</> Developer API

Send faxes with one POST request

Integrate faxing into your product, back office, or workflow. Simple REST API, signed status webhooks, pay-as-you-go pricing — no subscription.

Get your API key Jump to reference

curl https://sendfax.me/api/v1/faxes \
  -H "Authorization: Bearer sfx_live_YOUR_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "to": "+15551234567",
    "file": "'$(base64 -i contract.pdf)'",
    "filename": "contract.pdf"
  }'

# → 201 Created
# { "id": "fax_ab12…", "status": "queued",
#   "pages": 3, "cost": 30, … }

API pricing

One credit balance, shared with your web account. Faxes are charged per page at the standard destination rate (10¢/page to the US) — API credit packs include bonus credit that brings your effective price down to 4¢/page. Credit never expires, and failed faxes are refunded automatically.

Starter

$10

$15 of credit — ~150 US pages

≈ 6.7¢ per US page

Growth

$50

$100 of credit — ~1,000 US pages

≈ 5.0¢ per US page

Scale

$200

$500 of credit — ~5,000 US pages

≈ 4.0¢ per US page

Authentication

Create a key in Dashboard → API and pass it as a Bearer token. Keys are shown once and stored hashed — treat them like passwords. Requests are limited to 60 per minute per key.

Authorization: Bearer sfx_live_YOUR_KEY

API reference

POST/api/v1/faxes

Send a fax. The PDF is base64-encoded in the request body (max 15 MB). Cost is computed server-side from the page count and destination rate, and charged to your balance. Returns 201 with the fax object.

{
  "to": "+15551234567",        // E.164 fax number, required
  "file": "<base64 PDF>",      // required
  "filename": "contract.pdf"   // optional
}

// 201 Created
{
  "id": "fax_ab12cd34ef56",
  "direction": "sent",
  "to": "+15551234567",
  "pages": 3,
  "cost": 30,                  // cents charged
  "status": "queued",
  "created_at": "2026-07-24T10:30:00.000Z"
}

GET/api/v1/faxes/{id}

Fetch one fax and its current status: queued → sending → delivered or failed (failed faxes are refunded and retried once automatically). Poll this, or use webhooks below.

GET/api/v1/faxes

List faxes, newest first. Query params: limit (1–100, default 25), before (ISO timestamp cursor), direction (sent or received — inbound faxes to your fax number appear here too).

{ "data": [ { "id": "fax_…", … } ], "has_more": false }

GET/api/v1/account

Your account email and current credit balance in cents.

{ "email": "you@company.com", "credit_balance": 4550 }

Webhooks

Register an https endpoint in the dashboard and we'll POST every fax lifecycle event to it: fax.queued, fax.sending, fax.delivered, fax.failed and fax.received (inbound). Deliveries are retried up to 3 times and logged in your dashboard.

// Event payload
{
  "id": "evt_9f8e7d6c5b4a",
  "type": "fax.delivered",
  "created_at": "2026-07-24T10:31:40.000Z",
  "data": {
    "fax_id": "fax_ab12cd34ef56",
    "direction": "sent",
    "to": "+15551234567",
    "pages": 3,
    "cost": 30,
    "status": "delivered"
  }
}

// Verify the signature (Standard Webhooks spec —
// works with any svix-compatible library)
import { Webhook } from "svix";

const wh = new Webhook(process.env.SENDFAX_WEBHOOK_SECRET);
const event = wh.verify(rawBody, {
  "webhook-id": req.headers["webhook-id"],
  "webhook-timestamp": req.headers["webhook-timestamp"],
  "webhook-signature": req.headers["webhook-signature"],
});

Errors

Errors return a JSON body: { "error": { "code", "message" } }

Status	Code	Meaning
401	unauthorized	Missing, invalid, or revoked API key
402	insufficient_credit	Balance too low for this fax — top up
400	invalid_number	`to` is not a valid E.164 number
400	invalid_file	File is not a readable PDF (max 15 MB)
429	rate_limited	More than 60 requests in a minute
502	carrier_rejected	Carrier refused the fax — you were not charged

Ship your fax integration today

Create a key, grab a credit pack, and send your first API fax in minutes.

Get your API key →