API · Webhooks · Developer Platform

voiceOne API — open, documented, ready.

REST + GraphQL API. Webhooks for call, booking and CRM events. SDKs for Node.js, Python, PHP, Go. Developer portal with sandbox, OpenAPI spec and Postman collection. Included in your voiceOne plan — also in the 14-day trial.

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REST + GraphQL Sandbox free 5 official SDKs OpenAPI 3.1 spec

Why an open voiceOne API?

Because your stack doesn’t end where voiceOne begins. And because vendor lock-in is an anti-feature.

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REST + GraphQL

Classic REST for standard integrations. GraphQL for complex queries with field selection. Same auth on both.

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Webhooks for events

Call start, call end, booking made, lead captured, CRM update, sentiment trigger. We POST, you process. Retries with exponential backoff.

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Official SDKs

Node.js, Python, PHP, Go, .NET (beta). Fully type-safe, with test coverage, published on npm/PyPI/Composer/Go-Mod.

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Free sandbox

Build against the sandbox endpoint before going live. Test phone numbers, test webhooks, all endpoints — without spending a cent.

API capabilities

Fully modular: take what you need, no forced bundle.

Call API

Initiate, read, modify calls

Start outbound, read live status, receive audio stream live, end call, retrieve recording.

  • WebRTC audio
  • Outbound with caller-ID select
  • Live transcript stream
Webhook system

Push not pull

20+ event types subscribable per URL. Per-tenant filters. 5x retries with backoff. HMAC-SHA256 signature verification.

  • Selective event subscription
  • Custom headers
  • Webhook audit log
CRM API

Contacts, pipelines, tasks

CRUD on contacts, companies, deals, tasks. Bulk ops up to 5,000 items. Custom fields typed correctly.

  • JSON-Schema validated
  • Cursor pagination
  • Soft delete + audit log
Booking API

Programmatic appointments

Check availability, reserve slots, confirm bookings, trigger reminders. Multi-calendar per account.

  • Time-zone aware (IANA)
  • ICS output
  • Conflict detection
Webhook builder

No-code config

In the voiceOne portal: pick event, enter URL, set filters, live test. No code, no effort.

  • DSL filters ("if industry=clinic")
  • Header & body transform
  • Replay for testing
Audio streaming

WebRTC live stream

Receive/send live audio of a call. For custom voice bots, quality monitoring, real-time coaching.

  • Opus & PCM
  • Bi-directional
  • VoIP codec converted

voiceOne API vs. Twilio vs. Vonage

Honest comparison. Twilio is the gold standard for phone APIs. voiceOne plays in a different league: AI assistant + API.

Feature voiceOne Twilio Voice + AI Vonage Voice + AI
Entry price£29/mo (in plan)$0.013/min + add-ons$0.014/min + add-ons
AI assistant built-inInc.Twilio AI extraVonage AI extra
REST + GraphQLBothRESTREST
Webhook system20+ eventsVery strongStrong
SDKsNode, Python, PHP, Go, .NETAll majorAll major
Free sandboxYesTrial creditsTrial credits
Server locationUK/GermanyGlobal, EU optionalGlobal
UK GDPR readyYesSCCs + region pinningSCCs
Pricing modelFlat (£29 in plan)Pay-as-you-goPay-as-you-go
Phone number APIUK/EUGlobalGlobal

As of 05/2026 — all prices per the providers’ public pricing pages. We refresh this table quarterly.

How developers use the API

Three real configurations.

ISV · B2B SaaS

Invoicing software vendor

Outbound calls via voiceOne API for collections: payment-overview API → voiceOne API calls debtor, qualifies willingness to pay, writes result to CRM. 70 % automation rate.

Agency · custom voice bot

Marketing agency London

Custom voice bot for a telco client: voiceOne call audio stream forwarded live to their own ML model. Bot responses back via WebRTC.

Integration · ERP linking

Engineering Birmingham

Call event → ERP lookup via webhook → order status. AI says on the phone: ‘Your order 1234 is in production, dispatch on 12/06.’ — data from ERP.

API in your plan

£29/month
10,000 API requests/day in plan. Sandbox free forever.
REST + GraphQL inc. 5 SDKs inc. Webhook system inc. Sandbox free
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Request a developer sandbox

We set up a sandbox account for you. You get API key, test number, Postman collection — free, no obligation.

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Frequently asked questions

Which auth method does the API use?

Bearer tokens (long-lived) for server-to-server, OAuth 2.0 Authorization Code Flow for user apps. Both over HTTPS only, TLS 1.3. API keys can be restricted by IP whitelist.

What’s the difference between REST and GraphQL?

REST: classic endpoints (GET /contacts, POST /calls). Simpler, works with Postman, good for standard integrations. GraphQL: one endpoint, you pick exactly the fields — leaner for mobile apps.

What are the rate limits?

10,000 requests/day in the standard plan. 60 requests/second burst. Burst increase on request. GraphQL: complexity limit 1,000 per query.

How do webhooks handle network errors?

5 retries with exponential backoff (1s, 5s, 25s, 2min, 10min). Signed body with HMAC-SHA256. On persistent failure: webhook auto-disabled with email.

Is there a sandbox?

Yes, free forever. Test phone numbers, test CRM data, test webhooks. Separate sandbox API key. No real calls, zero cost.

What if I need more volume?

Custom packs from 25,000 requests/day at £45/month extra. Enterprise packs from 1M requests/day with SLA and dedicated solutions engineer.

API versioning policy?

Semantic versioning. Breaking changes only in major versions (v1 → v2) with 12 months deprecation notice. v1 stable since 2024.

Sandbox in 5 minutes.

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