Cursor: extensions, plugins and skills (no MCP required)

Which mechanism matches a "mod"?

Claude Desktop mods change the app's own UI. Cursor has no first-party equivalent today; revisit when it ships one. Until then, match by intent:

Canvas is not a mod. It is an artifact the agent builds next to the chat. Its docs describe no authoring API, no component registration and no way to alter Cursor itself. Treat community claims about .canvas.tsx files and a cursor/canvas import as unverified.

Unofficial CSS/JS injection hacks for Cursor's workbench exist. They are unsupported, break on updates and are out of scope. Do not recommend them as a standard path.

Extensions in short

• Cursor installs third-party extensions from Open VSX through Cursor's proxy (marketplace.cursorapi.com), which runs malware and supply-chain analysis. It does not use the Microsoft Marketplace.
• To reach Cursor users, publish the same .vsix to Open VSX (ovsx publish). Publishing only to the Microsoft Marketplace leaves Cursor users to sideload.
• Users can always install a .vsix by hand.
• Stick to the open VS Code API. Microsoft-proprietary APIs and backends may not work.
• Teams may restrict installs by allowlist, signature verification and install cooldown. Publisher verification is available by request.

Full workflow, testing and publishing: references/vscode-extensions.md.

Skills (packaging for agent behavior)

• Loaded from .agents/skills/, .cursor/skills/, ~/.agents/skills/, ~/.cursor/skills/, and for compatibility .claude/skills/, .codex/skills/ and their ~/ forms.
• name and description are required; name must equal the folder name.
• Built-in helpers: /canvas, /create-skill, /create-rule, /create-hook, /create-subagent.

Plugins

Two formats. Details: references/plugins.md.

A path in the manifest replaces the default folder; it does not add to it.

Workflow

1. Pick the row in the table above. Do not add MCP for a panel.
2. Extension: scaffold, build, test in the Extension Development Host or sideload the .vsix in Cursor, then publish to Open VSX.
3. Plugin: author under .cursor-plugin/, test from ~/.cursor/plugins/local/<name> after a window reload.
4. Team sharing: Dashboard, Plugins and MCPs, Import from Repo.
5. Public plugin listing: https://cursor.com/marketplace/publish (manual review, open source).

Safety

• Extensions run with full user privileges. Request minimal activation events and capabilities, keep webview content security policy strict, and never ship secrets in a .vsix, manifest, rule, skill or canvas.
• Never put an Open VSX token in the repo or logs.
• Review hooks as code: they run commands on the user's machine.
• Do not publish to Open VSX, submit to a marketplace, tag or push without the user's explicit go-ahead this turn.
• Do not claim a canvas authoring API exists.

Checklist

• Right mechanism chosen from the table.
• Extension publisher.name is unique on Open VSX; namespace claimed.
• Extension tested in Cursor itself, not only VS Code.
• Plugin name lowercase kebab-case; manifest paths start with ./ and stay inside the plugin.
• ${CURSOR_PLUGIN_ROOT} used in mcp.json, not ${PLUGIN_ROOT}.

Anti-patterns

• Calling Canvas a mod or an extension API.
• Adding MCP just to get a panel.
• Publishing only to the Microsoft Marketplace and expecting Cursor discovery.
• Declaring a custom skills path and forgetting it replaces skills/.

Pointers