developers / api

one API for every channel, with the agent if you want it.

The heysteff API sends and receives messages over WhatsApp (official API and QR), Instagram, Messenger, SMS and Gmail with a single integration. Signed webhooks, idempotency on every write and an OpenAPI spec that you, or your coding agent, can read.

Create an API key → Read the docs

POST /v1/messages201 Created

curl https://app.heysteff.com/api/v1/messages \
  -H "Authorization: Bearer $HEYSTEFF_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: order-1042-shipped" \
  -d '{"channel":"whatsapp_cloud","to":"+15551234567",
       "content":"Hi Ana, your order #1042 is on its way."}'

What you get

Messages and templates over WhatsApp Cloud API or QR, Instagram, Messenger, SMS and Gmail, through the same endpoint.
Signed webhooks with HMAC-SHA256, a timestamp against replays and retries with growing waits.
Idempotency: repeat a request with the same key and get the same response, never a duplicate message.
Contacts, lists, campaigns and flows over the API: sync your CRM and trigger automations from your system.
Commerce: payment link charges, refunds, attributed conversions and review requests.
For coding agents: llms.txt, llms-full.txt, AGENTS.md and an MCP server to set up the workspace with AI.

And if you want someone to answer

The API is the same one the heysteff AI agent runs on. Build everything yourself, or let the agent handle conversations and hand off to your team when needed, with copilot mode and human handoff. Your code and the agent share conversations, contacts and events.

heysteff and Kapso, honestly

Kapso is a good WhatsApp API for developers. Here is what is different:

	heysteff	Kapso
Channels	WhatsApp, Instagram, Messenger, SMS and Gmail in one API	WhatsApp
Production AI agent	Included, with copilot and human handoff	You build it with their flows
Commerce	Shopify, charges, reviews and shipment tracking	Not their focus
Docs and support in Spanish	Yes	English
OpenAPI, llms.txt and signed webhooks	Yes	Yes
SDK, CLI and sandbox	Coming soon	Available
Connect your customers' numbers	Coming soon	Available

Developer pricing

Coming soon We are preparing a per-message plan for API-only use. Today the API comes with the heysteff plans; what Meta charges for each WhatsApp message is billed separately, with no markup.

◆ next step

Create an API key and send your first WhatsApp message in five minutes.

Create an API key → Quickstart API reference

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