema missing properties.Tool.InputSchemaexplicitly so the serialized schema is{type: "object", properties: {}, additionalProperties: false}, matching whatinvoke_agent(and OpenAI strict mode) expect.Fixes #1889.
Test plan
go test ./core/internal/mcp/...passes locallygo testpassesgo test ./core/test/e2e/...(existing e2e) still passestools/listagainst a local controller shows"properties": {}onlist_agents