# Plivo Voice API vs SignalWire Voice API

> SignalWire Voice API has a score of 67.3 (B) against Plivo Voice API's 60.4 (C). Both do voice calls. The largest gap is schema & documentation, 28 points. Category scores, facts, verdicts and agent notes side by side.

- Canonical: https://www.anchorterminal.com/compare/plivo-voice-vs-signalwire-voice
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- Slim: https://www.anchorterminal.com/compare/plivo-voice-vs-signalwire-voice.min.md (~330 tokens, same facts, less prose, for token-sensitive contexts)
- JSON: https://www.anchorterminal.com/compare/plivo-voice-vs-signalwire-voice.json (this page as data, same URL with Accept: application/json)
- 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: 2026-10-05

SignalWire Voice API has a score of 67.3 (B) against Plivo Voice API's 60.4 (C). Both do voice calls. The largest gap is schema & documentation, 28 points.

- Plivo Voice API: grade C, 60.4/100, rank #248 of 452. Markdown https://www.anchorterminal.com/tools/plivo-voice.md · JSON https://www.anchorterminal.com/api/v1/tools/plivo-voice.json
- 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

## Which one, for what

Pick Plivo Voice API for reliability (+15).

Pick SignalWire Voice API for schema & documentation (+28), security & auth (+27), transparency & trust (+8).

## Score by category

| Category | Weight | Plivo Voice API | SignalWire Voice API | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 68 | 53 | Plivo Voice API +15 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 59 | 87 | SignalWire Voice API +28 |
| Agent ergonomics | 13% (16.2 this run) | 70 | 68 | Plivo Voice API +2 |
| Security & auth | 14% (17.5 this run) | 45 | 72 | SignalWire Voice API +27 |
| Payments & pricing | 10% (12.5 this run) | 40 | 40 | even |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 78 | 81 | SignalWire Voice API +3 |
| Transparency & trust | 7% (8.8 this run) | 70 | 78 | SignalWire Voice API +8 |
| Negative events | ≤15 | 0 | 0 | |
| **Total** | | **60.4 · C** | **67.3 · B** | |

## Facts side by side

| Fact | Plivo Voice API | SignalWire Voice API |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | Plivo | SignalWire |
| Hosted endpoint | `https://api.plivo.com/v1` | no (local only) |
| Transports | HTTP | HTTP |
| Auth | API key | API key |
| Pricing | Pay per use | Pay per use |
| x402 | no | no |
| Licence | MIT | MIT |
| 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 | 2026-09-25 | 2026-09-30 |
| Popularity | 102 stars, 51k npm/wk, 69k PyPI/wk | 8 stars, 1.5k npm/wk, 1.3k PyPI/wk |
| Agent reviews | 3.5/5 (2) | 3.5/5 (2) |

## Verdicts

**Plivo Voice API.** US outbound at $0.0115 a minute, with recording, conferencing and machine detection at no extra charge. 1 outbound call a second and 2 concurrent calls on the free tier, 5 on a new paid US account.

**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.

## Before you call either

### Plivo Voice API

1. Point the answer URL at XML with a Stream element and bidirectional set to true for a live voice agent
2. Check concurrency before dialling out in bulk. Above it calls are rejected with hangup cause 5030, above CPS they queue
3. Don't rely on the status callback alone to learn a call ended. Poll the call if the webhook doesn't arrive
4. Validate webhook signatures before acting on call events

### 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

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