# Postbye MCP server FAQ > For AI agents: a plain-text index of this site is at https://postbye.com/llms.txt Short answers about the Postbye MCP server at https://postbye.com/mcp: what it does, whether it needs a key or a sign-in (it does not), what data comes back, which limits apply and how it relates to postbye.com. ## The basics What the server is and who can use it: ### What does the Postbye MCP server do? It lets an AI assistant look up how to cancel a subscription or membership by mail: how the company takes cancellations, the notice period, the traps to check, the mailing address on file and a ready-to-send letter. It has 4 tools: search_companies, get_cancellation_guide, get_cancellation_letter, list_categories. ### Which assistants can use it? Any client that can connect to a remote MCP server over Streamable HTTP. Set-up steps for Claude, Claude Desktop, Claude Code, Cursor, VS Code and ChatGPT are on the install page, and the clients page adds configuration for the OpenAI API and other MCP clients. - Install: /mcp-server/install - Clients: /mcp-server/clients ### What is the server URL? https://postbye.com/mcp. It is one endpoint that takes POST requests with JSON-RPC messages and answers with JSON. ### Where is it listed? In the Official MCP Registry as com.postbye/postbye, and in the discovery files /.well-known/mcp/server-card.json and /.well-known/mcp.json on postbye.com. ## Access and cost What you need before the first call: ### Do I need an API key or to sign in? No. A call with no credentials is always served: no account, API key or token is needed. Leave every sign-in field in your client empty or set authentication to none. For clients and directories that require OAuth, an optional read-only sign-in exists (see the install page); it opens the same four tools. Only a request that carries an invalid or expired Bearer token is answered with a 401. ### Does it cost anything to use? No. The server is public and free to use. ### Do I have to start a session first? No. The server keeps no sessions and sends no session id. Every request stands alone, so any client can call it at any time. ### Can a web app call it from the browser? Yes. Cross-origin calls are allowed from any origin, because the server takes no credentials and reads no cookies. ## Data and privacy What comes back and what happens to what you send: ### What data does it return? Cancellation facts for the companies Postbye has a guide for, as plain text and as structured content: - search_companies: each match's slug, category, how the company takes cancellations and the guide URL. - get_cancellation_guide: how the company takes cancellations, the notice period, the traps to check, billing-partner notes, sources, the date the facts were verified, the mailing addresses on file and the guide and address page URLs. - get_cancellation_letter: a plain-text cancellation letter and the address to send it to. - list_categories: the guide categories with the number of guides in each and the category URL. ### How does it relate to postbye.com? Every answer is built from the same company data and the same letter template as the pages on postbye.com, so the server and the site agree. Each answer carries the page URL, so you can read the same facts in a browser. ### Does it store what I type? No. Nothing you send is stored. A name or account number passed to get_cancellation_letter appears only in the letter text that comes back. ### Can it cancel, buy, mail or change anything? No. All four tools are read-only, non-destructive, idempotent and closed-world in their MCP annotations. Mailing a letter is a separate step on postbye.com. ### What happens when a company is not found? An unknown company comes back as a normal result with isError set to true and a message, so the assistant can correct itself and try again. The tools reference page shows the real answer. ## Limits What is capped: ### Is there a rate limit? The server has no keys, plans or per-user quotas, and its code applies no request throttle of its own. The limits are on the size of each request and the shape of its inputs: - Request size: up to 64 KB per request. A larger body gets HTTP 413. - Messages: one JSON-RPC message per POST. Batches are not supported. - search_companies: a query of 1 to 100 characters and at most 10 matches per call (5 by default). - get_cancellation_letter: a customer name of up to 100 characters and an account number of up to 64 characters. ### Which protocol versions does it speak? 2026-07-28, 2025-11-25, 2025-06-18, 2025-03-26, 2024-11-05. A request for any other version gets HTTP 400 with the list of supported versions. ### Are responses cached? No. Responses are sent with Cache-Control: no-store. ### Why does opening the URL in a browser show an error? https://postbye.com/mcp only accepts POST. A browser visit or any GET or DELETE request returns HTTP 405 with a short JSON description and a pointer to /mcp-server. This is expected. ## Keep reading The other documentation pages for the server: - [Postbye MCP Server for AI Assistants](https://postbye.com/mcp-server): Overview of the server: what it does, the endpoint and the four tools. - [Install the Postbye MCP Server](https://postbye.com/mcp-server/install): Set-up for Claude, Claude Code, Cursor, VS Code and ChatGPT, and how access works. - [Postbye MCP Tools Reference](https://postbye.com/mcp-server/tools): Inputs, limits and results of the four tools. - [Postbye MCP Examples](https://postbye.com/mcp-server/examples): Example prompts, tool calls with the server's real answers, and a curl request. - [Connect the Postbye MCP Server](https://postbye.com/mcp-server/clients): Steps and configuration for Claude, Cursor, VS Code, ChatGPT, the OpenAI API and other clients. ## Want the letter mailed for you? Postbye prints the letter, sends it by certified mail and emails you the signed delivery proof. [Find your company](https://postbye.com/cancel)