voiceOne API — open, documented, ready.
REST + GraphQL API. Webhooks for call, appointment and CRM events. SDKs for Node.js, Python, PHP, Go. Developer portal with sandbox, OpenAPI spec and Postman collection. Included in the voiceOne plan — even in the 14-day trial.
Why an open voiceOne API?
Because your stack doesn't stop where voiceOne begins. And because vendor lock-in is an anti-feature.
REST + GraphQL
Classic REST for standard integrations. GraphQL for more complex queries with selection. Both endpoints with the same authentication.
Webhooks for events
Call start, call end, appointment booked, lead captured, CRM update, sentiment trigger. We POST, you process. Retries with exponential backoff.
Official SDKs
Node.js, Python, PHP, Go, .NET (Beta). Fully type-safe, with test coverage, published to npm/PyPI/Composer/Go Mod.
Free sandbox
Develop against the sandbox endpoint before going live. Test phone number, test webhooks, all endpoints — without it costing a cent.
What the API can do
Fully modular: what you need, without a mandatory package.
Initiate, read, edit calls
Start an outbound call, read live status, receive the audio stream live, end a call, retrieve a recording.
- Web Real-Time Audio (WebRTC)
- Outbound with caller-ID selection
- Live transcript stream
Push instead of pull
20+ event types subscribable per URL. Filters per tenant / sector. Retries 5x with backoff. Signature verification HMAC-SHA256.
- Selective event subscription
- Custom headers
- Audit log for webhooks
Contacts, pipelines, tasks
CRUD on contacts, companies, deals, tasks. Bulk operations up to 5,000 items. Custom fields are typed correctly.
- JSON-Schema validated
- Cursor-based pagination
- Soft delete + audit log
Appointments programmatically
Check availability, reserve slots, confirm appointments, trigger reminders. Multi-calendar per account.
- Time-zone-aware (IANA)
- ICS output
- Conflict detection
No-code configuration
In the voiceOne portal: choose an event, enter a URL, optionally set filters, live test. No code, no effort.
- Filters with DSL ("if branche=praxis")
- Header & body transform
- Replay function for tests
WebRTC live stream
Receive / send live audio of the call. For your own voice bots, quality monitoring, real-time coaching.
- Opus & PCM format
- Bi-directional
- VoIP codec-converted
voiceOne API vs. Twilio vs. Vonage
An honest comparison. Twilio is the reference for telephony APIs. We play in a different league: voiceOne is AI assistant + API.
| Feature | voiceOne | Twilio Voice + AI | Vonage Voice + AI |
|---|---|---|---|
| AI assistant built in | Included | Twilio AI / ConversationRelay extra | Vonage AI extra |
| REST + GraphQL | Both | REST | REST |
| Webhook system | 20+ events | Very strong | Strong |
| SDKs | Node, Python, PHP, Go, .NET | All common | All common |
| Free sandbox | Yes | Trial credits | Trial credits |
| Server location | Germany | Global, EU region selectable | Global |
| GDPR without workarounds | Yes | SCC + region pinning | SCC |
| Buy-Phone-Number API | DE/EU | Global | Global |
How developers use the API
Three real configurations.
Invoicing-software provider
Outbound calls via the voiceOne API for dunning processes: zahlungsübersicht.api → the voiceOne API calls the debtor, qualifies willingness to pay, writes the result to the CRM. 70 % automation rate.
Marketing agency Berlin
Own voice bot for a telco customer: the audio stream of the voiceOne calls is forwarded live to their own ML model. Bot responses come back via WebRTC.
Machine builder Schwaben
Call event → ERP lookup via webhook → order status. The AI says on the phone: "Your order 1234 is in production, shipping on 12.06." — data comes from the ERP.
Included in the voiceOne plan
Get in touch with us for a bespoke quote. We configure volume, users and add-ons to suit your sector.
Request a developer sandbox
We set up a sandbox account for you. You get an API key, test number, Postman collection — free and with no obligation.
Frequently asked questions
Sandbox up and running in 5 minutes.
Get an API key, import the Postman collection, start your first call — free.