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 (10): open_board, get_board, get_preview, add_text, add_link, add_image, draw_stroke, move, erase, wait_for_update. All ten have 1:1 REST mirrors at https://cnvs.app/api/boards/<id>/… for runtimes that can't speak MCP.
Resources (2): cnvs://board/{id}/state.json (full snapshot, subscribable) and cnvs://board/{id}/preview.svg (visual render, 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.

Installation

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.

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:

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  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.

cnvs.app