WhatsApp API for developers: send, receive, track

What the API does

ChatRail gives you a workspace-scoped HTTP API for sending messages, tracking delivery state and receiving replies. Your application stays the system of record. ChatRail handles the WhatsApp connection and keeps the link between an alert, its context and the replies that follow. It is plain HTTP and JSON: no SDK is needed, and any language that can make a request works.

Send your first message

curl -X POST https://www.chatrail.dev/v1/messages/text \
  -H "Authorization: Bearer $CHATRAIL_API_KEY" \
  -H "Idempotency-Key: order-2048-dispatched" \
  -H "Content-Type: application/json" \
  -d '{"connection":"operations","to":"+14155550142",
       "body":"Order CR-2048 has shipped.",
       "context":{"order_id":"CR-2048","status":"dispatched"}}'

Use a server-side API key and a stable idempotency key. Never put credentials in browser code. The reply is 202 Accepted, which means the message is stored and queued, not that it was delivered. Delivery state arrives later on your webhook. To pair a number and send this for real, follow the quickstart.

What you can send

Send images, video, documents, audio and locations
Quote a message, mention people, send polls and contact cards
React, mark as read, edit and delete for everyone
List groups and create and manage them
Schedule a message with send_at, run recurring schedules, or check whether a number is on WhatsApp (up to 10 per request). Both are in the API reference.

What comes back

ChatRail posts signed events to the HTTPS endpoint you register. The signature is in the chatrail-signature header, with a chatrail-timestamp header beside it. Events cover inbound replies, delivery changes, connection changes, reactions, edits and poll votes.

Verify the signature before you trust an event
Receive photos, voice notes and files and download them
Match a reply to the alert it answers
Read the webhook overview or the full event reference

Delivery states

State	What it means
scheduled	Held until the send time you set.
queued	Stored and waiting to be sent.
submitted	Handed to the WhatsApp session. No confirmation yet.
sent	WhatsApp's servers accepted it.
delivered	It reached the recipient's phone.
read	The recipient opened it.
failed	It did not go through. The message carries the reason.
canceled	You canceled it before it was handed to WhatsApp.

A 202 response never means delivered. Only the message status says that. The guide on sent, delivered and read shows how to handle late and out-of-order updates.

Make every send safe to retry

Send an Idempotency-Key on every send. If a request times out, retry with the same key: you get the original response back and the customer gets one message. A repeat while the first is still running returns 409, and the same key with a different body returns 422.

Keep the connection healthy

A connection is one paired WhatsApp number. You pair it by QR code or by typing a code on the phone, and it keeps working on the phone as normal. Sessions can drop, so plan for it.

Link a number with a pairing code instead of a QR
Reconnect a dropped session

To protect the number, ChatRail refuses more than 10 messages to the same person in 5 minutes, caps group member adds at 20 an hour, and keeps an opt-out list of people who must not be messaged. When it refuses, the response says why.

Where it fits

Use ChatRail for alerts, status updates, approvals, monitoring and other workflows where the recipient may reply. It does not replace your database, your authorization system or your support process. See the tutorials for complete workflows, or browse every guide.

Limits you should understand

ChatRail connects through WhatsApp Linked Devices, not the official Meta Cloud API. Sessions can disconnect, WhatsApp controls account enforcement, and unwanted or high-risk messaging can get a number restricted. Message people who expect to hear from you, send at a steady pace, and have a plan for reconnecting. Compare it with the official API, read what working without Meta approval means and how to tell a ban from an expired session before you build on it.

What it costs

Plans are priced per connected number, not per message. The Sandbox is free with 500 messages a month. Paid plans start at $15 a month with unlimited messaging, and AI replies are included on the higher plans. See pricing for the details.

How it compares

ChatRail is not the only WhatsApp API built on Linked Devices. Each comparison goes line by line through price per number, free tier, limits, media, groups, webhooks, AI replies and MCP, using the vendor's own pricing page.

Or see all six side by side.

Frequently asked questions

Is this the official WhatsApp Cloud API?

No. ChatRail uses a linked-device session on a normal WhatsApp account.

Do I need Meta approval?

No. Pairing a number does not involve Meta business approval. Read the limits above before you build on it.

Can customers reply?

Yes. Replies, delivery changes and connection events are sent to your webhook.

Can I send to groups?

Yes. You can list groups, create them, manage members and send to a group by naming it explicitly.

Is there an SDK?

No. It is a plain HTTP API with JSON, so any HTTP client works.

Is AI required?

No. Sending, webhooks and delivery state work without AI.

A WhatsApp API for sending alerts and handling replies

Existing numbers

Event-driven

Context included