MCP server
for AI assistants

The Username Inspector MCP server gives AI assistants the same two tools the website has. It is a free, public Model Context Protocol server, so any assistant or agent that supports remote MCP servers can call it.

Ask your assistant whether a name is free before you rebrand a shop, or what a $60 sale really pays out on each marketplace, and it can look it up instead of guessing.

The server URL is:

https://usernameinspector.com/api/mcp

It uses the Streamable HTTP transport, needs no API key or sign-in, and keeps no session between requests.

Claude Code:

claude mcp add --transport http username-inspector https://usernameinspector.com/api/mcp

Cursor and other clients that read an mcpServers JSON config:

{
  "mcpServers": {
    "username-inspector": {
      "url": "https://usernameinspector.com/api/mcp"
    }
  }
}

Clients with a custom connector or remote server option (such as Claude's connector settings): add a new server and paste the URL above.

check_username

Looks up one username or store name on eBay, eBay Store, Poshmark, Grailed, Vinted, Whatnot, Bonanza, and Chairish, and returns a profile link for Depop, Etsy, Mercari, and Ruby Lane, which block automated checks. Poshmark, Vinted, and Bonanza most reliably return a live answer. eBay, eBay Store, Grailed, Whatnot, and Chairish often block automated lookups, and those come back as unverified with a link.

• username (required): 3 to 50 letters, numbers, hyphens, or underscores.
• platforms (optional): a list of platform ids to check. Defaults to all twelve: ebay, ebaystore, poshmark, grailed, vinted, whatnot, bonanza, chairish, depop, etsy, mercari, rubylane.

Each platform comes back as available, taken, unverified (open the returned link to check), or error, plus a summary grouped by status.

compare_fees

Compares what a sale pays out after fees on eBay, Poshmark, Mercari, Depop, Etsy, Grailed, and Vinted for US sellers, best first. It uses the same rates as the fee calculator.

• price (required): sale price in USD, before shipping.
• shipping_charged, item_cost, shipping_cost, ebay_promoted_rate_percent (all optional): add shipping, your costs, and an eBay ad rate to get profit, margin, and ROI.

Both tools are read-only. They change nothing on any platform.

• "Is vintagevault available on Poshmark, eBay, and Whatnot?"
• "I sell a jacket for $85 with $9 shipping that cost me $22. Where do I keep the most?"
• "Check whether thriftlane is free on every platform, then tell me which ones I need to verify by hand."

The server is free and runs on a small budget, so it is rate-limited to keep it available for everyone:

• About 12 tool calls per minute per client. Past that it answers with HTTP 429 and a Retry-After header.
• One username per check_username call.
• Identical lookups are cached for 5 minutes, so repeating the same check costs nothing and returns the same answer.
• Requests are capped at 16 KB and 5 messages per batch.

If you are building an agent, check each name once and read the result, rather than retrying. Limits may change, and we may turn the server off or restrict access if it is abused.

Availability comes from each platform's public profile page at the moment of the check. When a platform answers with a bot-protection challenge or an error, the tool reports unverified and gives you the link, rather than guessing. A name that reads available can still be reserved, banned, or invalid for reasons the profile page does not show, so confirm on the platform when you register.

Fee results are estimates for US sellers that exclude sales tax. Each platform's rate carries the date we last verified it. Platforms change rates often, so check the platform's own fee page before you price something.

To run a check, your assistant sends the username to our server, which looks it up on the marketplaces and returns the result. We do not store the usernames, and we do not log them. We keep only counts of tool calls with the tool name, how many platforms were checked, and how long it took. Our host, Vercel, keeps standard request logs. See the privacy policy for the rest.

Found a wrong result, a missing platform, or a tool you would like? Tell us. For a one-off check without an assistant, use the website, or see the step-by-step guide to the web tools.