fix(mcp): respond to ping requests with an empty result

[joaopedroassad]

Background

I noticed that MCPClient.onRequestMessage replies with a JSON-RPC method not found error (-32601) to every incoming request that isn't elicitation/create. That includes ping.

Per the MCP specification on ping and the JSON-RPC contract, a ping receiver has to respond with an empty result. MCP servers commonly ping their connected clients on an idle timer to confirm the connection is still alive. When the client comes back with an error response instead, the server reads that as a broken peer and disconnects on the next keepalive cycle. If you're using experimental_createMCPClient against a server that does idle pings, your session eventually drops.

Summary

Three files touched:

• packages/mcp/src/tool/mcp-client.ts adds an early return branch in onRequestMessage for ping, sending back {jsonrpc: '2.0', id: request.id, result: {}}. The shape mirrors the existing elicitation/create send. No changes to public types or anything users see.
• packages/mcp/src/tool/mcp-client.test.ts adds a ping support describe block built on the same pattern as the existing elicitation support test. It pushes a ping JSON-RPC request through the mock transport and asserts the client replies with result: {}.
• .changeset/mcp-ping-response.md is the patch changeset.

Manual Verification

Before applying the fix on main, I added the new ping support test and watched it fail. The client came back with a -32601 error response instead of an empty result, which is exactly what #6282 describes. With the fix in place, the same test passes, and so do all 61 pre-existing tests in mcp-client.test.ts.

End to end, this corresponds to running an MCP server that pings on idle (any stdio server using the spec-recommended keepalive cadence), connecting with experimental_createMCPClient, and leaving the session quiet past the server's ping interval. Before the fix, the server disconnected when an error response landed. After the fix, the empty result keeps the session alive.

Checklist

• All commits are signed (PRs with unsigned commits cannot be merged)
• Tests have been added / updated (for bug fixes / features)
• Documentation has been added / updated (for bug fixes / features)
• A patch changeset for relevant packages has been added (for bug fixes / features, run pnpm changeset in the project root)
• I have reviewed this pull request (self-review)

Related Issues

Closes #6282

[github-actions]

✅ Backport PR created: #15715

[github-actions]

🚀 Published in:

Package	Version
@ai-sdk/google	4.0.0-canary.75 github npm
@ai-sdk/google-vertex	5.0.0-canary.98 github npm
@ai-sdk/mcp	2.0.0-canary.56 github npm
@ai-sdk/react	4.0.0-canary.162 github npm
@ai-sdk/xai	4.0.0-canary.69 github npm