CheckFitment for AI assistants

CheckFitment runs one public MCP server (Model Context Protocol) with the same maths and vehicle dataset as this site: bolt patterns and wheel specs by vehicle, wheel and tire fitment, tire size changes and speedometer error, wheel spacers and gear ratios. It needs no account, no login and no personal data.

Where you can use it

• ChatGPT: add the CheckFitment app from the ChatGPT apps directory.
• Claude (claude.ai, Claude Desktop, Claude Code): search for CheckFitment in the Connectors directory, or add it as a custom connector: Settings → Connectors → Add custom connector → paste https://checkfitment.com/mcp?src=claude. No authentication.
• Gemini: where your Gemini plan offers custom apps, add https://checkfitment.com/mcp?src=gemini as the server URL.
• Any other MCP client (Cursor, VS Code, Codex and others): use the endpoint below. The server is also listed in the official MCP Registry as com.checkfitment/checkfitment.

Endpoint

Transport: MCP Streamable HTTP, stateless JSON-RPC 2.0 over HTTPS POST. No sessions, no authentication, no API key. CORS is open. Server version 1.1.0.

https://checkfitment.com/mcp

The optional src query parameter names the client (chatgpt, claude, gemini, gworkspace or mcp). It only tags the links the server returns, so we can see which assistant brought a visitor. It changes nothing else.

Example configuration for a client that reads a JSON settings file:

{
  "mcpServers": {
    "checkfitment": {
      "type": "streamable-http",
      "url": "https://checkfitment.com/mcp?src=mcp"
    }
  }
}

Quick test from a terminal:

curl -s -X POST https://checkfitment.com/mcp \
  -H 'Content-Type: application/json' \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/list"}'

Tools

All tools are read-only (readOnlyHint: true) and never call anything outside this site. Every answer carries a short text with a link to the matching page here and a structuredContent object that matches the tool's output schema. A vehicle that is not in the dataset is reported as not found, never guessed. The answers show no prices and no shop or affiliate links.

bolt_pattern_lookup: Vehicle bolt pattern and wheel specs

• make (string, required): e.g. Ford, Toyota, Jeep
• model (string, required): e.g. F-150, Tacoma, Wrangler
• year (integer)
• wheel_center_bore_mm (number): Optional: center bore of a wheel you want to check against the hub.

wheel_fitment_check: Will these wheels (and tires) fit

• current_wheel_width_in (number, required)
• current_offset_mm (number, required)
• current_tire (string): Current tire size. Metric like 265/70R17 (P or LT prefix allowed) or flotation like 33x12.50R17; no load index or speed rating.
• new_wheel_width_in (number, required)
• new_offset_mm (number, required)
• new_tire (string): New tire size. Metric like 265/70R17 (P or LT prefix allowed) or flotation like 33x12.50R17; no load index or speed rating.
• outer_clearance_mm (number): Measured on the current setup: tire sidewall to fender lip.
• inner_clearance_mm (number): Measured on the current setup: inner sidewall to the nearest suspension or body part.

tire_size_compare: Tire size change: diameter and speedometer

• old_tire (string, required): Factory or current tire. Metric like 265/70R17 (P or LT prefix allowed) or flotation like 33x12.50R17; no load index or speed rating.
• new_tire (string, required): New tire. Metric like 265/70R17 (P or LT prefix allowed) or flotation like 33x12.50R17; no load index or speed rating.
• speed_shown (number): Speedometer reading to convert (default 60).

wheel_spacer_calculator: Wheel spacer size and stud engagement

• offset_mm (number, required): Offset (ET) of the wheel.
• target_offset_mm (number)
• spacer_mm (number)
• stud (string)
• stud_protrusion_mm (number): Stud length past the hub face.
• wheel_pad_thickness_mm (number): Thickness of the wheel mounting pad.

gear_ratio_calculator: Gear ratio after a tire change, regear

• old_tire (string, required): Factory tire. Metric like 265/70R17 (P or LT prefix allowed) or flotation like 33x12.50R17; no load index or speed rating.
• new_tire (string, required): New tire. Metric like 265/70R17 (P or LT prefix allowed) or flotation like 33x12.50R17; no load index or speed rating.
• axle_ratio (number, required): Current axle (differential) ratio, e.g. 3.73.
• speed_mph (number): Road speed for the RPM figures (default 65).
• transfer_case_low_ratio (number)
• first_gear_ratio (number)

bolt_pattern_facts: Bolt pattern in mm and inches, look-alikes

• pattern (string, required): 5x114.3, 5x4.5, 6x139.7, 8x6.5 …

Accuracy and privacy

Vehicle figures come from the CheckFitment dataset, each marked verified or unverified as explained in how we verify. Results are estimates for planning: check them against your vehicle before you buy or fit anything (see the terms). What the server receives and what it keeps is described in the privacy policy.

Contact

Questions or a bug in an answer: info@checkfitment.com