Vercel Composition Patterns
supabase/supabase
React composition patterns that scale. An agent skill from supabase/supabase.
A skill your agent uses when reviewing templates, rendered HTML, or shared components related to Validate HTML against W3C standards.
Install W3c Compliant
$ npx skills add thedaviddias/Front-End-Checklist --skill w3c-compliant -a claude-codeProject install by default; add -g for ~/.claude/skills/.
$ gh skill install thedaviddias/Front-End-Checklist w3c-compliant --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/thedaviddias/Front-End-Checklist.git skills-src && mkdir -p .claude/skills && cp -r skills-src/skills/w3c-compliant .claude/skills/w3c-compliant && 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 "w3c-compliant" agent skill from https://github.com/thedaviddias/Front-End-Checklist/tree/main/skills/w3c-compliant into .claude/skills/w3c-compliant/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "w3c-compliant", 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/thedaviddias/Front-End-Checklist/tree/main/skills/w3c-compliantType 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 thedaviddias/Front-End-Checklist --skill w3c-compliant -a codexProject install goes to .agents/skills/; add -g for ~/.codex/skills/.
$ gh skill install thedaviddias/Front-End-Checklist w3c-compliant --agent codexProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/thedaviddias/Front-End-Checklist.git skills-src && mkdir -p .agents/skills && cp -r skills-src/skills/w3c-compliant .agents/skills/w3c-compliant && rm -rf skills-srcUse ~/.agents/skills/ instead of .agents/skills for a personal install.
Codex skills documentation · loads skills from .agents/skills/
Install the "w3c-compliant" agent skill from https://github.com/thedaviddias/Front-End-Checklist/tree/main/skills/w3c-compliant into .agents/skills/w3c-compliant/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "w3c-compliant", 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 thedaviddias/Front-End-Checklist --skill w3c-compliant -a cursorProject install goes to .agents/skills/; add -g for ~/.cursor/skills/.
$ gh skill install thedaviddias/Front-End-Checklist w3c-compliant --agent cursorProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/thedaviddias/Front-End-Checklist.git skills-src && mkdir -p .cursor/skills && cp -r skills-src/skills/w3c-compliant .cursor/skills/w3c-compliant && 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 "w3c-compliant" agent skill from https://github.com/thedaviddias/Front-End-Checklist/tree/main/skills/w3c-compliant into .cursor/skills/w3c-compliant/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "w3c-compliant", 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/thedaviddias/Front-End-Checklist.git --path skills/w3c-compliant--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 thedaviddias/Front-End-Checklist --skill w3c-compliant -a gemini-cliProject install goes to .agents/skills/; add -g for ~/.gemini/skills/.
$ gh skill install thedaviddias/Front-End-Checklist w3c-compliant --agent gemini-cliProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/thedaviddias/Front-End-Checklist.git skills-src && mkdir -p .gemini/skills && cp -r skills-src/skills/w3c-compliant .gemini/skills/w3c-compliant && 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 "w3c-compliant" agent skill from https://github.com/thedaviddias/Front-End-Checklist/tree/main/skills/w3c-compliant into .gemini/skills/w3c-compliant/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "w3c-compliant", 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 thedaviddias/Front-End-Checklist w3c-compliantInstalls 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 thedaviddias/Front-End-Checklist --skill w3c-compliant -a github-copilotProject install goes to .agents/skills/; add -g for ~/.copilot/skills/.
$ git clone --depth 1 https://github.com/thedaviddias/Front-End-Checklist.git skills-src && mkdir -p .github/skills && cp -r skills-src/skills/w3c-compliant .github/skills/w3c-compliant && 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 "w3c-compliant" agent skill from https://github.com/thedaviddias/Front-End-Checklist/tree/main/skills/w3c-compliant into .github/skills/w3c-compliant/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "w3c-compliant", 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 thedaviddias/Front-End-Checklist --skill w3c-compliant -a opencodeOpenCode documents no install command of its own. Project install goes to .agents/skills/; add -g for ~/.config/opencode/skills/.
$ gh skill install thedaviddias/Front-End-Checklist w3c-compliant --agent opencodeProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/thedaviddias/Front-End-Checklist.git skills-src && mkdir -p .opencode/skills && cp -r skills-src/skills/w3c-compliant .opencode/skills/w3c-compliant && 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 "w3c-compliant" agent skill from https://github.com/thedaviddias/Front-End-Checklist/tree/main/skills/w3c-compliant into .opencode/skills/w3c-compliant/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "w3c-compliant", 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
w3c-compliant- GitHub stars
- 74k
- Token cost
- ~421 tokens
- SKILL.md length
- 152 words
- Files
- 2 (incl. references)
- Skills in repo
- 390
- Repo updated
- First seen
- Licence
- MIT
At a glance
A skill your agent uses when reviewing templates, rendered HTML, or shared components related to Validate HTML against W3C standards.
- Reviewing templates
- SKILL.md covers Quick Reference, Check, Fix and Explain, plus 1 more section
- Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md
- Shared components related to Validate HTML against W3C standards
What it does
W3c Compliant is an agent skill from thedaviddias/Front-End-Checklist. Use when reviewing templates, rendered HTML, or shared components related to Validate HTML against W3C standards. Validate the final browser-facing markup, not just the source framework abstraction.
Its SKILL.md is about 420 tokens, which your agent loads only when the skill is triggered. The skill folder holds 2 other files, including reference files (for example `references/rule.md`).
It sits in Development. The repository describes itself as: 🗂 The essential checklist for modern web development, for humans and AI agents. The licence is MIT.
When your agent uses it
- Reviewing templates
- Shared components related to Validate HTML against W3C standards
Example prompts
- “/w3c-compliant”
What it can do on your machine
Read from SKILL.md and the folder at commit e8d14d0. 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
Links to these hosts (documentation or services it may open):
frontendchecklist.io
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
W3c Compliant loads about 421 tokens when it runs, and up to ~4.4k if it reads all its reference files. Until then it costs about 53 tokens; SKILL.md has 152 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 thedaviddias/Front-End-Checklist at commit e8d14d0, republished under its MIT licence (© thedaviddias). 152 words, ~421 tokens.
Download SKILL.mdSave it as
.claude/skills/w3c-compliant/SKILL.md (or your agent's skills folder). This skill also uses 1 other file; get the full folder from GitHub.- name
- w3c-compliant
- description
- Use when reviewing templates, rendered HTML, or shared components related to Validate HTML against W3C standards. Validate the final browser-facing markup, not just the source framework abstraction.
- metadata.category
- html
- metadata.priority
- high
- metadata.difficulty
- beginner
- metadata.estimatedTime
- 15
- metadata.source
- frontendchecklist.io
- metadata.url
- https://frontendchecklist.io/rules/html/w3c-compliant
Validate HTML against W3C standards
Invalid HTML causes unpredictable rendering across browsers, breaks accessibility tools, and makes debugging significantly harder.
Quick Reference
- Use validator.w3.org or browser extensions for validation
- Fix errors first, then warnings (errors cause rendering issues)
- Integrate validation into CI/CD with html-validate
- Common issues: unclosed tags, invalid nesting, missing attributes
Check
Validate HTML markup using the W3C HTML Validator to identify and fix markup errors that could cause cross-browser compatibility issues.
Fix
Run HTML through W3C validator and fix reported errors including unclosed tags, missing attributes, and invalid nesting.
Explain
Explain why W3C HTML validation is important for cross-browser compatibility, accessibility, and maintainable code.
Code Review
Review templates, server-rendered HTML, and shared components that output markup related to Validate HTML against W3C standards. Flag exact elements, attributes, and routes where the rendered HTML violates the rule.
For full implementation details, code examples, and framework-specific guidance,
see references/rule.md.
Rule page: https://frontendchecklist.io/rules/html/w3c-compliant
© thedaviddias, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file
Files
SKILL.md and 1 other file (references) in skills/w3c-compliant of thedaviddias/Front-End-Checklist.
- SKILL.md
- references/rule.md
Open the folder on GitHubat commit e8d14d0
Compare with similar skills
W3c Compliant 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 |
|---|---|---|---|---|---|---|
| W3c Compliant this skillthedaviddias/Front-End-Checklist | 74k | — | ~421 | Automated safety check: Pass | MIT | |
| Vercel Composition Patternssupabase/supabase | 111k | 58 repos | ~726 | Automated safety check: Pass | MIT | |
| Finishing a Development Branchobra/superpowers | 297k | 5 repos | ~1.9k | Automated safety check: Pass | MIT | |
| Typescript Advanced Typesrolling-scopes/rsschool-app | 10k | 25 repos | ~4.2k | Automated safety check: Pass | MPL-2.0 | |
| PR Babysitteropeninterpreter/openinterpreter | 69k | 3 repos | ~4.2k | Automated safety check: Pass | Apache-2.0 | |
| Code Review ChecklistshareAI-lab/learn-claude-code | 78k | 4 repos | ~1.1k | Automated safety check: Pass | MIT |
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- Official
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Walks the last step of a branch: confirm tests pass, detect the git environment, ask how to integrate, carry out your choice and clean up the worktree.
Typescript Advanced Types
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Master TypeScript's advanced type system including generics, conditional types, mapped types, template literals, and utility types for building type-safe applications.
PR Babysitter
openinterpreter/openinterpreter
Watches an open GitHub pull request until it merges, handling review comments, diagnosing CI failures and retrying flaky checks along the way.
Code Review Checklist
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Reviews code against a five-part checklist covering security, correctness, performance, maintainability and testing, and reports findings in a fixed format.
Greploop
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Iteratively improves a PR (GitHub), MR (GitLab), or shelved changelist (Perforce) until Greptile gives it a 5/5 confidence score with zero unresolved comments.
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Related
Categories
Questions about W3c Compliant
What does W3c Compliant do?
A skill your agent uses when reviewing templates, rendered HTML, or shared components related to Validate HTML against W3C standards. W3c Compliant is an agent skill from thedaviddias/Front-End-Checklist. Use when reviewing templates, rendered HTML, or shared components related to Validate HTML against W3C standards.
When should I use W3c Compliant?
W3c Compliant fits situations like: reviewing templates; shared components related to Validate HTML against W3C standards.
How do I install W3c Compliant in Claude Code?
Run `npx skills add thedaviddias/Front-End-Checklist --skill w3c-compliant -a claude-code`. Or copy the skill folder (skills/w3c-compliant in thedaviddias/Front-End-Checklist) into .claude/skills/w3c-compliant in your project. Claude Code loads it when a task matches its description.
How do I install W3c Compliant in Codex?
Run `npx skills add thedaviddias/Front-End-Checklist --skill w3c-compliant -a codex`. Or copy the skill folder (skills/w3c-compliant in thedaviddias/Front-End-Checklist) into .agents/skills/w3c-compliant in your project. Codex loads it when a task matches its description.
Can I use W3c Compliant 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 thedaviddias/Front-End-Checklist --skill w3c-compliant -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/w3c-compliant, .gemini/skills/w3c-compliant, .github/skills/w3c-compliant and .opencode/skills/w3c-compliant in your project.
What does W3c Compliant need to run?
SKILL.md names no scripts, command-line tools or credentials: W3c Compliant is instructions for the agent only.
Does W3c Compliant access the network?
SKILL.md names 1 domain. As links in the text: frontendchecklist.io. This is read from the text; nothing was executed.
Is W3c Compliant 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 W3c Compliant use?
W3c Compliant is published under the MIT licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.
How many tokens does W3c Compliant use?
About 421 tokens (SKILL.md is roughly 1.7k 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 4k tokens, read only when the agent opens those files.
What are the alternatives to W3c Compliant?
Skills that share tags, products or a category with W3c Compliant: Vercel Composition Patterns (supabase/supabase, 111k stars), Finishing a Development Branch (obra/superpowers, 297k stars), Typescript Advanced Types (rolling-scopes/rsschool-app, 10k stars) and PR Babysitter (openinterpreter/openinterpreter, 69k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.
Who maintains W3c Compliant?
thedaviddias (a GitHub user) maintains it in thedaviddias/Front-End-Checklist, which has 74,421 GitHub stars. The repository holds 390 skills in this directory. The repository was last updated on October 6, 2026.
Source: thedaviddias/Front-End-Checklist on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.