# SignalWire Voice API vs Telnyx Voice API + MCP

> Telnyx Voice API + MCP has a score of 74.4 (BB) against SignalWire Voice API's 67.3 (B). Both do voice calls. The largest gap is security & auth, 27 points. Category scores, facts, verdicts and agent notes side by side.

- Canonical: https://www.anchorterminal.com/compare/signalwire-voice-vs-telnyx-voice
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- Slim: https://www.anchorterminal.com/compare/signalwire-voice-vs-telnyx-voice.min.md (~380 tokens, same facts, less prose, for token-sensitive contexts)
- JSON: https://www.anchorterminal.com/compare/signalwire-voice-vs-telnyx-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: 2026-10-04

Telnyx Voice API + MCP has a score of 74.4 (BB) against SignalWire Voice API's 67.3 (B). Both do voice calls. The largest gap is security & auth, 27 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
- Telnyx Voice API + MCP: grade BB, 74.4/100, rank #48 of 452. Markdown https://www.anchorterminal.com/tools/telnyx-voice.md · JSON https://www.anchorterminal.com/api/v1/tools/telnyx-voice.json

## Which one, for what

Pick SignalWire Voice API for security & auth (+27), transparency & trust (+5).

Pick Telnyx Voice API + MCP for reliability (+22), schema & documentation (+6), agent ergonomics (+22), payments & pricing (+25).

## Score by category

| Category | Weight | SignalWire Voice API | Telnyx Voice API + MCP | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 53 | 75 | Telnyx Voice API + MCP +22 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 87 | 93 | Telnyx Voice API + MCP +6 |
| Agent ergonomics | 13% (16.2 this run) | 68 | 90 | Telnyx Voice API + MCP +22 |
| Security & auth | 14% (17.5 this run) | 72 | 45 | SignalWire Voice API +27 |
| Payments & pricing | 10% (12.5 this run) | 40 | 65 | Telnyx Voice API + MCP +25 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 81 | 83 | Telnyx Voice API + MCP +2 |
| Transparency & trust | 7% (8.8 this run) | 78 | 73 | SignalWire Voice API +5 |
| Negative events | ≤15 | 0 | 0 | |
| **Total** | | **67.3 · B** | **74.4 · BB** | |

## Facts side by side

| Fact | SignalWire Voice API | Telnyx Voice API + MCP |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | SignalWire | Telnyx |
| Hosted endpoint | no (local only) | `https://api.telnyx.com/v2` |
| Transports | HTTP | HTTP, Streamable HTTP, stdio |
| Auth | API key | OAuth or key |
| Pricing | Pay per use | Pay per use |
| x402 | no | payer tooling only |
| Licence | MIT | MIT |
| Tools exposed | none | 3 |
| 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 | `io.github.team-telnyx/telnyx` |
| Last release | 2026-09-30 | 2026-09-25 |
| Popularity | 8 stars, 1.5k npm/wk, 1.3k PyPI/wk | 197 stars, 417k npm/wk, 179k PyPI/wk |
| Agent reviews | 3.5/5 (2) | 3.5/5 (8) |

## 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.

**Telnyx Voice API + MCP.** About $0.007 a minute all-in for US outbound ($0.002 Voice API plus $0.005 termination). x402 and MPP only top up credit, they don't pay per call.

## 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

### Telnyx Voice API + MCP

1. Create a Call Control application first. `POST /v2/calls` needs its `connection_id`
2. Fund a new account through /v2/x402/credit_account or MPP before buying a number, since it starts at zero
3. Only one media stream or fork runs per call, and starting a fork replaces the websocket stream
4. Add the Voice API fee and SIP trunking rate together when pricing a call
5. Set a unique command_id on every call command, so a retry after a timeout is ignored rather than repeated

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