opencode-anthropic-user-agent-plugin

Portable OpenCode plugin that injects a configurable Anthropic User-Agent for:

• Claude Pro/Max OAuth login
• OAuth token refresh
• Anthropic prompt/message requests
• Anthropic API key creation

The plugin works by patching fetch inside the OpenCode process for requests to Anthropic hosts, so it can affect both auth traffic and normal model I/O without patching OpenCode's cached plugin files by hand.

Install

Install the package:

npm install opencode-anthropic-user-agent-plugin

Then add it to your OpenCode config:

{
  "plugin": ["opencode-anthropic-user-agent-plugin"]
}

Restart OpenCode.

If Anthropic auth was already failing before you installed the plugin, re-run:

opencode auth login -p anthropic -m "Claude Pro/Max"

Default behavior

By default, the plugin uses this user-agent automatically:

anthropic

No environment variable is required.

Optional override

If you want a different value, override it with an environment variable:

export OPENCODE_ANTHROPIC_USER_AGENT='Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/18.3 Safari/605.1.15'

Then restart OpenCode.

Notes

• The plugin targets api.anthropic.com, console.anthropic.com, and claude.ai.
• It intentionally avoids patching unrelated hosts.
• Because it patches fetch, it should be compatible with OpenCode's built-in Anthropic auth plugin instead of replacing it.

Development / publishing

This repo includes a GitHub Actions workflow that publishes to npm on tags like:

git tag v0.1.1
git push origin v0.1.1

To enable publishing, add this repository secret:

• NPM_TOKEN: an npm automation token with publish access for this package