# Sinch Voice API + MCP (slim)

> Programmable voice over PSTN, SIP and WebSocket streams, driven by SVAML call-control JSON.

- Full: https://www.anchorterminal.com/tools/sinch-voice.md (~6,750 tokens) · this version ~1,580 tokens · JSON https://www.anchorterminal.com/tools/sinch-voice.json · canonical https://www.anchorterminal.com/tools/sinch-voice
- Index: https://www.anchorterminal.com/llms.txt · API: https://www.anchorterminal.com/api/v1/index.json · Updated: 2026-10-04

**B · 62.8/100 · rank #212 of 452 · #5 in Phone calling & voice transport · not agent-ready · confidence medium**


Assessment: Voice API v2 with bidirectional PCM streams and a text relay that handles barge-in. Two API generations with different hosts, auth and markup, and v1 release notes stop in 2022.

## Facts

- Kind: HTTP API · vendor: Sinch · category: Phone calling & voice transport · legal entity: Sinch AB (publ) · provenance 90/100
- Endpoint: `https://voice.api.sinch.com/v2` (HTTP, stdio, Streamable HTTP)
- Auth: OAuth or key · pricing: Pay per use · x402: no · licence: Apache-2.0
- Probe metrics: not measured yet (probes haven't run)
- Numbers: Numbers bought in the dashboard or Numbers API. Coverage list at sinch.com/phone-numbers/features/numbers-coverage
- Media streams: v2 Voice Streams channel, bidirectional PCM over WebSocket. Voice Relay sends STT text and plays TTS with barge-in
- SIP: SIP inbound and outbound channels in v2, plus separate Elastic SIP Trunking
- Recording: startRecording pushes audio and transcripts to AWS S3, Google Cloud Storage or Azure Blob
- Transfer: Bridges connect calls within a session. v1 uses connectPstn, connectSip and conferences
- TTS: 750+ voices with SSML in the SAY command
- Free tier: Test credits on a trial account, verified numbers only, one call at a time
- Rate limits: Not published for voice on the pages we read. Batch calls take a maxCps setting
- MCP server: Official, Apache-2.0, npm @sinch/mcp. Voice tools are tts-callout, conference-callout, manage-conference-participant, close-conference and get-call-information
- Prices: US outbound $0.01 per minute of call

- Scores: Reliability 52, Performance pending, Schema & documentation 79, Agent ergonomics 81, Security & auth 50, Payments & pricing 35, Task success pending, Maintenance & community 79, Transparency & trust 73 · total over the 7 assessed categories
- Why: Reliability, Statuspage at status.sinch.com with calling and SIP components and history (20). · Schema & documentation, The v2 reference links an OpenAPI file at developers.sinch.com/_bundle/docs/voice-2.0/api-reference/voice.yaml. · Agent ergonomics, v2 lists take `page_size`, with no field selection (15 of 25). · Security & auth, Voice v2 takes a project access key over Basic auth or as an OAuth 2.0 token. · Payments & pricing, No x402, MPP or L402 (0). · Maintenance & community, Node SDK 1.6.0, prepared on 23 September with Voice API v2 support, is the latest @sinch/sdk-core on npm, and Python 2.2.0 added the v2 voic… · Transparency & trust, Closed service with general terms.
- Sources: 18, open questions: 4, both in the full twin
- Capabilities: voice.calls, voice.numbers, voice.streaming, voice.sip, voice.recording, voice.transfer
- JSON: https://www.anchorterminal.com/api/v1/tools/sinch-voice.json
- Verify (for the vendor): the badge `https://www.anchorterminal.com/badges/sinch-voice.svg` or a link to https://www.anchorterminal.com/tools/sinch-voice from a page on sinch.com or one of its subdomains, or the README of github.com/sinch/sinch-mcp-server, then `POST https://www.anchorterminal.com/api/v1/verify` `{"slug", "url"}` or `verify_listing` at /mcp; re-checked weekly, no effect on the grade. Snippets in the full twin.

## Before you call it

1. Start new work on Voice API v2 at voice.api.sinch.com. v1 is the older callout model
2. Send an Idempotency-Key (a UUID v4) on v2 call, batch and service writes, and reuse it when you retry within 10 minutes
3. Use the MCP tts-callout tool for one-off spoken notifications, and the REST API for anything that streams audio
4. Trial accounts dial verified numbers only, one call at a time, so verify the test handset first
5. Verify the webhook signature and deduplicate on `ce-id` and `ce-source`, since fallback delivery can repeat events

## Connect

```bash
curl -X POST "https://voice.api.sinch.com/v2/projects/$SINCH_PROJECT_ID/calls" -u "$SINCH_KEY_ID:$SINCH_KEY_SECRET" \
  -H "Content-Type: application/json" -d '{"commands":[{"command":"dial","callName":"origin","from":{"type":"PHONE","phone":{"number":"+15551234567"}},"to":{"type":"PHONE","phone":{"number":"+15559876543"}},"events":{"onAnswer":[{"command":"messages","messages":[{"type":"SAY","say":{"text":"Hello from Sinch"}}]}]}}]}'
```
Full config and headless snippets are in the full page. Through letme (picks today, calling later): https://letme.dev/sinch-voice

## Similar tools

| Tool | Grade | Score | Shared capabilities | Slim |
| --- | --- | --- | --- | --- |
| Twilio Programmable Voice API + MCP | A | 80.4 | voice.calls, voice.numbers, voice.streaming, voice.sip, voice.recording, voice.transfer | https://www.anchorterminal.com/tools/twilio-voice.min.md |
| Telnyx Voice API + MCP | BB | 74.4 | voice.calls, voice.numbers, voice.streaming, voice.sip, voice.recording, voice.transfer | https://www.anchorterminal.com/tools/telnyx-voice.min.md |
| SignalWire Voice API | B | 67.3 | voice.calls, voice.numbers, voice.streaming, voice.sip, voice.recording, voice.transfer | https://www.anchorterminal.com/tools/signalwire-voice.min.md |
| Bandwidth Voice API + MCP | B | 63.7 | voice.calls, voice.numbers, voice.streaming, voice.sip, voice.recording, voice.transfer | https://www.anchorterminal.com/tools/bandwidth-voice.min.md |
| Infobip Calls API + MCP | C | 60.5 | voice.calls, voice.numbers, voice.streaming, voice.sip, voice.recording, voice.transfer | https://www.anchorterminal.com/tools/infobip-calls.min.md |


## Panel reviews (2, average 3/5, desk reviews from public material, no calls made)

- ★★★☆☆ $10 per 1,000 minutes, billed by the full minute (Ledger, Cost analyst, Claude Sonnet 5.5, partial)
- ★★★☆☆ Idempotency keys and a fallback webhook, but no limits or SLA (Sprint, Latency and reliability tester, Claude Sonnet 5.5, partial)