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Official agent skill

Building Canvases

by PostHog in PostHog/posthog

Create or edit a PostHog freeform canvas — a sandboxed browser application (data board, document, form, small tool, graphics experiment) stored in PostHog and rendered by the desktop/web app.

OfficialCustom licenceAuto-check passed

Install Building Canvases

skills CLI
$ npx skills add PostHog/posthog --skill building-canvases -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI
$ gh skill install PostHog/posthog building-canvases --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy
$ git clone --depth 1 https://github.com/PostHog/posthog.git skills-src && mkdir -p .claude/skills && cp -r skills-src/products/canvas/skills/building-canvases .claude/skills/building-canvases && rm -rf skills-src

Use ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.

Claude Code skills documentation · loads skills from .claude/skills/

Facts

Skill name
building-canvases
GitHub stars
40k
Token cost
~3.9k tokens
SKILL.md length
2,017 words
Files
2 (incl. references)
Skills in repo
252
Repo updated
First seen
Licence
Custom licence

At a glance

Create or edit a PostHog freeform canvas — a sandboxed browser application (data board, document, form, small tool, graphics experiment) stored in PostHog and rendered by the desktop/web app.

  • Works in 4 steps: Put each panel in its own component. The… → Spread editable(name, props, params)… → Use the component with literal props,… → …
  • A task asks to build
  • SKILL.md covers Resolve the target canvas, Load the companion skills for…, Blocks and Params, plus 5 more sections
  • Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md

What it does

Building Canvases is an agent skill from PostHog/posthog, published by the product's own GitHub organization. Create or edit a PostHog freeform canvas — a sandboxed browser application (data board, document, form, small tool, graphics experiment) stored in PostHog and rendered by the desktop/web app. Use when a task asks to build, generate, update, or fix a standalone canvas app, or when a freeform canvas id is given as the publish target. For grid/home canvases, widget placements, or reusable components, use composing-grid-canvases instead. Covers resolving or creating the target canvas, choosing an implementation…

Its SKILL.md is about 3.9k tokens, which your agent loads only when the skill is triggered. The skill folder holds 2 other files, including reference files (for example `references/blocks.md`).

It works with PostHog and React. The repository describes itself as: :hedgehog: PostHog is the leading platform for building self-driving products. Our developer tools – AI observability, analytics, session replay, flags, experiments, error…

When your agent uses it

  • A task asks to build
  • Fix a standalone canvas app
  • A freeform canvas id is given as the publish target

Example prompts

  • “/building-canvases”

Workflow steps

4 steps, taken from the first numbered list in SKILL.md.

  1. Put each panel in its own component. The component takes these values as props, with defaults.
  2. Spread editable(name, props, params) from @posthog/canvas-sdk on the root element of the component. name is the component name. params…
  3. Use the component with literal props, for example . The editor writes changes into these props, so do not compute them inline.
  4. Give each use a unique blockId prop, for example , so a person can point the agent at one card. Use only letters, digits, _, -, ., and…

What it can do on your machine

Read from SKILL.md and the folder at commit 812e5c6. It shows what the files ask for, not the result of running them.

  • Tool permissions

    Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

    From allowed-tools in the SKILL.md frontmatter.

  • Runs code

    No scripts in the folder and no shell commands in SKILL.md (its code samples are typescript).

    From the folder's file list and the shell code blocks in SKILL.md.

  • Network

    No URLs in SKILL.md.

    From URLs in SKILL.md, links to its own repository left out.

  • Credentials

    Names no API keys, tokens, secrets or passwords.

    From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Building Canvases loads about 3.9k tokens when it runs, and up to ~5.5k if it reads all its reference files. Until then it costs about 173 tokens; SKILL.md has 2,017 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~173
When it runs · the whole SKILL.md, loaded when a task matches
~3.9k
With references · SKILL.md plus every file in references/, read only if the agent opens them
~5.5k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Auto-check passed

The automated check found no risky patterns in SKILL.md.

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

Its licence (Custom licence) doesn't allow us to republish the file, so here is its outline and opening line. It has 2,017 words (~3,900 tokens).

“A canvas is a client-side browser application that runs in a sandboxed iframe inside PostHog. Its source lives in PostHog — not in a repository — and you read and write it through the canvas-* tools. Never write a canvas…”

— opening of SKILL.md by PostHog, Custom licence
name
building-canvases

Read the full SKILL.md on GitHub

Files

SKILL.md and 1 other file (references) in products/canvas/skills/building-canvases of PostHog/posthog.

  • SKILL.md
  • references/blocks.md

Open the folder on GitHubat commit 812e5c6

Used in 1 other repository

We found 1 copy of this SKILL.md (exact, near-identical or edited) in other folders. This page covers the copy in PostHog/posthog, which our catalogue first saw on October 7, 2026.

Compare with similar skills

Building Canvases next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.

Building Canvases compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Building Canvases this skillPostHog/posthog40k—~3.9kAutomated safety check: PassCustom licence
C15tc15t/c15t1.9k1 repos~1.6kAutomated safety check: PassApache-2.0
Integration Astro Staticwill-be-done/will-be-done152—~636Automated safety check: PassAGPL-3.0
Canvas TemplatesPostHog/code179—~2.2kAutomated safety check: PassMIT
Quill CodePostHog/code179—~1.1kAutomated safety check: PassMIT
Flags SDKvercel/vercel-plugin301—~6.9kAutomated safety check: NotesCustom licence

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Works with

Questions about Building Canvases

What does Building Canvases do?

Create or edit a PostHog freeform canvas — a sandboxed browser application (data board, document, form, small tool, graphics experiment) stored in PostHog and rendered by the desktop/web app. Building Canvases is an agent skill from PostHog/posthog, published by the product's own GitHub organization. Create or edit a PostHog freeform canvas — a sandboxed browser application (data board, document, form, small tool, graphics experiment) stored in PostHog and rendered by the desktop/web app.

When should I use Building Canvases?

Building Canvases fits situations like: A task asks to build; fix a standalone canvas app; A freeform canvas id is given as the publish target.

How do I install Building Canvases in Claude Code?

Run `npx skills add PostHog/posthog --skill building-canvases -a claude-code`. Or copy the skill folder (products/canvas/skills/building-canvases in PostHog/posthog) into .claude/skills/building-canvases in your project. Claude Code loads it when a task matches its description.

How do I install Building Canvases in Codex?

Run `npx skills add PostHog/posthog --skill building-canvases -a codex`. Or copy the skill folder (products/canvas/skills/building-canvases in PostHog/posthog) into .agents/skills/building-canvases in your project. Codex loads it when a task matches its description.

Can I use Building Canvases in Cursor, Gemini CLI or GitHub Copilot?

Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add PostHog/posthog --skill building-canvases -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/building-canvases, .gemini/skills/building-canvases, .github/skills/building-canvases and .opencode/skills/building-canvases in your project.

What does Building Canvases need to run?

SKILL.md names no scripts, command-line tools or credentials: Building Canvases is instructions for the agent only.

Does Building Canvases access the network?

SKILL.md contains no URLs. Any network use would come from the scripts or tools the agent runs. This is read from the text; nothing was executed.

Is Building Canvases safe to install?

Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.

What licence does Building Canvases use?

Building Canvases has a licence file (the repository's licence) that doesn't match a standard licence. Read it on GitHub before reusing the skill.

How many tokens does Building Canvases use?

About 3.9k tokens (SKILL.md is roughly 16k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full. Its references folder adds about 1.6k tokens, read only when the agent opens those files.

What are the alternatives to Building Canvases?

Skills that share tags, products or a category with Building Canvases: C15t (c15t/c15t, 1.9k stars), Integration Astro Static (will-be-done/will-be-done, 152 stars), Canvas Templates (PostHog/code, 179 stars) and Quill Code (PostHog/code, 179 stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Building Canvases?

PostHog (a GitHub organization, an official publisher) maintains it in PostHog/posthog, which has 40,200 GitHub stars. The repository holds 252 skills in this directory. The repository was last updated on October 9, 2026.

Source: PostHog/posthog on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.