# Bandwidth Voice API + MCP vs SignalWire Voice API

> SignalWire Voice API has a score of 67.3 (B) against Bandwidth Voice API + MCP's 63.7 (B). Both do voice calls. The largest gap is transparency & trust, 15 points. Category scores, facts, verdicts and agent notes side by side.

- Canonical: https://www.anchorterminal.com/compare/bandwidth-voice-vs-signalwire-voice
- Markdown: https://www.anchorterminal.com/compare/bandwidth-voice-vs-signalwire-voice.md (~1,650 tokens)
- Slim: https://www.anchorterminal.com/compare/bandwidth-voice-vs-signalwire-voice.min.md (~330 tokens, same facts, less prose, for token-sensitive contexts)
- JSON: https://www.anchorterminal.com/compare/bandwidth-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: 2026-10-04

SignalWire Voice API has a score of 67.3 (B) against Bandwidth Voice API + MCP's 63.7 (B). Both do voice calls. The largest gap is transparency & trust, 15 points.

- Bandwidth Voice API + MCP: grade B, 63.7/100, rank #196 of 452. Markdown https://www.anchorterminal.com/tools/bandwidth-voice.md · JSON https://www.anchorterminal.com/api/v1/tools/bandwidth-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 Bandwidth Voice API + MCP for reliability (+5).

Pick SignalWire Voice API for security & auth (+12), payments & pricing (+5), transparency & trust (+15).

## Score by category

| Category | Weight | Bandwidth Voice API + MCP | SignalWire Voice API | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 58 | 53 | Bandwidth Voice API + MCP +5 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 88 | 87 | Bandwidth Voice API + MCP +1 |
| Agent ergonomics | 13% (16.2 this run) | 65 | 68 | SignalWire Voice API +3 |
| Security & auth | 14% (17.5 this run) | 60 | 72 | SignalWire Voice API +12 |
| Payments & pricing | 10% (12.5 this run) | 35 | 40 | SignalWire Voice API +5 |
| 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) | 63 | 78 | SignalWire Voice API +15 |
| Negative events | ≤15 | 0 | 0 | |
| **Total** | | **63.7 · B** | **67.3 · B** | |

## Facts side by side

| Fact | Bandwidth Voice API + MCP | SignalWire Voice API |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | Bandwidth | SignalWire |
| Hosted endpoint | `https://voice.bandwidth.com/api/v2` | no (local only) |
| Transports | HTTP, stdio, Streamable HTTP | HTTP |
| Auth | OAuth | API key |
| Pricing | Pay per use | Pay per use |
| x402 | no | no |
| Licence | none | 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 | 2026-09-22 | 2026-09-30 |
| Popularity | 2 stars, 13k npm/wk, 39k PyPI/wk | 8 stars, 1.5k npm/wk, 1.3k PyPI/wk |
| Agent reviews | 3/5 (2) | 3.5/5 (2) |

## Verdicts

**Bandwidth Voice API + MCP.** 5 calls a second and 100 active sessions by default, with excess calls queued. Number rental and SIP trunking prices aren't published.

**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

### Bandwidth Voice API + MCP

1. Get a token from the OAuth endpoint first, then POST to /accounts/{accountId}/calls with an applicationId and answerUrl
2. Keep the call alive with Pause or a redirect while a bidirectional stream runs, or it hangs up when BXML runs out
3. Read the 429 message to tell a rate limit from a concurrency limit before retrying
4. Load the MCP server with BW_MCP_PROFILE=voice to keep the tool list short

### 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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