Build call, SMS and chat features
on the Hello by Flow API.

The Hello by Flow API powers a multi-tenant cloud calling platform: external Twilio voice and SMS, free internal team chat, peer-to-peer WebRTC meetings, and an admin console for managing customer organizations. Production-ready, REST, OpenAPI 3.1.

Quickstart

Three steps to your first API call. Use the demo credentials below, or grab your own from /signup.

1. 1

   Authenticate

   cURLcopy

   curl -X POST https://hellobyflow.com/api/auth/login \
     -H "Content-Type: application/json" \
     -d '{"email":"admin@hellobyflow.com","password":"admin123"}'

2. 2

   Make your first call

   cURLcopy

   curl -X POST https://hellobyflow.com/api/calls/start \
     -H "Authorization: Bearer $TOKEN" \
     -H "Content-Type: application/json" \
     -d '{"to_number":"+13072402137","to_name":"Hana Park","direction":"outbound"}'

3. 3

   Send your first SMS

   Python (SDK)copy

   from hellobyflow import HelloByFlowClient
   
   client = HelloByFlowClient(base_url="https://hellobyflow.com")
   client.login(email="you@example.com", password="your-password")
   
   client.send_sms(body={"to_number": "+13072402137", "body": "Hello!"})

   TypeScript (SDK)copy

   import { HelloByFlowClient } from "@hellobyflow/sdk";
   
   const client = new HelloByFlowClient({ baseUrl: "https://hellobyflow.com" });
   await client.login({ email: "you@example.com", password: "your-password" });
   
   await client.sendSms({ body: { to_number: "+13072402137", body: "Hello!" } });

Authentication

Every protected endpoint accepts two equivalent auth schemes. Pick whichever fits your runtime — the server treats them identically.

Roles

Official SDKs

Both SDKs are auto-generated from the same OpenAPI spec the server publishes — they regenerate on every backend boot, so they never drift from the API.

curl -L -o hbf-sdk-python.tar.gz https://hellobyflow.com/api/developers/sdk/python.tar.gz
tar xzf hbf-sdk-python.tar.gz
cd hbf-sdk-python && pip install -e .

curl -L -o hbf-sdk-typescript.tar.gz https://hellobyflow.com/api/developers/sdk/typescript.tar.gz
tar xzf hbf-sdk-typescript.tar.gz
cd hbf-sdk-typescript && npm install && npm run build

Need a Ruby, Go, or PHP client? Feed the OpenAPI spec into openapi-generator-cli or your favorite generator — the spec has rich tags, summaries, and examples ready.

Postman Collection

One-click collection with every endpoint pre-organized by tag. Set the email and password environment variables once — the included pre-request script auto-fetches an access token before every request.

Webhooks

Hello by Flow exposes Twilio's standard callback endpoints so you can self-host PSTN routing. All webhook URLs are public (no auth) — Twilio signs requests with X-Twilio-Signature; we verify it via providers/twilio.validate_signature().

Pointing your own Twilio account at these URLs? Replace hellobyflow.com with your custom subdomain.

API Reference

The full operation reference — every endpoint with examples, response schemas, and a "Try it out" button.

Errors & Status Codes

Every error uses the same JSON envelope:

{ "detail": "Admin only" }

Rate Limits & Lockout

We don't currently enforce a global request quota. Two specific protections are in place:

• Login lockout: 5 failed attempts on the same identifier triggers a 15-minute cooldown returning 429.
• Attachment uploads are capped at 25 MB per file (413 if exceeded).

Need higher limits? Email partners@hellobyflow.com.

Support

Stuck on an integration? Two ways to reach us — both real humans.