validator

Swatchdog MCP Server

Give your AI agent a visual system to build against — so it writes brand-consistent styles instead of guessing colors, radii, spacing, and type.

✅ Now in the Anthropic Connector Directory. In Claude, open Settings → Connectors, search swatchdog, and click Connect — no URL, no key, no setup.

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See it in action

• Live claude.ai run: connector session walkthrough →
• Full test transcript (all green): part-b-transcript.txt →

https://github.com/user-attachments/assets/6ae8b242-d6c7-4a29-8892-27b067835308

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What it is

Swatchdog is a Model Context Protocol (MCP) server that runs on-demand design-token drift checks for AI coding assistants — Claude Code, Claude Desktop, Cursor, Google Antigravity, other MCP clients, and claude.ai via the connector.

When your agent asks, Swatchdog checks the generated CSS against a design system — a curated pack or your own tokens — and returns every off-token color, radius, spacing, and type value, each with the closest matching token to use instead. The check is on-demand and the loop is yours: Swatchdog reports drift; it never intercepts writes or changes your code.

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Why Swatchdog

AI agents are fast but blind to your design system — they invent off-brand spacing, off-palette colors, and quietly ignore your scales. Swatchdog adds a deterministic drift check to the build loop:

1. The agent sets a standard — your own tokens, or a pack.
2. It calls Swatchdog on the CSS it generated.
3. Swatchdog returns precise fixes (e.g. "use radius.sm (5px) instead of 7px").
4. The agent applies them. The loop, and the review, stay yours.

How is it different from a linter like ESLint? A linter checks whether your code is valid; Swatchdog checks whether your design is on-system. A linter happily passes color: #ff00ff because it's valid CSS — it has no idea magenta isn't in your palette. Swatchdog catches exactly that, even when the code is flawless. Lint catches broken code; Swatchdog catches broken design.

Can't I just give my agent the tokens, or a design.md? You can, and it'll still drift. Agents approximate and interpolate even with the rules right in front of them — having the rules isn't the same as following them. Swatchdog verifies conformance in the build loop, where the drift actually happens.

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Modes

Pack mode — check against a curated Swatchdog family (Workbench, Showcase, Terminal, plus the free Studio sandbox). Zero-config.

BYO mode — check against your own design system. The agent extracts your tokens (from tailwind.config.js, CSS variables, etc.) and passes them as parameters. Content-only and stateless — your code and tokens are never stored. Free to try on the keyless connector lane, or uncapped with a $12 license.

Intelligent suggestions — Swatchdog doesn't just flag drift, it maps each off-token value to the nearest valid token: color (hex/rgb → nearest theme color), radius, spacing, font-size, and font-family.

Coverage note: checks currently cover hex and standard color formats. HSL-channel representation and complex multi-file token resolution are on the Phase 2 roadmap.

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Tools

check_design_drift — connector endpoint · BYO-only · keyless-friendly

• reference_tokens (object, required) — your design tokens, e.g. {"color":{"primary":"#b06ed0"},"radius":{"md":"6px"}}
• code (string, required) — the CSS/markup to check
• Returns, per violation: axis · found value · expected token + value · location

check_drift — main endpoint · checks CSS against a pack or a custom token set

• content (string, required) — the CSS/markup to check
• paletteId (string, optional) — a pack id (e.g. studio-blue-hour); pack mode
• tokens (object, optional) — your own token set; BYO mode
• source (string, optional) — telemetry tag (pack, css, tailwind)

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Pricing — one-time, no subscriptions

Tier	What you get	Where
Free — keyless	BYO checks on a shared, rate-capped lane	connector endpoint
Free — sandbox key swt_sandbox_studio	pack checks vs the Studio family	main endpoint
$12 — drift-check license	BYO checks, your own uncapped key	both endpoints
$19 / $49 — pack or bundle	premium families (Workbench · Showcase · Terminal) + a paid key	both endpoints

On the main endpoint, a free caller attempting a premium or BYO check gets a structured upgrade payload pointing to swatchdog.dev.

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Connect

In Claude (easiest): Settings → Connectors → find swatchdog in the directory → Connect. Nothing to paste, no key.

Other MCP clients (Cursor, Claude Code, Claude Desktop) — add one of these to your MCP config:

Connector endpoint — BYO-only, keyless (add a key to remove the rate cap):

{
  "mcpServers": {
    "swatchdog-check": {
      "type": "http",
      "url": "https://swatchdog-connector-970396648818.us-central1.run.app/mcp"
    }
  }
}

Main endpoint — packs + BYO, bearer key (free sandbox key shown):

{
  "mcpServers": {
    "swatchdog-sandbox": {
      "type": "http",
      "url": "https://swatchdog-mcp-970396648818.us-central1.run.app/mcp",
      "headers": { "Authorization": "Bearer swt_sandbox_studio" }
    }
  }
}

Prefer to add the connector to claude.ai manually? Settings → Connectors → Add custom connector → paste the connector URL above → leave auth empty.

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Privacy

All checks are on-demand and transient. No source code, files, or tokens are ever stored on our servers. We log only minimal usage metadata — a source tag, which pack, and the finding count — never your license key, your code, or your tokens. Full policy: swatchdog.dev/privacy.html.

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Created and maintained by swatchdog.dev · Support: [email protected] · A Ziola Project