Repomix Browser Extension Developer
yamadashy/repomix
Use this skill when developing or maintaining browser extension code in the `browser/` directory, including Chrome/Firefox/Edge compatibility, content…
Author a new PostHog browser extension, or port a posthog-js v1 extension, against the @posthog/browser-common Client/Extension contract.
Install Develop Extension
$ npx skills add PostHog/posthog-js --skill develop-extension -a claude-codeProject install by default; add -g for ~/.claude/skills/.
$ gh skill install PostHog/posthog-js develop-extension --agent claude-codeProject scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).
$ git clone --depth 1 https://github.com/PostHog/posthog-js.git skills-src && mkdir -p .claude/skills && cp -r skills-src/packages/browser-common/.agents/skills/develop-extension .claude/skills/develop-extension && rm -rf skills-srcUse ~/.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/
Install the "develop-extension" agent skill from https://github.com/PostHog/posthog-js/tree/main/packages/browser-common/.agents/skills/develop-extension into .claude/skills/develop-extension/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "develop-extension", then confirm the skill loads.Claude Code copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$skill-installer install https://github.com/PostHog/posthog-js/tree/main/packages/browser-common/.agents/skills/develop-extensionType this inside Codex. $skill-installer <name> installs a curated skill from openai/skills. The installer writes to $CODEX_HOME/skills (default ~/.codex/skills). Restart Codex if the skill does not show up.
$ npx skills add PostHog/posthog-js --skill develop-extension -a codexProject install goes to .agents/skills/; add -g for ~/.codex/skills/.
$ gh skill install PostHog/posthog-js develop-extension --agent codexProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/PostHog/posthog-js.git skills-src && mkdir -p .agents/skills && cp -r skills-src/packages/browser-common/.agents/skills/develop-extension .agents/skills/develop-extension && rm -rf skills-srcUse ~/.agents/skills/ instead of .agents/skills for a personal install.
Codex skills documentation · loads skills from .agents/skills/
Install the "develop-extension" agent skill from https://github.com/PostHog/posthog-js/tree/main/packages/browser-common/.agents/skills/develop-extension into .agents/skills/develop-extension/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "develop-extension", then confirm the skill loads.Codex copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ npx skills add PostHog/posthog-js --skill develop-extension -a cursorProject install goes to .agents/skills/; add -g for ~/.cursor/skills/.
$ gh skill install PostHog/posthog-js develop-extension --agent cursorProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/PostHog/posthog-js.git skills-src && mkdir -p .cursor/skills && cp -r skills-src/packages/browser-common/.agents/skills/develop-extension .cursor/skills/develop-extension && rm -rf skills-srcUse ~/.cursor/skills/ instead of .cursor/skills for a personal install.
Cursor skills documentation · loads skills from .cursor/skills/, .agents/skills/, .claude/skills/, .codex/skills/
Install the "develop-extension" agent skill from https://github.com/PostHog/posthog-js/tree/main/packages/browser-common/.agents/skills/develop-extension into .cursor/skills/develop-extension/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "develop-extension", then confirm the skill loads.Cursor copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ gemini skills install https://github.com/PostHog/posthog-js.git --path packages/browser-common/.agents/skills/develop-extension--scope user (default) or --scope workspace; --path is the subfolder of the repo that holds the skill; --consent skips the security confirmation prompt.
$ npx skills add PostHog/posthog-js --skill develop-extension -a gemini-cliProject install goes to .agents/skills/; add -g for ~/.gemini/skills/.
$ gh skill install PostHog/posthog-js develop-extension --agent gemini-cliProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/PostHog/posthog-js.git skills-src && mkdir -p .gemini/skills && cp -r skills-src/packages/browser-common/.agents/skills/develop-extension .gemini/skills/develop-extension && rm -rf skills-srcUse ~/.gemini/skills/ instead of .gemini/skills for a personal install, then run /skills reload.
Gemini CLI skills documentation · loads skills from .gemini/skills/, .agents/skills/
Install the "develop-extension" agent skill from https://github.com/PostHog/posthog-js/tree/main/packages/browser-common/.agents/skills/develop-extension into .gemini/skills/develop-extension/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "develop-extension", then confirm the skill loads.Gemini CLI copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ gh skill install PostHog/posthog-js develop-extensionInstalls for Copilot at project scope by default; add --scope user for a personal install. Preview a skill first with gh skill preview. Needs GitHub CLI 2.90.0 or later (public preview).
$ npx skills add PostHog/posthog-js --skill develop-extension -a github-copilotProject install goes to .agents/skills/; add -g for ~/.copilot/skills/.
$ git clone --depth 1 https://github.com/PostHog/posthog-js.git skills-src && mkdir -p .github/skills && cp -r skills-src/packages/browser-common/.agents/skills/develop-extension .github/skills/develop-extension && rm -rf skills-srcUse ~/.copilot/skills/ instead of .github/skills for a personal install. Commit .github/skills so cloud agent and code review can use it.
GitHub Copilot skills documentation · loads skills from .github/skills/, .claude/skills/, .agents/skills/
Install the "develop-extension" agent skill from https://github.com/PostHog/posthog-js/tree/main/packages/browser-common/.agents/skills/develop-extension into .github/skills/develop-extension/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "develop-extension", then confirm the skill loads.GitHub Copilot copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ npx skills add PostHog/posthog-js --skill develop-extension -a opencodeOpenCode documents no install command of its own. Project install goes to .agents/skills/; add -g for ~/.config/opencode/skills/.
$ gh skill install PostHog/posthog-js develop-extension --agent opencodeProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/PostHog/posthog-js.git skills-src && mkdir -p .opencode/skills && cp -r skills-src/packages/browser-common/.agents/skills/develop-extension .opencode/skills/develop-extension && rm -rf skills-srcUse ~/.config/opencode/skills/ instead of .opencode/skills for a personal install.
OpenCode skills documentation · loads skills from .opencode/skills/, .claude/skills/, .agents/skills/
Install the "develop-extension" agent skill from https://github.com/PostHog/posthog-js/tree/main/packages/browser-common/.agents/skills/develop-extension into .opencode/skills/develop-extension/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "develop-extension", then confirm the skill loads.OpenCode copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
Facts
- Skill name
develop-extension- GitHub stars
- 613
- Token cost
- ~2.3k tokens
- SKILL.md length
- 683 words
- Files
- 1
- Skills in repo
- 3
- Repo updated
- First seen
- Licence
- Custom licence
At a glance
Author a new PostHog browser extension, or port a posthog-js v1 extension, against the @posthog/browser-common Client/Extension contract.
- Porting an extension (autocapture
- SKILL.md covers The shape, Client capabilities, Hard rules and Event streams, plus 2 more sections
- Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md
- Campaign-params
What it does
Develop Extension is an agent skill from PostHog/posthog-js, published by the product's own GitHub organization. Author a new PostHog browser extension, or port a posthog-js v1 extension, against the @posthog/browser-common Client/Extension contract. Use when adding or porting an extension (autocapture, pageview, surveys, replay, exceptions, web-vitals, campaign-params, feature flags, …).
Its SKILL.md is about 2.3k tokens, which your agent loads only when the skill is triggered. It is a single SKILL.md file with no bundled scripts.
It sits in Development, covering Browser extensions and Web performance. It works with PostHog, Chrome Extensions, npm and JavaScript. The repository describes itself as: Send usage data from your web app or site to PostHog, with autocapture.
When your agent uses it
- Porting an extension (autocapture
- Campaign-params
Example prompts
- “/develop-extension”
What it can do on your machine
Read from SKILL.md and the folder at commit e75146a. 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
Develop Extension loads about 2.3k tokens when it runs. Until then it costs about 74 tokens; SKILL.md has 683 words of instructions outside code blocks.
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 683 words (~2,314 tokens).
“A browser extension is an opt-in feature that implements Extension and talks to its host SDK exclusively through the single Client adapter passed to setup and shared by extensions on that SDK instance. The contract is designed for extensions shared…”
- name
- develop-extension
Files
Just SKILL.md in packages/browser-common/.agents/skills/develop-extension of PostHog/posthog-js.
Open the folder on GitHubat commit e75146a
Compare with similar skills
Develop Extension 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.
| Skill | Stars | Used in | Tokens | Auto-check | Licence | Repo updated |
|---|---|---|---|---|---|---|
| Develop Extension this skillPostHog/posthog-js | 613 | — | ~2.3k | Automated safety check: Pass | Custom licence | |
| Repomix Browser Extension Developeryamadashy/repomix | 29k | 1 repos | ~288 | Automated safety check: Pass | MIT | |
| Htmlhintmanagedcode/dotnet-skills | 486 | — | ~1.2k | Automated safety check: Pass | MIT | |
| Webhintmanagedcode/dotnet-skills | 486 | — | ~1.3k | Automated safety check: Pass | MIT | |
| Install Anti-Slop Oxlint Rulesdmmulroy/anti-slop | 5.2k | — | ~2.2k | Automated safety check: Pass | MIT | |
| Release Roundethereumjs/ethereumjs-monorepo | 2.8k | — | ~2k | Automated safety check: Pass | None |
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Related
Categories
Questions about Develop Extension
What does Develop Extension do?
Author a new PostHog browser extension, or port a posthog-js v1 extension, against the @posthog/browser-common Client/Extension contract. Develop Extension is an agent skill from PostHog/posthog-js, published by the product's own GitHub organization. Author a new PostHog browser extension, or port a posthog-js v1 extension, against the @posthog/browser-common Client/Extension contract.
When should I use Develop Extension?
Develop Extension fits situations like: porting an extension (autocapture; campaign-params.
How do I install Develop Extension in Claude Code?
Run `npx skills add PostHog/posthog-js --skill develop-extension -a claude-code`. Or copy the skill folder (packages/browser-common/.agents/skills/develop-extension in PostHog/posthog-js) into .claude/skills/develop-extension in your project. Claude Code loads it when a task matches its description.
How do I install Develop Extension in Codex?
Run `npx skills add PostHog/posthog-js --skill develop-extension -a codex`. Or copy the skill folder (packages/browser-common/.agents/skills/develop-extension in PostHog/posthog-js) into .agents/skills/develop-extension in your project. Codex loads it when a task matches its description.
Can I use Develop Extension 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-js --skill develop-extension -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/develop-extension, .gemini/skills/develop-extension, .github/skills/develop-extension and .opencode/skills/develop-extension in your project.
What does Develop Extension need to run?
SKILL.md names no scripts, command-line tools or credentials: Develop Extension is instructions for the agent only.
Does Develop Extension 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 Develop Extension 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 Develop Extension use?
Develop Extension 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 Develop Extension use?
About 2.3k tokens (SKILL.md is roughly 9.3k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.
What are the alternatives to Develop Extension?
Skills that share tags, products or a category with Develop Extension: Repomix Browser Extension Developer (yamadashy/repomix, 29k stars), Htmlhint (managedcode/dotnet-skills, 486 stars), Webhint (managedcode/dotnet-skills, 486 stars) and Install Anti-Slop Oxlint Rules (dmmulroy/anti-slop, 5.2k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.
Who maintains Develop Extension?
PostHog (a GitHub organization, an official publisher) maintains it in PostHog/posthog-js, which has 613 GitHub stars. The repository holds 3 skills in this directory. The repository was last updated on October 7, 2026.
Source: PostHog/posthog-js on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.