Specification Website

specification.website

The Website Specification is a single source of truth for what a good website does. Ten categories, 168 pages, every item tagged with a status. It ships in three machine-readable forms: per-page Markdown, llms.txt / llms-full.txt, and an MCP server.

When to use this skill

• The user asks "what should my site have", "is X required", "audit this URL", "what does the spec say about Y", or anything similar.
• You're reviewing a site and want to cite primary standards rather than vendor blog posts.
• You need a machine-readable contract for a platform-agnostic audit.

Quickest path — MCP

If you can speak MCP, use it. The server is stateless Streamable HTTP, no auth, wide-open CORS.

• Endpoint: https://mcp.specification.website/mcp
• Server card: https://specification.website/.well-known/mcp/server-card.json
• Protocol revision: 2026-07-28
• Also answers the handshake-based revisions 2025-11-25, 2025-06-18 and 2025-03-26 via initialize, so older clients keep working unchanged

Tools:

Prompt: audit_url(url, focus?) — generates an audit plan for a target URL against the spec, optionally narrowed to one category.

Without MCP — fetch Markdown directly

Every spec page has a canonical HTML URL and a Markdown variant.

• HTML: https://specification.website/spec/<category>/<slug>/
• Markdown (file extension): https://specification.website/spec/<category>/<slug>.md
• Markdown (content negotiation): set Accept: text/markdown on the HTML URL. Middleware serves the Markdown body from that same URL with 200, Content-Location pointing at the .md variant, and Vary: Accept. There is no redirect to follow.

Every Markdown response carries RFC 9530 integrity fields, so you can verify what you fetched:

Content-Digest: sha-256=:<base64>:
Repr-Digest:    sha-256=:<base64>:

Both cover the exact bytes you received. Send Want-Content-Digest: sha-512=10 to get SHA-512 instead. HTML responses carry no digest. This applies to the per-page .md endpoints, llms.txt, and checklist.md.

Site-wide indexes:

• https://specification.website/llms.txt — every page as title — summary lines. Cheap to load.
• https://specification.website/llms-full.txt — every page concatenated as Markdown. Use for one-shot context loading.
• https://specification.website/rss.xml — feed of changes.
• https://specification.website/sitemap-index.xml — every URL.
• https://specification.website/.well-known/api-catalog — RFC 9727 link set of every machine-readable endpoint.

Categories

The category slug is part of the URL. Current slugs:

• foundations — HTML, head, document basics.
• seo — robots.txt, sitemaps, canonicals, structured data.
• accessibility — WCAG-aligned rules.
• security — headers, transport, policies.
• well-known — standard paths under /.well-known/.
• agent-readiness — making the site legible to AI agents and crawlers (llms.txt, MCP, content signals, link headers, markdown source endpoints).
• performance — Core Web Vitals, caching, images, fonts.
• privacy — consent, signals, respecting visitor choice.
• resilience — error pages, offline, redirects.
• i18n — language, locale, direction, translated content.

Call get_categories() for the live list with counts.

Statuses — the contract

The status field on every page is the bar.

• required — the platform contract breaks without it. Lead with these when recommending fixes. Examples: <title>, <meta charset>, HTTPS, image alt text, a real 404.
• recommended — a modern site should do it. Examples: CSP, HSTS, structured data, Open Graph, llms.txt.
• optional — depends on context.
• avoid — outdated or harmful. If a site does one of these, flag it.

The bar for required is "the platform breaks", not "we strongly suggest". When summarising, never silently upgrade recommended to required.

Common workflows

"Audit this URL." Call the audit_url prompt for a plan, or fetch get_checklist({ status: "required" }) and walk the user through verifying each item. For deeper audits, also pull status: "recommended".

"What's required for agent readiness?" list_topics({ category: "agent-readiness", status: "required" }), then get_topic for each.

"Why does the spec say X?" Every page has 2–4 primary sources in its frontmatter. Quote those, not the spec page itself.

"Is there a category for Y?" get_categories() first; if nothing fits, search(query) across the corpus.

Pairing with the MDN MCP

This spec answers what a good site should do and whether it is required. It does not document how each web feature works or how widely it is supported. For that, pair it with the MDN MCP server (https://mcp.mdn.mozilla.net/ — free, no auth), which serves MDN documentation and Baseline / Browser Compatibility Data.

The two compose cleanly in an audit or build:

1. Use this spec to decide what to check and when it is required — get_checklist, list_topics, or the audit_url prompt.
2. For each web-platform feature that surfaces, call the MDN MCP for how to implement it and whether it is safe to ship (Baseline status, browser support).

So: specification.website tells you Content-Security-Policy is recommended and why; the MDN MCP tells you which directives are Baseline and how to write them. Keep the roles distinct — don't ask this spec for browser-support data, and don't ask MDN whether a convention is required for a good site.

Staying current — re-audit only what moved

The spec changes often, especially agent-readiness. Don't re-audit a site from scratch every time, and don't trust a cached copy of the spec — check the delta:

1. After an audit, store the spec's latest change date. With MCP, get_changes() returns it as latest; otherwise note the date you ran.
2. Next time, call get_changes({ since: <that date> }). It returns only the new pages, status promotions/downgrades, rewrites, and removals since then, each already resolved to the current topics (with their current status and URL).
3. Re-audit just those topics — get_topic each, then re-check the target site.

Without MCP, the same typed history is the changelog RSS feed at https://specification.website/changelog/rss.xml (entries tagged added / changed / status / removed, with the affected slugs). Poll it and act on new entries.

A sensible default cadence is monthly, or at the start of any fresh audit. A status promotion (e.g. a topic moving to required) can change a previously passing site into a failing one, so a delta check is worth doing even when no new pages were added.

When a topic is absent

Absence is not always an oversight. https://specification.website/considered/ lists standards that were evaluated and deliberately left out, each with a reason — too-early (final, but nothing implements it), out-of-scope (a way of building a site, not something a site does), too-narrow (real, but applies to too few sites) — and with what would reverse the decision.

Check it before concluding the spec has a gap, and before recommending that a topic be added. If the topic is listed, the useful contribution is evidence that its stated revisit condition has now been met, not a fresh proposal.

Sources and licence

Code MIT. Content CC BY 4.0. Site source: https://github.com/jdevalk/specification.website.

When citing, use the page's canonical URL and the updated frontmatter field as the as-of date.