Model Context Protocol server
css-sota-mcp is a free, open-source MCP server that tells your coding agent which CSS features are safe to ship. Left alone the agent guesses at browser support from whatever it read in training; this one answers from live Baseline status on webstatus.dev and MDN browser-compat-data, for every property, selector and at-rule.
No key, no account. Read-only, and capped at 120 requests a minute per address — roughly ten times what an agent working through a task actually uses.
Each one answers something a developer actually asks mid-task. The agent picks by question, not by guessing at names.
“Which features exist for this, and are they safe yet?”
Search every CSS feature by keyword, Baseline status and the date it became interoperable.
Live · webstatus.dev
“What can I start using that I couldn't before?”
Everything that reached Baseline in a date window, newest first, grouped by month.
Live · webstatus.dev
“Tell me everything about this one feature.”
Baseline dates, shipping versions per browser, spec links, usage share, and the reference prose straight from MDN.
Live · webstatus.dev + mdn/content
“Which browser versions support this exactly?”
Per-browser versions for any property, value, selector, at-rule or function — including vendor prefixes and partial implementations.
Bundled · browser-compat-data
“Does this stylesheet work for my users?”
Scans real CSS and reports every feature that misses your target, with the line it's on, what's wrong, and the minimum version that would work.
Bundled · browser-compat-data
“How should this be designed — and is this page any good?”
Nielsen's heuristics, Hick and Fitts, WCAG 2.2, neurodiversity, motion, SVG craft — 37 principles to design against, and a static review that says which one a page breaks.
Bundled · UX guidelines
Any MCP client that speaks Streamable HTTP. Pick yours.
claude mcp add --scope user --transport http css-sota https://css-sota-mcp.lusrodri.workers.dev/mcp
--scope user registers it once for every project on the machine. Leave
it out and the server is added to the current project only. Then ask: “audit
src/styles.css for baseline-widely”.
Remote servers go in through Connectors, not through
claude_desktop_config.json — that file only takes local stdio servers.
Open Settings → Connectors → Add custom connector and paste the endpoint.
https://css-sota-mcp.lusrodri.workers.dev/mcpThere is nothing else to fill in: the endpoint is unauthenticated, so the connector asks for no client id and no secret.
Cloudflare's AI Playground is a hosted MCP client. Paste the endpoint, connect, and the six tools appear.
https://css-sota-mcp.lusrodri.workers.dev/mcpnpx @modelcontextprotocol/inspector@latestSet transport to Streamable HTTP and connect to the endpoint above.
Four sources, split by how fast they change. Nothing is inferred, and nothing is remembered from training.
Fetched per request · cached 1 h
Baseline status, the browser versions a feature shipped in, Web Platform Tests scores
and usage share. Behind search_css_features, whats_new and
get_feature, and never more than an hour behind the dashboard.
Compiled into the Worker
The CSS slice of MDN's compat dataset, plus the web-features catalog that
maps compat keys to Baseline features. Twenty megabytes upstream, reduced at build
time to about 1 MB of JSON — 120 KB over the wire — so
check_support and audit_css answer with no network call at
all.
Fetched per request · cached 24 h
Reference prose for get_feature, read from the Markdown source. The
canonical slug is resolved through MDN first, because compat data records the URL a
page had when the entry was written and MDN reorganises.
Compiled into the Worker
The one source here that is written rather than fetched: 37 principles behind
dont_make_me_think, drawn from Nielsen's heuristics, Hick's and Fitts's
laws, WCAG 2.2, neurodiversity research and motion practice — each with the rule, why
it holds, and what breaking it looks like in markup.
The ones worth answering before you connect anything.
css-sota-mcp is a free, open-source MCP server that tells an AI coding agent which CSS features are safe to ship. It answers from live Baseline status on webstatus.dev and from MDN browser-compat-data, so the answer reflects the web platform today rather than whenever the model's weights were frozen.
One command:
claude mcp add --scope user --transport http css-sota
https://css-sota-mcp.lusrodri.workers.dev/mcp. The --scope user
flag registers it once for every project on the machine; without it the server is
added to the current project only.
No. The hosted endpoint is public and unauthenticated — every tool is read-only over public datasets, so there is nothing to protect from disclosure. It is capped at 120 requests a minute per client address, about ten times what an agent working through a task actually uses.
Baseline is the web platform's shared vocabulary for interoperability. Widely available means a feature has worked across Chrome, Edge, Firefox and Safari — desktop and mobile — for at least 30 months. Newly available means it is interoperable across all four but became so recently. Limited availability means at least one major engine is still missing it.
Any client that speaks Streamable HTTP. It is tested against Claude Code, Claude Desktop, the Cloudflare AI Playground and the MCP Inspector — the four in the Connect section above.
Can I Use is a site a human reads, one feature at a time. This is a tool an agent
calls mid-task: hand audit_css a whole stylesheet and a target — a
Baseline level like baseline-widely, or an explicit browser list like
chrome 120, safari 17.4 — and it reports every feature that falls short,
with the line number and the minimum version that would work.
The three webstatus.dev tools fetch per request and cache for an hour, so they are
never more than an hour behind the Baseline dashboard. check_support and
audit_css read browser-compat-data and web-features compiled into the
Worker, regenerated on every build and deploy.
Yes. The whole server is one Cloudflare Worker under the MIT licence and deploys in about a minute. That is the right answer for sustained traffic above the hosted endpoint's rate limit — the repository has the steps.