Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add nathanonn/agent-skills --skill validate-block-markupgit clone --depth 1 https://github.com/nathanonn/agent-skillsWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/nathanonn/agent-skills/validate-block-markup)<a href="https://agentmods.dev/skills/nathanonn/agent-skills/validate-block-markup"><img src="https://agentmods.dev/badge/skills/nathanonn/agent-skills/validate-block-markup/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/nathanonn/agent-skills/validate-block-markup"><img src="https://agentmods.dev/badge/skills/nathanonn/agent-skills/validate-block-markup.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector warn
SkillSpector: 1 finding, up to medium
These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →
- medium MCP Rug Pull · line 17 npx commands without a version suffix (e.g. @1.0.0) create a rug-pull risk if the upstream server is compromised and publishes a malicious update.Fix: Pin the version: npx @scope/[email protected]
What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00193 | $0.02044 |
| Opus 5 | $0.00097 | $0.01022 |
| Sonnet 5 | $0.00039 | $0.00409 |
| Haiku 4.5 | $0.00019 | $0.00204 |
Grade A, and why
validate-block-markup scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 9d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 116 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Validate Block Markup
Check serialized block markup against the WordPress core block library running in Node.js. Treat structural validity and cross-site portability as separate verdicts, and treat review and repair as separate jobs.
Verdicts are produced against the core block definitions shipped with WordPress 7.0.2. Always tell the user which snapshot the verdict came from.
Requirements
- Node.js 20.10 or newer, with
npmonPATH. - First run installs a runtime into this skill's own directory:
npm ciof 350 packages, about 545 MB on disk, roughly 25 seconds, and it needs npm registry access. Later runs are offline and instant.--helpand--versionanswer immediately and install nothing. - The install never touches the user's project — no edits to their
package.json, no lockfile changes, nothing written to a project-levelnode_modules. Everything lands in<skill-directory>/node_modules/. - That distinction matters less than it sounds: the common
npx skills addlayout puts this skill inside the user's repository, so those 545 MB land in their repo tree. Say so before the first run. The skill ships a.gitignorecoveringnode_modules/and rewrites it before installing if it went missing, so git stays clean without the user doing anything. - Most of the installed bytes are
@wordpress/*packages, licensed GPL-2.0-or-later. The skill's own code is MIT. - No WordPress, PHP, wp-env, Docker, Playwright, or browser is required.
- Run validation only through
scripts/validate-block-markup.cjs. Do not import the module into your own process.
Dependency Bootstrap
The executable bootstraps itself. Before loading the validator it checks <skill-directory>/node_modules/ for four pinned packages and, if any is absent or at a different version, runs this in the skill directory:
npm ci --omit=dev --ignore-scripts --no-audit --no-fund
| Package | Pinned version |
|---|---|
@wordpress/blocks |
15.13.1 |
@wordpress/block-library |
9.40.2 |
@wordpress/block-serialization-default-parser |
5.40.1 |
jsdom |
26.1.0 |
What ships with it
8 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 9d ago First seen · 116 lines · 193 tokens per session scan A 75f709f7aae6
validate-block-markup is a skill published in the GitHub repository nathanonn/agent-skills (19 stars, last pushed 20d ago), licensed MIT. It adds 193 tokens to every session and 2,044 once invoked, about $0.0010 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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