Copilot Limiter
Copilot Limiter is a VS Code extension that pins the subagents invoked by VS Code's Copilot Agent to one selected Copilot model.
Features
- Select an available Copilot model with
Copilot Limiter: Select Subagent Model
- Save the selected model ID and qualified name as the policy for
runSubagent
- Rewrite
runSubagent's tool_input.model to the selected model with the PreToolUse hook in .github/hooks/copilot-limiter.json
- Audit launched subagents with the
SubagentStart hook and record them in .github/copilot-limiter/runSubagent-audit.jsonl
Requirements
- Visual Studio Code 1.125.0 or later
- Signed in to GitHub Copilot Chat
- Copilot models available through the Language Model API
Usage
- Install the extension in an Extension Development Host or from a VSIX.
- Run
Copilot Limiter: Select Subagent Model from the Command Palette.
- Select the Copilot model to allow for subagents. The model policy and hook are generated.
- Invoke a subagent from the regular Copilot Agent. The hook rewrites the
runSubagent model to the selected value.
The generated hook rewrites the model input before runSubagent runs. It targets the current VS Code tool name when it is runSubagent, agent/runSubagent, or an equivalent name, and records the actual tool name, requested model, and enforced model in the audit log.
When you configure a different model, the selection command updates the model policy and hook. If you edit the configuration file directly, run Copilot Limiter: Apply Model Policy.
Commands
Copilot Limiter: Select Subagent Model: Select a Copilot model and generate or update the model policy and hookCopilot Limiter: Apply Model Policy: Regenerate the model policy and hook from the current settingsCopilot Limiter: Show Policy Status: Show the current model ID and display name
Settings
copilotLimiter.subagentModelId: The exact ID of the selected Copilot model. This is normally set by the selection command.copilotLimiter.subagentModelName: The qualified model name passed to the hook. This is normally set by the selection command.
Hook Limitations
Agent hooks are a Preview feature. Because SubagentStart cannot change the model itself, model enforcement depends on updatedInput from PreToolUse. If VS Code changes the runSubagent input schema or tool name in the future, check the audit log and Agent Debug Logs and update the hook as needed.
If the hook is not loaded or the runSubagent input is not an object, the hook rejects the request instead of guessing a model and executing it. This enforcement path is unavailable in environments where Agent hooks are disabled by organizational policy.
To disable the generated hook, delete .github/hooks/copilot-limiter.json and, if necessary, .github/copilot-limiter.
API Limitations
Without a hook, the public VS Code extension API cannot monitor calls to the standard Copilot Agent's internal runSubagent from the side. This extension is intended for workspaces where the hook is enabled.
If you need to govern all sessions across an organization, use the organization-wide AI policies for VS Code and GitHub Copilot as well.
Development
npm install
npm run compile
npm run lint
npm test
Press F5 to launch an Extension Development Host, then select a model from the Command Palette to verify the behavior.
Release Notes
0.0.1
- Initial implementation of Copilot Limiter
