css-check-compat

css-check-compat is a command for coding agents from lesleslie/css-mcp. It costs 17 tokens per session (338 once invoked), scanned A, original, BSD-3-Clause.

A command that checks whether CSS properties work across Chrome, Firefox, Safari, and Edge, using browser-compatibility data and MDN, the Mozilla documentation site.

In plain words
What is it for?
Use it to check properties such as `container-type` or `subgrid`, choose target browsers, and find documentation about caveats and fallback approaches.
Why use it?
It helps catch browser support gaps before a CSS feature breaks or behaves differently for users. It also clarifies misspelled properties and explains partial or unknown support.

Command

Part of the css plugin — 3 commands shipped together

Install

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.

agentmods
npx agentmods add commands/lesleslie/css-mcp/css-check-compat
Clone the repo
git clone --depth 1 https://github.com/lesleslie/css-mcp

Or install css, the plugin that ships this one along with the rest of its 3 commands.

Wrote 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.

agentmods badge for css-check-compat

README.md
[![agentmods](https://agentmods.dev/badge/commands/lesleslie/css-mcp/css-check-compat.svg)](https://agentmods.dev/commands/lesleslie/css-mcp/css-check-compat)
Your own site
<a href="https://agentmods.dev/commands/lesleslie/css-mcp/css-check-compat"><img src="https://agentmods.dev/badge/commands/lesleslie/css-mcp/css-check-compat.svg" alt="Measured on agentmods" height="20"></a>
Per session 17 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 338 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5 $0.00017 $0.00338
Opus 5 $0.00009 $0.00169
Sonnet 5 $0.00003 $0.00068
Haiku 4.5 $0.00002 $0.00034

Measured 3d ago against content hash 807362c596b1, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

css-check-compat 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 3d 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.

commands/css-check-compat.md · 25 lines

What it actually says

/css-check-compat

Verify cross-browser support for one or more CSS properties and follow up with MDN documentation when the result is partial or unknown.

Usage

/css-check-compat <property> [<property> ...] [--browser chrome,firefox,safari,edge]

What it does

  1. Calls mcp__css__list_capabilities to confirm the server is healthy and to surface the canonical property list (used to disambiguate user typos).
  2. If a property name does not appear in the canonical list, falls back to mcp__css__search_properties for a fuzzy match and presents the closest candidates before proceeding.
  3. Calls mcp__css__get_browser_compatibility with the resolved property names plus the requested target browsers (defaults: chrome, firefox, safari, edge).
  4. For any property the compatibility report marks as partial or unknown, follows up with mcp__css__get_docs so the user gets the relevant MDN context (baseline support, caveats, fallback strategies) in the same response.

Example

/css-check-compat container-type subgrid --browser chrome,firefox,safari

Changes

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.

  1. 3d ago First seen · 25 lines · 17 tokens per session scan A 807362c596b1

Subscribe to this mod's changes

css-check-compat is a command published in the GitHub repository lesleslie/css-mcp (1 stars, last pushed 5d ago), licensed BSD-3-Clause. It adds 17 tokens to every session and 338 once invoked, about $0.0001 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 2026-08-31.