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GitHub Copilot extends through MCP servers, custom instructions, and prompt files. Copilot has two surfaces with different MCP schemas, the in-editor agent (VS Code) and the autonomous coding agent (cloud), so they’re covered separately below.

MCP in VS Code

Create .vscode/mcp.json in the workspace. VS Code uses the servers key and requires a type:
Reload the window and the Smithers tools appear in Copilot Chat’s agent mode.

MCP in the Copilot coding agent

The autonomous coding agent is configured in repo Settings → Copilot → Coding agent → MCP configuration. It uses a different schema: mcpServers, a type of "local", and a tools array:
Secrets are Actions/Agents secrets prefixed COPILOT_MCP_ and referenced as $VAR in the env block. The semantic tool surface is the same on both surfaces; see the MCP Server reference.

Custom instructions

Copilot reads .github/copilot-instructions.md (repo-wide) and, for the coding agent, AGENTS.md. Add a section pointing at Smithers:
For a slash command, drop a prompt file at .github/prompts/smithers.prompt.md.

See also