Model call failed: {"message":"tools: Tool names must be unique.","code":"invalid_request_body"}

[doggy8088]

Describe the bug

Start from today. The error keeps appearing.

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 Version 0.0.353 · Commit f8fd3e3

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 ● Logged in with gh as user: doggy8088

 ● Configured MCP servers: Context7, chrome-devtools

 ● Connected to GitHub MCP Server

 > hi

 ✗ Model call failed: {"message":"tools: Tool names must be unique.","code":"invalid_request_body"} (Request ID:
   EBA2:1C5BEE:2291FC:27985E:6908E7A8)

 ✗ Model call failed: {"message":"tools: Tool names must be unique.","code":"invalid_request_body"} (Request ID:
   EBA2:1C5BEE:22AD20:27B7E0:6908E7A9)

Affected version

0.0.353 Commit: f8fd3e3

Steps to reproduce the behavior

1. Run copilot --allow-all-tools --allow-all-path
2. Type hi

Expected behavior

I expected to run without error.

Additional context

I tried to remove ~/.copilot/mcp-config.json file. The error still happen.

I suspect the problem is caused by the GitHub MCP Server. But, even I disabled GitHub MCP Server. The error still exist.

Logs:

2025-11-03T17:46:39.155Z [ERROR] {
  "stack": "CAPIError: 400 tools: Tool names must be unique.\n    at t.fromAPIError (file:///home/will/.nvm/versions/node/v22.16.0/lib/node_modules/@github/copilot/index.js:1905:898)\n    at J1e.getCompletionWithTools (file:///home/will/.nvm/versions/node/v22.16.0/lib/node_modules/@github/copilot/index.js:1905:5284)\n    at process.processTicksAndRejections (node:internal/process/task_queues:105:5)\n    at async Ude.getCompletionWithTools (file:///home/will/.nvm/versions/node/v22.16.0/lib/node_modules/@github/copilot/index.js:1906:1431)\n    at async Bil (file:///home/will/.nvm/versions/node/v22.16.0/lib/node_modules/@github/copilot/index.js:2456:573)\n    at async t.getCompletionWithTools (file:///home/will/.nvm/versions/node/v22.16.0/lib/node_modules/@github/copilot/index.js:2460:58389)\n    at async z7n (file:///home/will/.nvm/versions/node/v22.16.0/lib/node_modules/@github/copilot/index.js:2486:19713)\n    at async epl (file:///home/will/.nvm/versions/node/v22.16.0/lib/node_modules/@github/copilot/index.js:2486:16987)",
  "message": "400 tools: Tool names must be unique.",
  "status": 400,
  "headers": {},
  "requestID": "00000-b3d6972e-aa67-4600-9393-c0ded6b0bc62",
  "error": {
    "message": "tools: Tool names must be unique.",
    "code": "invalid_request_body"
  },
  "code": "invalid_request_body",
  "request_id": "00000-b3d6972e-aa67-4600-9393-c0ded6b0bc62",
  "ghRequestId": "EBB2:CA1DD:28404A:2E68C1:6908EA7D",
  "name": "CAPIError"
}

After removing the .github/agents/ folder, everything is working correctly now. I believe the error message could be improved.

[doggy8088]

I have a .github/agents/通靈模式.agent.md file in my working tree. The content of the file below:

---
name: 通靈模式
description: '協助開發者瞭解整個專案的現況與專案架構。'
tools: ['changes', 'codebase', 'fetch', 'search', 'searchResults', 'usages']
---
You are a helpful assistant providing insights on the current status and architecture of the project.

Answer only in zh-tw

I tried to remove this file or rename this file are all able to run Copilot CLI correctly. I don't know what's the issue of this file. Why this custom agent cause entire Copilot CLI failed?

By thy way, I also have another agent files. The others are all okay!

❯ tree -a .github/agents/
.github/agents/
├── CSharpExpert.agent.md
├── SQL 大師模式 (Read-Only).agent.md
├── SQL 大師模式.agent.md
├── 架構模式.agent.md
└── 通靈模式.agent.md

I don't know why this is happening.

[ellismg]

I don't know why this is happening.

I suspect the issue here is that we recently added some code that normalizes the ids (which is based on the name property) of custom agents so that characters outside of the range [A-Za-z0-9_-] are replaced with just an -. This obviously does not work great in the case of the names you have here, since both the 架構模式.agent.md and 通靈模式.agent.md custom agents are likely to both end up being named something like ---- after this normalization process. That appears to be what is happening here.

We will go make changes to the normalization process, but in the mean time to work around this issue, you could consider adding a few ASCII letters to the end of these two tool names which differ between the two. That should make it so we don't generate identitcal tool names after noramlization in this case.

I'm guessing that the problem is 架構模式.agent.md's name is likely 架構模式 and that it's conflicting with 通靈模式.agent.md's name after normalization.

[doggy8088]

I'm guessing that the problem is 架構模式.agent.md's name is likely 架構模式 and that it's conflicting with 通靈模式.agent.md's name after normalization.

I think what you said makes a lot of sense, it is very likely caused by that, thanks for the clarification!

[ellismg]

As an FYI @doggy8088, I made some changes to our normalization strategy that should address this issue (I validated that I was able to reproduce your issue with two custom agents with different names in unicode but the same number of characters). They will be in 0.0.355, which hasn't been released yet (hopefully soon!), but you can see the changes in the pre-release version via npm install -g @github/copilot@prerelease.