Send a fax from an AI agent
An agent can send a fax by calling three tools on the FaxFair MCP server, or by calling the HTTP API. The fax goes to a number in the United States or Canada.
MCP server
The server is remote and speaks streamable HTTP at https://faxwell-api.onrender.com/mcp. After initialize, the session id comes back in the Mcp-Session-Id header. The tools are quote_fax (number, page count and optional priority, no charge), send_fax (number, an https link to the PDF and optional priority) and get_fax_status (the id from send). A registry manifest lives with the server code as server/mcp/server.json.
How the agent pays
For one fax and no account, the agent pays in USDC on Base using the x402 protocol. send_fax with no payment answers HTTP 402 and a PAYMENT-REQUIRED header that lists both tiers. The agent signs the price for this request and calls the tool again with PAYMENT-SIGNATURE. Pass priority true for the priority tier. The written price is at /agents.txt. The test network is Base Sepolia. See the API page for the fields.
For many faxes, create a prepaid key with POST /v1/agent/keys and a card checkout of at least $5, then send Authorization: Bearer on later calls. The key is shown once. If the fax fails, an API key gets the hold back, and a USDC payment becomes credit for that wallet on the next fax.
Questions
How do I send a fax from an AI agent?
Connect the agent to the FaxFair MCP server at https://faxwell-api.onrender.com/mcp, or call POST /v1/agent/faxes with the fax number and an https link to the PDF. The tools are quote_fax, send_fax and get_fax_status.
How much does an agent pay to send a fax?
The quote and the HTTP 402 return the price for that fax. The written price is at https://faxfair.com/agents.txt. One page is the smallest charge. A priority fax is sent before other agent faxes. A fax from the website or the app is still sent first. Payment is USDC on Base for that single call, or a prepaid API key funded by card.
Which fax numbers can an agent dial?
United States and Canadian fax numbers, including US territories. Premium-rate numbers such as 900 and 976 are rejected, and so are numbers in other countries, because those routes are not priced.
People sending from a browser can follow how to send a fax online. Prices for the website and the app are on the pricing page.