fix: use mcp_ prefix for tools (port from pi-coding-agent)

[lenstr]

Summary

Fixes the OAuth tool calling that broke after PR #10's oc_ prefix was blocked by Anthropic.

This is a port of the solution from pi-coding-agent which encountered and fixed the same issue.

Changes

1. Changed prefix from oc_ to mcp_ - This is what pi-coding-agent uses for Anthropic OAuth.

2. Added prefix to tool_use blocks in messages - PR fix: claude oauth by renaming tools on in/out #10 only prefixed tool definitions, but not tool calls in conversation history. This caused issues when the model tried to continue conversations with previous tool calls.

Testing locally

1. Clone and checkout this branch:

git clone https://github.com/lenstr/opencode-anthropic-auth.git
cd opencode-anthropic-auth
git checkout fix/mcp-tool-prefix

2. Add to your opencode.json:

{
  "plugin": [
    "file://<path-to>/opencode-anthropic-auth/index.mjs"
  ]
}

3. Run with default plugins disabled:

OPENCODE_DISABLE_DEFAULT_PLUGINS=true opencode

Reference

• pi-coding-agent anthropic provider - see mcp_ prefix handling for OAuth tokens

[DavidNorena]

Question guys, im just getting used to use opencode

could i temporarily clone this and test it locally like this ?

opencode.json
{
  "plugin": [
    "/home/myuser/.local/share/opencode-anthropic-auth"
  ],
  "$schema": "https://opencode.ai/config.json"
}

so far is not working for me

[lenstr]

Use file:// URL pointing to the index.mjs file:

{
  "plugin": [
    "file://<path-to>/opencode-anthropic-auth/index.mjs"
  ]
}

[devxoul]

You such a genius. I can confirm this works.

[DavidNorena]

should i select use api keys or claude pro sub when i connect, so far is not working for me

{
  "plugin": [
    "file:///home/myuser/.local/share/opencode-anthropic-auth/index.mjs"
  ],
  "$schema": "https://opencode.ai/config.json"
}

[lenstr]

Ah yes, you should run it like this:

OPENCODE_DISABLE_DEFAULT_PLUGINS=true opencode

[DavidNorena]

confirm !! it works ! thanks so much !

[Profpatsch]

We’re so back!

[ai-vampire]

hi @lenstr , thanks for this solution but im getting this error: "ish: Job 1, 'OPENCODE_DISABLE_DEFAULT_PLUGIN...' terminated by signal SIGABRT (Abort)"
when i starting opencode with this command: "OPENCODE_DISABLE_DEFAULT_PLUGINS=true opencode"

[lenstr]

This should be fixed in the latest opencode version. Try updating.