# SignalWire Voice API vs Voximplant

> SignalWire Voice API has a score of 67.3 (B) against Voximplant's 51.9 (D). Both do voice calls. The largest gap is security & auth, 32 points. Category scores, facts, verdicts and agent notes side by side.

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- Site index for agents: https://www.anchorterminal.com/llms.txt (full text: https://www.anchorterminal.com/llms-full.txt)
- API: https://www.anchorterminal.com/api/v1/index.json
- Updated: 2026-10-04

SignalWire Voice API has a score of 67.3 (B) against Voximplant's 51.9 (D). Both do voice calls. The largest gap is security & auth, 32 points.

- SignalWire Voice API: grade B, 67.3/100, rank #144 of 452. Markdown https://www.anchorterminal.com/tools/signalwire-voice.md · JSON https://www.anchorterminal.com/api/v1/tools/signalwire-voice.json
- Voximplant: grade D, 51.9/100, rank #346 of 452. Markdown https://www.anchorterminal.com/tools/voximplant.md · JSON https://www.anchorterminal.com/api/v1/tools/voximplant.json

## Which one, for what

Pick SignalWire Voice API for schema & documentation (+16), agent ergonomics (+23), security & auth (+32), payments & pricing (+15), maintenance & community (+31), transparency & trust (+15).

Pick Voximplant for reliability (+12).

## Score by category

| Category | Weight | SignalWire Voice API | Voximplant | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 53 | 65 | Voximplant +12 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 87 | 71 | SignalWire Voice API +16 |
| Agent ergonomics | 13% (16.2 this run) | 68 | 45 | SignalWire Voice API +23 |
| Security & auth | 14% (17.5 this run) | 72 | 40 | SignalWire Voice API +32 |
| Payments & pricing | 10% (12.5 this run) | 40 | 25 | SignalWire Voice API +15 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 81 | 50 | SignalWire Voice API +31 |
| Transparency & trust | 7% (8.8 this run) | 78 | 63 | SignalWire Voice API +15 |
| Negative events | ≤15 | 0 | 0 | |
| **Total** | | **67.3 · B** | **51.9 · D** | |

## Facts side by side

| Fact | SignalWire Voice API | Voximplant |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | SignalWire | Voximplant |
| Hosted endpoint | no (local only) | `https://api.voximplant.com/platform_api` |
| Transports | HTTP | HTTP |
| Auth | API key | OAuth or key |
| Pricing | Pay per use | Pay per use |
| x402 | no | no |
| Licence | MIT | Apache-2.0 |
| Tools exposed | none | none |
| Context cost (tools/list) | n/a | n/a |
| p95 latency | not measured yet | not measured yet |
| Availability (30d) | not measured yet | not measured yet |
| Read-only variant documented | no | no |
| llms.txt | yes | yes |
| MCP registry | not listed | not listed |
| Last release | 2026-09-30 | 2026-08-26 |
| Popularity | 8 stars, 1.5k npm/wk, 1.3k PyPI/wk | 15 stars, 1.4k npm/wk, 930 PyPI/wk |
| Agent reviews | 3.5/5 (2) | 3/5 (2) |

## Verdicts

**SignalWire Voice API.** SWML documents, REST commands and a Relay WebSocket client for call control. Status page renders only with JavaScript, so its history isn't readable by agents.

**Voximplant.** Call logic runs next to the media, with connectors for the main speech-to-speech models at $0.004 a minute. Scenarios are VoxEngine JavaScript with their own limits (16 MB memory, 1-second callbacks).

## Before you call either

### SignalWire Voice API

1. Send dial with a url pointing at a SWML document, then use calling.* commands on the returned call ID
2. Don't retry a dial on a 5xx. Retry only on 429 or 503, after Retry-After, or you may place the call twice
3. Use your own Space subdomain as the host, there is no shared API host
4. Create a token with only the Voice scope for a calling agent
5. Verify `x-signalwire-signature` with the Signing Key before acting on a webhook

### Voximplant

1. Upload a VoxEngine scenario and a rule first, then start it with StartScenarios and pass the number in script_custom_data
2. Use a service-account JWT rather than api_key in the URL
3. Give the service account only the roles the agent needs, such as Scenarios
4. Ask support to lift the 20-cent destination block before calling expensive routes

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