cnvs-whiteboard-skills

Agent Skills + MCP server discovery for cnvs.app — the free, no-signup real-time collaborative whiteboard. Any AI agent can read, write, draw, diagram, and subscribe to live human edits on a shared canvas, either through the hosted MCP server or the REST fallback.

Works with Claude Code, Claude Desktop, Cursor, OpenCode / OpenAI Codex, Aider (with MCP plugin), any other MCP-speaking client, and Hermes-family agents.

MCP Server

Endpoint: https://cnvs.app/mcp (Streamable HTTP, protocol 2025-06-18, no auth — the board ID is the access key).

Registered in the official MCP Registry as app.cnvs/whiteboard.

Capabilities

• Tools (25): board creation and inspection; visual previews; text, link, image, and stroke editing; movement and deletion; live-update waits; and complete kanban column, lane, task, query, and export workflows. The exact production list is published in /.well-known/mcp.json. State-changing operations also have REST mirrors under https://cnvs.app/api/boards/<id>/… for runtimes that cannot speak MCP.

• Resources (3): cnvs://board/{id}/state.json (full snapshot), cnvs://board/{id}/preview.svg (visual render), and cnvs://board/{id}/tasks.json (kanban state). All three are subscribable.

• Subscriptions: resources/subscribe supported with notifications/resources/updated pushed over SSE, debounced ~3 s after activity settles.

• Live machine-readable manifests: /quotas.json, /openapi.json, /llms.txt, /.well-known/mcp.json, /.well-known/mcp/server.json.

Related MCP server: Excalidraw MCP Server

Installation

Codex / ChatGPT and Cursor packages

This repository is the public source package for both marketplace integrations:

• .codex-plugin/plugin.json and .mcp.json describe the Codex / ChatGPT plugin.

• .cursor-plugin/plugin.json and mcp.json describe the Cursor plugin.

• SUBMISSION.md and CURSOR-MARKETPLACE.md contain the prepared listing copy, disclosures, reviewer flows, and submission checklists.

Both packages connect only to the hosted production endpoint; there is no local server process or secret to configure.

Claude Desktop / Cursor / any MCP client

One-line config — add this to your client's mcpServers object:

{
  "mcpServers": {
    "cnvs": {
      "type": "http",
      "url": "https://cnvs.app/mcp"
    }
  }
}

Claude Code CLI

claude mcp add --transport http cnvs https://cnvs.app/mcp

REST-only (no MCP client)

# Create a board
curl -X POST https://cnvs.app/api/boards

# Add text
curl -X POST https://cnvs.app/api/boards/<id>/texts \
  -H 'Content-Type: application/json' \
  -d '{"x":100,"y":200,"content":"# Hello","author":"ai:myagent"}'

# Long-poll for live changes
curl "https://cnvs.app/api/boards/<id>/wait?timeout_ms=25000"

Full REST reference: /llms.txt, /openapi.json.

Access model

There is no account or OAuth flow. A board URL or board ID is a bearer-style access credential: anyone who knows an unlocked board URL can open it. Boards can optionally require an 8-character lowercase alphanumeric access key for writes or for both reads and writes; legacy 6-character keys remain accepted. Pass a key only through the MCP tool's access_key argument or the X-Board-Key HTTP header.

Do not paste private board URLs or access keys into public issues, logs, or repositories.

Useful prompts

• Create a fresh whiteboard for our brainstorming session and return its URL.

• Open this cnvs.app board, inspect its preview, and summarize the layout.

• Turn this list into a shared kanban board with priorities and owners.

Skills included

Two related Agent Skills live in this repo, published under the agentskills.io open standard so they work in any compatible runtime. Install them into ~/.claude/skills/ to teach the agent how to use the MCP server well (preview-before-JSON, REST-over-MCP for writes, author-tag conventions, subscription-then-react loop).

cnvs-whiteboard/ — PRIMARY

Teaches an AI agent how to collaborate on a cnvs.app board in real time:

• Read the shared canvas state

• Draw / diagram / flowchart / annotate — add, update, move, and delete text, links, sticky notes, strokes, images, and Mermaid diagrams (flowcharts, sequence / class / ER diagrams, mind maps, gantt charts, concept maps)

• Render the SVG preview when the board contains drawings

• Subscribe to live human edits via MCP, react via REST

Activates on any cnvs.app board reference (URL https://cnvs.app/#<id>, cnvs://board/<id>/..., or a bare board ID) or phrases like "collaborate on / draw / diagram / annotate / watch a shared whiteboard or canvas."

mcp-listen/ — HELPER (v0.3.0)

Push-to-model pump for Streamable-HTTP MCP servers with capabilities.resources.subscribe: true. Opens a session, subscribes to the resource URIs the caller hands over, and emits one JSON line per notifications/resources/updated event on stdout — designed to be wrapped by Claude Code's Monitor tool so every server push becomes an in-chat notification (no polling, no log tailing).

Helper-only activation since v0.3. Triggers only when the caller — a user or another skill — has supplied both an MCP server URL and at least one resource URI. Does NOT auto-activate from generic phrasing like "watch this file" or "stay in the loop". cnvs-whiteboard is the canonical caller and delegates its push channel here.

Output split since v0.3. Only the actionable resource_updated event reaches stdout by default. Connection / subscription / heartbeat / transient-error events go to stderr so a wrapping Monitor doesn't fire on the listener's own bookkeeping. Pass --verbose (or -v) to merge everything onto stdout for debugging or single-channel logging (legacy v0.2 behavior).

Registry status. Intentionally not listed in centralised skill registries yet. Current registry pipelines (e.g. majiayu000/claude-skill-registry-core as of 2026-05-03) archive only SKILL.md + generated metadata; they do not mirror bundled scripts/** or package.json, so an entry for mcp-listen would publish a broken skill. It will be (re-)submitted once core registries support directory-style skill archival with bundled-file mirroring and security scanning — see PR majiayu000/claude-skill-registry-core#40 for the directory-archive primitive that just landed and the open question on bundled-script scanning. Until then, install it via curl from cnvs.app (below) or git clone this repo.

Install the skills

# cnvs-whiteboard (SKILL.md only — no deps)
mkdir -p ~/.claude/skills/cnvs-whiteboard && cd ~/.claude/skills/cnvs-whiteboard
curl -O https://cnvs.app/cnvs-whiteboard/SKILL.md

# mcp-listen (SKILL.md + scripts/ + npm install)
mkdir -p ~/.claude/skills/mcp-listen && cd ~/.claude/skills/mcp-listen
curl -O https://cnvs.app/mcp-listen/SKILL.md \
     -O https://cnvs.app/mcp-listen/package.json \
     --create-dirs -o scripts/listen.mjs https://cnvs.app/mcp-listen/scripts/listen.mjs
npm install

Alternatively git clone this repo and cp -r .claude/skills/* ~/.claude/skills/ — the .claude/skills/ directory contains symlinks into cnvs-whiteboard/ and mcp-listen/ for Claude Code's expected layout.

Spec compliance

Both skills follow the agentskills.io spec:

• name matches the containing directory name

• description under 1024 characters, imperative phrasing, explicit trigger keywords

• scripts/ subdirectory for bundled code (mcp-listen)

• license: MIT, compatibility field declared, cross-references in each skill's "Related skills" section to prevent activation overlap

Why two skills

Earlier versions had a single page (/skill-cnvs.md on cnvs.app — now a legacy redirect). Splitting into two coherent units follows the spec's "design coherent units" best practice:

• cnvs-whiteboard owns the cnvs.app-specific workflow (read / write / render / gotchas).

• mcp-listen owns the generic push-to-model pattern (usable against any MCP server).

Cross-references keep them pairing cleanly: cnvs-whiteboard mentions mcp-listen as its delegated push channel; mcp-listen mentions cnvs-whiteboard as the companion for cnvs-specific work. No activation overlap in practice.

Canonical sources

Skills are also served live at:

• https://cnvs.app/cnvs-whiteboard/SKILL.md

• https://cnvs.app/mcp-listen/SKILL.md

• https://cnvs.app/mcp-listen/scripts/listen.mjs

• https://cnvs.app/mcp-listen/package.json

The cnvs.app URLs are the canonical install targets for curl-based installers; this GitHub repo is the reference for aggregators that crawl public sources (skills.sh, etc.) and for users who prefer git clone.

Discovery surfaces

Live

• Official MCP Registry: app.cnvs/whiteboard — browse

• cnvs.app /.well-known/mcp.json — links both skills

• cnvs.app /.well-known/mcp/server.json — MCP Registry entry with publisher-provided _meta.skills[]

• cnvs.app /llms.txt — LLM-friendly full reference

• majiayu000/claude-skill-registry-core — cnvs-whiteboard listed (PR #31 merged 2026-05-04). mcp-listen intentionally held back; see Registry status on the mcp-listen/ section above.

• Lobehub (used by Hermes agent) — both skills imported; MCP server submitted

Planned / under consideration

Notes for future expansion of distribution. Not active yet — kept here so the next maintenance window doesn't have to re-discover the landscape.

• majiayu000/claude-skill-registry-core — re-submit mcp-listen as a separate PR now that PR #40 (directory archives + bundled-script security scanning) is merged. scripts/listen.mjs is even hardcoded into their test assertions, so the pipeline already exercises our exact case.

• daymade/claude-code-skills (vendored model) — fork, copy cnvs-whiteboard/ and mcp-listen/ directly into their tree (their layout already expects scripts//references//assets/), update marketplace.json, single PR for both skills. No bundled-files concern because the files are copied in.

• VoltAgent/awesome-agent-skills (curated awesome-list, 20k ⭐) — markdown link, ≤10-word description. Their CONTRIBUTING explicitly excludes brand-new skills ("give your skill time to mature and gain users before submitting"); revisit once there's documented external usage.

• sickn33/antigravity-awesome-skills (36k ⭐) — manual path: fork, add skills/<name>/SKILL.md, run npm run validate. Their <!-- registry-sync: ... --> header in README suggests automated pull from upstream registries, so a successful entry on majiayu000/claude-skill-registry-core may propagate here without a separate PR — confirm before submitting twice.

• agentskills/agentskills (17.8k ⭐, the spec org behind agentskills.io) — investigate whether they accept reference implementations; mcp-listen as a worked example of MCP resources/subscribe consumption could fit there.

• vercel-labs/agent-skills / vercel-labs/skills — almost certainly curated, but read CONTRIBUTING before ruling out.

Skipped intentionally: anthropics/skills (curated, no community PRs); personal collections under ~100 ⭐; language-specific lists unless a relevant audience emerges.

License

MIT. See LICENSE.