feat: first class MCP support for native tool calling

[mcowger]

fixes #3229

Context

Implement dynamic MCP native tool generation support.

Available MCP servers are enumerated for their published tools, and dynamic tool definitions are generated
in the form of use_mcp_tool___servername___toolname.

Implementation

• Add helper functions to detect and parse dynamic MCP tool names
• Normalize dynamic tools to standard use_mcp_tool format
• Use triple underscores (___) as separator to allow underscores in tool names
• Extract toolInputProps and convert to JSON string for MCP server compatibility
• Renames properties called type to renamed_type internally before sending to model, because type is a reserved word for many parsers.
• Update tool name generation in mcp_server.ts
• Add test coverage for dynamic tool parsing

Screenshots

How to Test

Use an MCP server with JSON calling enabled. Ensure that MCP servers can be called, and that they produce expected results.

Get in Touch

mcowger

[changeset-bot]

🦋 Changeset detected

Latest commit: 312a863

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
kilo-code	Minor

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[chrarnoldus]

hm, I get this error trying the GitHub MCP:

[mcowger]

Got it. Lemme try that one and see where the bug is.

[mcowger]

hm, I get this error trying the GitHub MCP:

Can you provide a prompt or model combo that had this result? I can't replicate this:

[chrarnoldus]

I got the error with OpenRouter and GPT-5 (other models also give errors, but generic ones).

Prompt doesn't matter, "say hi" will do.

[mcowger]

I got the error with OpenRouter and GPT-5 (other models also give errors, but generic ones).

Prompt doesn't matter, "say hi" will do.

OK, I think I know whats up here. The MCP server defines a parameter called 'type'. The OpenAI spec doesn't mention any restrictions or reserved words for the contents of the parameters schema definition, but it definitely appears that at least OpenAI and SGlang barf on parameters called 'type'.

I'll need to think about how to handle this case.

[mcowger]

I don't particularly love this renaming solution @chrarnoldus - it feels hacky, but I don't really have a better idea. Open to suggestions.

I did confirm with qwen3-coder, haiku, GLM, and Sonnet 4.5, and with GH & Context7 MCPs

[chrarnoldus]

I'll try to think of other solutions as well, thanks for your work

[mcowger]

I will say...it does work pretty reliable.

[mcowger]

Closing in favor of #3288