ctlogs.dev MCP server

A Model Context Protocol server for ctlogs.dev: search Certificate Transparency logs from an AI assistant or agent — subdomains, TLS certificates, organizations, CAs.

The server is hosted. There is nothing to install or run; point a client at

https://mcp.ctlogs.dev/mcp

(Streamable HTTP). It works at once without a key or an account.

Tools

Tool	What it does
find_subdomains	List the hostnames found under a domain in TLS certificates: one row per hostname with the number of certificates and first/last seen dates.
search_certificates	List TLS certificates issued for a domain name: id, matching names, issuer, serial number and validity dates.
search_organization	List TLS certificates whose subject organization matches a name, e.g. "PayPal, Inc.": id, subject common name, domains, issuer and validity dates.
get_certificate	Return the full record of one certificate: subject, issuer, serial number, validity, DNS names, key and signature details, the CT log entries that recorded it and download URLs for the certificate body.
get_ca	Return one issuing CA certificate by its SHA-256 fingerprint (the issuer_ca field of get_certificate): subject, issuer, validity, parent and cross-signed certificates, the number of certificates it issued and a page of them.

All five tools are read-only.

Connect

Claude Code

claude mcp add --transport http ctlogs https://mcp.ctlogs.dev/mcp

With a key:

claude mcp add --transport http ctlogs https://mcp.ctlogs.dev/mcp --header "Authorization: Bearer YOUR_KEY"

claude.ai

Under Customize › Connectors, choose Add, then Add custom connector, and enter the URL; under Authentication choose Sign in when needed. On Team and Enterprise plans an Owner adds it under Organization settings › Connectors.

ChatGPT

Under Plugins, choose +, then Add custom MCP server, and enter the URL.

Cursor

In ~/.cursor/mcp.json, or .cursor/mcp.json in a project:

{
  "mcpServers": {
    "ctlogs": { "url": "https://mcp.ctlogs.dev/mcp" }
  }
}

With a key:

{
  "mcpServers": {
    "ctlogs": {
      "url": "https://mcp.ctlogs.dev/mcp",
      "headers": { "Authorization": "Bearer YOUR_KEY" }
    }
  }
}

VS Code

In .vscode/mcp.json:

{
  "servers": {
    "ctlogs": { "type": "http", "url": "https://mcp.ctlogs.dev/mcp" }
  }
}

With a key:

{
  "servers": {
    "ctlogs": {
      "type": "http",
      "url": "https://mcp.ctlogs.dev/mcp",
      "headers": { "Authorization": "Bearer YOUR_KEY" }
    }
  }
}

Sign in

The server works without an account up to the anonymous limits. When a call goes past them — the hourly allowance is used up, or a list is paged further than an anonymous caller may — an assistant that supports sign-in asks you to sign in: choose GitHub, Google or an e-mail link, allow the connection, and the assistant repeats the call on your account. A new account gets a free API key with 10,000 credits a month for testing and non-commercial use. Connected assistants are listed on the account page, where each can be disconnected. Clients where you set request headers yourself can send a key instead, as shown above.

Example prompts

• Which subdomains of example.com have TLS certificates right now? Group them by what they appear to be used for.
• List the certificates issued for login.example.com and its subdomains, and tell me which certificate authorities issued them.
• Find certificates issued to the organization "Example Corp" and show me domains on them that are not under example.com.

Limits

A tool call is one API request and runs under the anonymous API's limits, or the key's plan (see limits); search_organization counts as 10, as /v1/org does. The key goes in the Authorization header only. Without a key or with a free key, a call that arrives while another is running waits up to 5 seconds for its turn. Certificate lists return 25 rows per call, limit up to 100; find_subdomains returns up to 100 hostnames per call. A list with more rows returns next_cursor for the next call.

Documentation and contact

• MCP server: https://ctlogs.dev/mcp
• API reference: https://api.ctlogs.dev/
• Keys and plans: https://api.ctlogs.dev/#auth
• Contact: contact@ctlogs.dev

This repository

It holds the connection instructions and server.json, the server's manifest in the format of the MCP Registry. The server's code is not here.

License

MIT, for the contents of this repository.