What is a fax API, and when should you use one?
August 23, 2026 · 5 min read
A fax API lets software send and receive faxes without a human clicking anything. Instead of opening an app, your application makes an API call to send a document, and receives a webhook when a fax arrives. It is how you build faxing into an EHR, CRM, or back-office system.
What a fax API does
At minimum: send a fax (you POST a document and a destination number), receive inbound faxes (the service calls your webhook with the document and metadata), and report delivery status (callbacks for queued, sending, delivered, or failed). Better APIs add automatic retries, signed webhooks, and idempotent handling so your integration is reliable at volume.
Common use cases
Automatically fax invoices, orders, or signed forms from your app. Capture inbound faxes into your system of record without manual filing. Trigger a workflow the instant a document arrives. In healthcare, send prescriptions or referrals and ingest the responses programmatically.
The feature that changes everything: data extraction
Most fax APIs stop at moving a PDF. The bigger win is getting structured data back. With data extraction (Faxday calls this Smart Fax), an inbound form comes back as fields your code can use — matched to the originating request — so a faxed form updates a record automatically instead of a person re-typing it.
What to look for
Reliable delivery classification and retries, signed and idempotent webhooks, clear JSON, good docs, and — if you handle PHI — a signed BAA with audit logging. If your documents are forms, prioritize an API that returns structured data, not just the PDF.