Fax API

The agent API quotes a fax, sends a PDF to one US or Canadian number, and reports whether it was delivered. The base URL is https://faxwell-api.onrender.com. An agent API and an MCP server exist. The docs for an agent are on send a fax from an AI agent.

Ask the price

GET /v1/agent/quote?to=+12125550100&pages=3 returns both tiers in cents and in USDC atomic units (USDC has 6 decimals). Add priority=true to select the priority tier in the top-level amount. The reply always lists both tiers. It does not send the fax. A bad number comes back as an error instead of a price. The written price is at /agents.txt.

Send a fax

POST /v1/agent/faxes takes JSON with to, pdf_url (an https link to a PDF) and optional priority, or a multipart upload with fields file, to and priority. priority true selects the priority tier. An optional Idempotency-Key header of 8 to 64 letters, digits, hyphens or underlines makes a retry return the same fax.

With no payment the call answers 402. The PAYMENT-REQUIRED header is the x402 v2 challenge: scheme exact, USDC, and both prices for this PDF. The first entry is the price for this request. Sign that amount and retry with the PAYMENT-SIGNATURE header. The test network is Base Sepolia (eip155:84532). Base mainnet is eip155:8453 and is off until the operator turns it on. The protocol is described at docs.cdp.coinbase.com/x402.

Or send Authorization: Bearer and a prepaid API key. POST /v1/agent/keys with {"amount_cents": 500} returns the key once and a card checkout link. The smallest top-up is $5. GET /v1/agent/balance shows what is left. The price is held when we accept the fax and taken when it is delivered.

Read the status

GET /v1/agent/faxes/{id} returns queued, sending, delivered or failed, plus the page count, the price and the last four digits of the number. Anyone with the id can read that status, so treat the id as a private link. The PDF is not in the response, and we delete it from our servers once the fax is delivered or fails.

Limits

A fax can have up to 40 pages. Callers are rate limited. One destination can receive a limited number of agent faxes per day. Premium-rate numbers and numbers outside the United States and Canada are rejected, and we do not offer a price for them.