GitHub Copilot Extensions

January 30, 2026

GitHub Copilot Extensions allow developers to build custom agents and integrations that leverage Copilot's AI capabilities. Create specialized assistants that understand your tools, services, and workflows.

What Are Copilot Extensions?

Copilot Extensions extend GitHub Copilot's capabilities beyond code completion. They're agents that can:

Answer questions about your systems
Execute actions on behalf of users
Integrate with external services
Provide domain-specific assistance

When a user mentions your extension (@your-extension), Copilot routes the request to your agent.

Architecture

┌─────────────┐    ┌─────────────┐    ┌─────────────┐
│   User      │───►│   GitHub    │───►│   Your      │
│   @agent    │    │   Copilot   │    │   Server    │
└─────────────┘    └─────────────┘    └─────────────┘

Your extension receives:

User messages
Conversation context
GitHub-authenticated user info

And responds with:

Text responses
Code suggestions
Action confirmations

Building an Extension

1. Create a GitHub App

Extensions are built on GitHub Apps:

# app.yml
name: my-copilot-extension
description: A helpful assistant for my service
public: true
default_events:
  - copilot_chat
default_permissions:
  copilot_chat: write

2. Handle Requests

Your server receives chat requests:

app.post('/copilot', async (req, res) => {
  const { messages, user } = req.body;
  
  // Process the user's message
  const lastMessage = messages[messages.length - 1];
  
  // Generate a response
  const response = await generateResponse(lastMessage.content);
  
  // Return to Copilot
  res.json({
    choices: [{
      message: {
        role: 'assistant',
        content: response,
      }
    }]
  });
});

3. Add Capabilities

Extensions can include:

Slash Commands: Predefined actions

/deploy - Deploy to production
/status - Check system status
/rollback - Rollback last deployment

References: Contextual data sources

@docs - Search documentation
@issues - Reference GitHub issues
@prs - Reference pull requests

Use Cases

DevOps Assistant

Help developers interact with infrastructure:

Check deployment status
View logs and metrics
Trigger CI/CD pipelines

Documentation Bot

Provide instant answers from your docs:

Search knowledge bases
Explain APIs and features
Generate code examples

Support Agent

First-line support within the IDE:

Troubleshoot common issues
Create support tickets
Escalate to humans

Integration with MCP

Copilot Extensions can connect to MCP servers for expanded capabilities:

import { createMcpClient } from '@modelcontextprotocol/sdk';

const mcpClient = createMcpClient({
  server: 'file://./my-mcp-server',
});

// Use MCP tools in your extension
const result = await mcpClient.callTool('search_docs', {
  query: userMessage,
});

Authentication

Extensions receive GitHub-verified user identity:

app.post('/copilot', async (req, res) => {
  const user = req.headers['x-github-user'];
  const token = req.headers['x-github-token'];
  
  // Verify and use GitHub identity
  const octokit = new Octokit({ auth: token });
  const repos = await octokit.repos.listForAuthenticatedUser();
});

Marketplace Distribution

Publish your extension to the GitHub Marketplace:

Build and test your extension
Submit for review
Once approved, users can install via Marketplace
Monetization options available

Limitations

Current limitations to be aware of:

Response latency requirements
Rate limits on requests
Context window constraints
Streaming support varies

When to Build an Extension

Good fit:

Have a service developers use daily
Want to meet developers in their IDE
Need authenticated access to GitHub data
Building internal developer tools

Consider alternatives when:

Need standalone agent (use OpenAI/Claude SDKs)
Building general-purpose agents (use LangChain)
Need complex multi-agent orchestration

Sources

GitHub Copilot Extensions Documentation — Official docs
GitHub Marketplace — Distribution
GitHub Apps — Foundation for extensions