Author, validate, and debug Copilot CLI canvas extensions rendered in the app side panel.
npx skills add https://github.com/github/gh-aw --skill create-canvas
Please help me install this Agent Skill. Skill: create-canvas Source: https://github.com/github/gh-aw/tree/main/.github/skills/create-canvas Command: npx skills add https://github.com/github/gh-aw --skill create-canvas
Building a canvas extension for the GitHub Copilot app involves a specific runtime contract — JSON-RPC over stdio, joinSession declaration, loopback HTTP servers, and a three-part ID model — and small mistakes like a stray console.log or a reserved action name silently break the extension. This Skill provides the exact authoring workflow, API reference, and debugging checklist to get a canvas working.
extensions_manage, edit extension.mjs, reload, and verify with list/inspect operations.createCanvas, open, actions[] handlers, onClose, input schema validation, and the loopback server pattern with Server-Sent Events.open_canvas and invoke_canvas_action.Ask the agent to scaffold a new project-scoped canvas extension named triage-board and walk through implementing and validating its open handler and actions.
High-intent search queries and answers about installing and using this skill.
Scaffold it with extensions_manage using operation scaffold, kind canvas, and a chosen location (project, user, or session). This generates an extension.mjs with joinSession, a createCanvas declaration, a loopback HTTP server, and an example action that you then edit and reload.
Run extensions_manage with operation list to check whether the extension is marked failed, then operation inspect to view its log file path and tail. After any edit, call extensions_reload before retrying, and confirm the file is named exactly extension.mjs in a discovered directory.
No. Extensions must be a single extension.mjs file using ES modules; TypeScript is not supported. stdout is reserved for JSON-RPC, so console.log corrupts the protocol — use session.log with a level and ephemeral flag instead.
canvasId identifies the canvas type declared by the extension, extensionId is the auto-derived source:name identifier used only to disambiguate duplicate canvasIds, and instanceId is a caller-chosen handle for one running panel. invoke_canvas_action requires an instanceId, not a canvasId.
Action names starting with the canvas. prefix are reserved by the runtime and rejected at declaration or invocation time. Rename the action to a custom verb that is unique within the canvas and does not use the reserved prefix.
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