MCP server

Domduck's MCP server is one of the three surfaces the product ships: a dashboard for people, an MCP server for agents, and an embeddable badge for other people's pages.

• Endpoint POST https://domduck.com/api/mcp
• Transport Streamable HTTP. Every answer is the response to a POST; this server never opens a stream.
• Authentication Authorization: Bearer ddk_.... Create a key at https://domduck.com/settings/api-keys.
• Rate limit 240 requests a minute, per key.
• Scope Every tool answers for the account that owns the key, and only for domains that account already tracks.

There is also a public server with three read-only tools and no key at all.

Connect

Claude Code

claude mcp add --transport http domduck https://domduck.com/api/mcp \
  --header "Authorization: Bearer ddk_YOUR_KEY"

Cursor, VS Code, and any client with an mcp.json

{
  "mcpServers": {
    "domduck": {
      "type": "http",
      "url": "https://domduck.com/api/mcp",
      "headers": { "Authorization": "Bearer ddk_YOUR_KEY" }
    }
  }
}

Claude Messages API

{
  "mcp_servers": [
    {
      "type": "url",
      "url": "https://domduck.com/api/mcp",
      "name": "domduck",
      "authorization_token": "ddk_YOUR_KEY"
    }
  ],
  "tools": [{ "type": "mcp_toolset", "mcp_server_name": "domduck" }]
}

Send the beta header anthropic-beta: mcp-client-2025-11-20 with that request.

Raw JSON-RPC

curl -s https://domduck.com/api/mcp \
  -H "Authorization: Bearer ddk_YOUR_KEY" \
  -H "content-type: application/json" \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/list"}'

Protocol

This server answers both protocol eras on one endpoint.

Which era a request is in is decided by the body, not the header. A request with no _meta version is legacy even when it sends MCP-Protocol-Version, because that header existed in 2025-06-18 too.

server/discover is implemented and answers on both paths, with or without _meta, so a probe does not have to know the era first.

Modern requests get the status codes that revision requires: 400 with -32022 for a version this server does not implement, 400 with -32020 when a header disagrees with the body, and 404 with -32601 for an unknown method. Legacy requests answer 200 throughout.

Errors

A tool that fails returns a normal result with isError: true and a plain sentence, not a JSON-RPC error. That is deliberate: a model can fix its own arguments and retry, and it cannot fix a protocol error. Read the message.

{
  "jsonrpc": "2.0",
  "id": 2,
  "result": {
    "content": [
      {
        "type": "text",
        "text": "stripe.com is not tracked by this account. Use add_domain first, or list_domains to see what is."
      }
    ],
    "isError": true
  }
}

A domain this account does not track is always reported as untracked, never as non-existent. The distinction would turn this endpoint into a way to ask what other people are watching.

Tools

A worked call

curl -s https://domduck.com/api/mcp \
  -H "Authorization: Bearer ddk_YOUR_KEY" \
  -H "content-type: application/json" \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/call",
       "params":{"name":"get_history",
                 "arguments":{"domain":"stripe.com","source":"ahrefs_dr","days":30}}}'

The result's content[0].text is JSON as a string, which is how MCP carries a structured answer:

{
  "domain": "stripe.com",
  "source": "ahrefs_dr",
  "days": 30,
  "higherIsBetter": true,
  "points": [
    { "day": "2026-07-05", "value": 95 },
    { "day": "2026-07-06", "value": null },
    { "day": "2026-07-07", "value": 95 }
  ]
}

**null is a day with no reading, and it is not a zero.** Nobody looked that day. A zero is a value a domain can hold, and on a rank series where lower is better, reading a gap as zero turns every gap into the best result ever recorded. Draw a gap, not a point.

list_domains

Every domain this account tracks, with its latest Domain Rating, Tranco rank, tags and observation count. The place to start: most other tools take a domain from this list.

get_domain

The latest reading from every source for one tracked domain: Domain Rating, Tranco rank, registration date, TLS certificate, DNS, AI crawler policy. Includes how many days of history exist per source and any recent source failures.

get_history

One reading per day for a domain and source, oldest first. This is what the product is for: the series cannot be obtained anywhere else and cannot be backfilled. A null value is a day with no reading, which is a real state and not a zero.

get_ai_crawler_policy

Which of the eight tracked AI crawlers a domain's robots.txt admits, and whether it publishes an llms.txt. Three states per agent: allowed, disallowed, unspecified. Unspecified is NOT allowed, because a catch-all Disallow blocks an agent the file never names, so read effective for what is actually in force. Reads the last stored reading; it does not fetch the file.

add_domain

Add a domain to this account and immediately read every cheap source once, so it has values rather than dashes. Unlimited domains, no tier cap. Re-adding one already tracked is a no-op that still refreshes it.

remove_domain

Take a domain off this account. Its observation history is NOT deleted: it keeps accumulating and comes back intact if the domain is added again. Only the list changes.

check_domain

Re-read every cheap source for one tracked domain right now, instead of waiting for the daily sweep. Use it after a change that should move a number, not as a polling loop: the metrics move over weeks.

set_domain_flags

Change how a tracked domain is filed. Pausing keeps the domain and its history but drops it out of the daily sweep. Omitted fields are left alone.

list_tags

This account's tags with the number of domains carrying each. Tags are per-user and a domain can hold several. Takes no arguments.

list_sources

What Domduck reads and what each source means, including the eight AI crawlers whose robots.txt policy is tracked. Useful for interpreting get_domain output without guessing at field names. Takes no arguments.