Web Application Testing
anthropics/skills
Tests local web applications with Python Playwright scripts, checking frontend behavior, capturing screenshots and reading browser console logs.
A skill your agent uses when building features with Codex (OpenAI Codex CLI) in any codebase and the work should go through a disciplined build → review → test → fix loop.
Install Build Loop Codex
$ npx skills add BuildGreatProducts/builder-os --skill build-loop-codex -a claude-codeProject install by default; add -g for ~/.claude/skills/.
$ gh skill install BuildGreatProducts/builder-os build-loop-codex --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/BuildGreatProducts/builder-os.git skills-src && mkdir -p .claude/skills && cp -r skills-src/skills/build-loop-codex .claude/skills/build-loop-codex && 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 "build-loop-codex" agent skill from https://github.com/BuildGreatProducts/builder-os/tree/main/skills/build-loop-codex into .claude/skills/build-loop-codex/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "build-loop-codex", 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/BuildGreatProducts/builder-os/tree/main/skills/build-loop-codexType 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 BuildGreatProducts/builder-os --skill build-loop-codex -a codexProject install goes to .agents/skills/; add -g for ~/.codex/skills/.
$ gh skill install BuildGreatProducts/builder-os build-loop-codex --agent codexProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/BuildGreatProducts/builder-os.git skills-src && mkdir -p .agents/skills && cp -r skills-src/skills/build-loop-codex .agents/skills/build-loop-codex && rm -rf skills-srcUse ~/.agents/skills/ instead of .agents/skills for a personal install.
Codex skills documentation · loads skills from .agents/skills/
Install the "build-loop-codex" agent skill from https://github.com/BuildGreatProducts/builder-os/tree/main/skills/build-loop-codex into .agents/skills/build-loop-codex/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "build-loop-codex", 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 BuildGreatProducts/builder-os --skill build-loop-codex -a cursorProject install goes to .agents/skills/; add -g for ~/.cursor/skills/.
$ gh skill install BuildGreatProducts/builder-os build-loop-codex --agent cursorProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/BuildGreatProducts/builder-os.git skills-src && mkdir -p .cursor/skills && cp -r skills-src/skills/build-loop-codex .cursor/skills/build-loop-codex && 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 "build-loop-codex" agent skill from https://github.com/BuildGreatProducts/builder-os/tree/main/skills/build-loop-codex into .cursor/skills/build-loop-codex/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "build-loop-codex", 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/BuildGreatProducts/builder-os.git --path skills/build-loop-codex--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 BuildGreatProducts/builder-os --skill build-loop-codex -a gemini-cliProject install goes to .agents/skills/; add -g for ~/.gemini/skills/.
$ gh skill install BuildGreatProducts/builder-os build-loop-codex --agent gemini-cliProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/BuildGreatProducts/builder-os.git skills-src && mkdir -p .gemini/skills && cp -r skills-src/skills/build-loop-codex .gemini/skills/build-loop-codex && 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 "build-loop-codex" agent skill from https://github.com/BuildGreatProducts/builder-os/tree/main/skills/build-loop-codex into .gemini/skills/build-loop-codex/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "build-loop-codex", 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 BuildGreatProducts/builder-os build-loop-codexInstalls 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 BuildGreatProducts/builder-os --skill build-loop-codex -a github-copilotProject install goes to .agents/skills/; add -g for ~/.copilot/skills/.
$ git clone --depth 1 https://github.com/BuildGreatProducts/builder-os.git skills-src && mkdir -p .github/skills && cp -r skills-src/skills/build-loop-codex .github/skills/build-loop-codex && 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 "build-loop-codex" agent skill from https://github.com/BuildGreatProducts/builder-os/tree/main/skills/build-loop-codex into .github/skills/build-loop-codex/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "build-loop-codex", 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 BuildGreatProducts/builder-os --skill build-loop-codex -a opencodeOpenCode documents no install command of its own. Project install goes to .agents/skills/; add -g for ~/.config/opencode/skills/.
$ gh skill install BuildGreatProducts/builder-os build-loop-codex --agent opencodeProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/BuildGreatProducts/builder-os.git skills-src && mkdir -p .opencode/skills && cp -r skills-src/skills/build-loop-codex .opencode/skills/build-loop-codex && 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 "build-loop-codex" agent skill from https://github.com/BuildGreatProducts/builder-os/tree/main/skills/build-loop-codex into .opencode/skills/build-loop-codex/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "build-loop-codex", 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
build-loop-codex- GitHub stars
- 227
- Token cost
- ~888 tokens
- SKILL.md length
- 436 words
- Files
- 1
- Skills in repo
- 8
- Repo updated
- First seen
- Licence
- MIT
At a glance
A skill your agent uses when building features with Codex (OpenAI Codex CLI) in any codebase and the work should go through a disciplined build → review → test → fix loop.
- Works in 6 steps: Build. Implement exactly what the task… → Review. Run /review and select "Review… → Test end to end. Run the task's… → …
- Run the build loop
- SKILL.md covers Source of work, The loop and Rules
- Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md
What it does
Build Loop Codex is an agent skill from BuildGreatProducts/builder-os. Use when building features with Codex (OpenAI Codex CLI) in any codebase and the work should go through a disciplined build → review → test → fix loop. Triggers on "run the build loop", "build the next task", "continue the plan", "build this feature properly", or any request to implement work from a plan file or a direct feature prompt. Builds from the plan (or the prompt if no plan exists), runs Codex's /review on uncommitted changes and fixes every issue found, tests and verifies the feature end to end, fixes…
Its SKILL.md is about 890 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 Testing & QA, covering End-to-end testing. The repository describes itself as: BuilderOS is your operating system for building with AI. The licence is MIT.
When your agent uses it
- Run the build loop
- Build the next task
- Continue the plan
- Build this feature properly
Example prompts
- “run the build loop”
- “build the next task”
- “continue the plan”
- “/build-loop-codex”
Workflow steps
6 steps, taken from the first numbered list in SKILL.md.
- Build. Implement exactly what the task specifies. Simplest implementation that satisfies it, surgical changes, no speculative scope. Match…
- Review. Run /review and select "Review uncommitted changes". If the change touches auth, payments, user input, or data access, run a…
- Test end to end. Run the task's verification step (or the success criteria). Run the full test suite — everything that passed before must…
- Fix. Anything testing finds goes back through the loop: fix → /review → re-test. Never mark a failing task complete; never start the next…
- Continue. Mark the task - [x], update any progress/status line in the plan, and loop to the next task until the requested scope is complete.
- Report. When done, tell the user: what was built and plan progress, review findings fixed and anything deferred, how it was verified…
What it can do on your machine
Read from SKILL.md and the folder at commit fb74cac. 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.
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
Build Loop Codex loads about 888 tokens when it runs. Until then it costs about 161 tokens; SKILL.md has 436 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
The full file from BuildGreatProducts/builder-os at commit fb74cac, republished under its MIT licence (© BuildGreatProducts). 436 words, ~888 tokens.
Download SKILL.mdSave it as
.claude/skills/build-loop-codex/SKILL.md (or your agent's skills folder).- name
- build-loop-codex
- description
- Use when building features with **Codex** (OpenAI Codex CLI) in any codebase and the work should go through a disciplined build → review → test → fix loop. Triggers on "run the build loop", "build the next task", "continue the plan", "build this feature properly", or any request to implement work from a plan file or a direct feature prompt. Builds from the plan (or the prompt if no plan exists), runs Codex's `/review` on uncommitted changes and fixes every issue found, tests and verifies the feature end to end, fixes anything testing surfaces, and reports back once complete. Repeats until all plan tasks are checked off.
- license
- MIT
- metadata.author
- BuilderOS
- metadata.version
- 1.0
Codex Build Loop
Quality-gated feature work: nothing ships on "it compiles" — every increment is built, reviewed, tested end to end, and fixed before the user hears "done."
Source of work
- A plan file exists (roadmap, refactor plan, or task list with
- [ ]checkboxes — search the repo): work the first unchecked task. Tasks are ordered intentionally — never skip ahead. If the plan references spec docs, read only the sections relevant to the current task. - No plan (or the request is outside it): build from the user's prompt. Restate it as a verifiable goal with 2–4 success criteria and confirm scope in one message before building.
The loop
Run per task (or per prompted feature). Do not advance until every step passes.
Build. Implement exactly what the task specifies. Simplest implementation that satisfies it, surgical changes, no speculative scope. Match existing project conventions.
Review. Run
/reviewand select "Review uncommitted changes". If the change touches auth, payments, user input, or data access, run a second pass via "Custom review instructions" (e.g. "Focus on security vulnerabilities and unvalidated input"). Fix all findings in scope — bugs, security issues, edge cases, performance, style in files you touched. If the project has a design system spec (design tokens file, DESIGN.md, theme config), check UI changes against it — no hardcoded colors, type, or spacing that bypass tokens. Note pre-existing issues in untouched code for the report instead of fixing silently. Re-run/reviewuntil clean. If a finding contradicts the task or spec, the spec wins — flag the disagreement.Test end to end. Run the task's verification step (or the success criteria). Run the full test suite — everything that passed before must still pass. Add tests for new logic. Then exercise the feature as a user would: run the app, walk the real flow including empty, loading, and error states.
Fix. Anything testing finds goes back through the loop: fix →
/review→ re-test. Never mark a failing task complete; never start the next task with the app broken.Continue. Mark the task
- [x], update any progress/status line in the plan, and loop to the next task until the requested scope is complete.Report. When done, tell the user: what was built and plan progress, review findings fixed and anything deferred, how it was verified (tests + flow walked), and what needs their attention next. Be honest about anything flaky or partially verified.
Show full SKILL.md (39 more words)Show less
Rules
- Skipped review or untested work = unfinished work.
- Don't relitigate plan decisions; if a task seems wrong, ask one specific question rather than guessing.
- Discovered work no task covers? Surface it and propose a task — never silently expand scope.
© BuildGreatProducts, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file
Files
Just SKILL.md in skills/build-loop-codex of BuildGreatProducts/builder-os.
Open the folder on GitHubat commit fb74cac
Compare with similar skills
Build Loop Codex 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 |
|---|---|---|---|---|---|---|
| Build Loop Codex this skillBuildGreatProducts/builder-os | 227 | — | ~888 | Automated safety check: Pass | MIT | |
| Web Application Testinganthropics/skills | 180k | 51 repos | ~966 | Automated safety check: Pass | Apache-2.0 | |
| TDD WorkflowhellangleZ/burn-in-cceverywhere-ralph | 112 | 11 repos | ~2.4k | Automated safety check: Pass | None | |
| Uloop Replay Inputkurotu/VRCQuestTools | 373 | 3 repos | ~615 | Automated safety check: Pass | MIT | |
| Ui4 Convert Testspayloadcms/payload | 45k | — | ~3.5k | Automated safety check: Pass | MIT | |
| E2Estackia/rtp2httpd | 2.2k | — | ~517 | Automated safety check: Pass | GPL-2.0 |
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Related
Categories
Questions about Build Loop Codex
What does Build Loop Codex do?
A skill your agent uses when building features with Codex (OpenAI Codex CLI) in any codebase and the work should go through a disciplined build → review → test → fix loop. Build Loop Codex is an agent skill from BuildGreatProducts/builder-os. Use when building features with Codex (OpenAI Codex CLI) in any codebase and the work should go through a disciplined build → review → test → fix loop.
When should I use Build Loop Codex?
Build Loop Codex fits situations like: run the build loop; build the next task; continue the plan; build this feature properly.
How do I install Build Loop Codex in Claude Code?
Run `npx skills add BuildGreatProducts/builder-os --skill build-loop-codex -a claude-code`. Or copy the skill folder (skills/build-loop-codex in BuildGreatProducts/builder-os) into .claude/skills/build-loop-codex in your project. Claude Code loads it when a task matches its description.
How do I install Build Loop Codex in Codex?
Run `npx skills add BuildGreatProducts/builder-os --skill build-loop-codex -a codex`. Or copy the skill folder (skills/build-loop-codex in BuildGreatProducts/builder-os) into .agents/skills/build-loop-codex in your project. Codex loads it when a task matches its description.
Can I use Build Loop Codex 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 BuildGreatProducts/builder-os --skill build-loop-codex -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/build-loop-codex, .gemini/skills/build-loop-codex, .github/skills/build-loop-codex and .opencode/skills/build-loop-codex in your project.
What does Build Loop Codex need to run?
SKILL.md names no scripts, command-line tools or credentials: Build Loop Codex is instructions for the agent only.
Does Build Loop Codex 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 Build Loop Codex 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 Build Loop Codex use?
Build Loop Codex is published under the MIT licence (declared in SKILL.md). It allows redistribution, so the full SKILL.md is shown on this page.
How many tokens does Build Loop Codex use?
About 888 tokens (SKILL.md is roughly 3.6k 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 Build Loop Codex?
Skills that share tags, products or a category with Build Loop Codex: Web Application Testing (anthropics/skills, 180k stars), TDD Workflow (hellangleZ/burn-in-cceverywhere-ralph, 112 stars), Uloop Replay Input (kurotu/VRCQuestTools, 373 stars) and Ui4 Convert Tests (payloadcms/payload, 45k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.
Who maintains Build Loop Codex?
BuildGreatProducts (a GitHub user) maintains it in BuildGreatProducts/builder-os, which has 227 GitHub stars. The repository holds 8 skills in this directory. The repository was last updated on July 7, 2026.
Source: BuildGreatProducts/builder-os on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.