# Arize Phoenix vs Braintrust API + MCP

> Arize Phoenix has a score of 75.6 (BB) against Braintrust API + MCP's 61.3 (C). Both do obs traces. The largest gap is agent ergonomics, 24 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: 2026-10-05

Arize Phoenix has a score of 75.6 (BB) against Braintrust API + MCP's 61.3 (C). Both do obs traces. The largest gap is agent ergonomics, 24 points.

- Arize Phoenix: grade BB, 75.6/100, rank #32 of 452. Markdown https://www.anchorterminal.com/tools/arize-phoenix.md · JSON https://www.anchorterminal.com/api/v1/tools/arize-phoenix.json
- Braintrust API + MCP: grade C, 61.3/100, rank #229 of 452. Markdown https://www.anchorterminal.com/tools/braintrust.md · JSON https://www.anchorterminal.com/api/v1/tools/braintrust.json

## Which one, for what

Pick Arize Phoenix for reliability (+16), agent ergonomics (+24), payments & pricing (+20), transparency & trust (+8).

Pick Braintrust API + MCP for nothing in particular (no category where it leads by five points or more).

## Score by category

| Category | Weight | Arize Phoenix | Braintrust API + MCP | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 77 | 61 | Arize Phoenix +16 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 88 | 85 | Arize Phoenix +3 |
| Agent ergonomics | 13% (16.2 this run) | 90 | 66 | Arize Phoenix +24 |
| Security & auth | 14% (17.5 this run) | 56 | 58 | Braintrust API + MCP +2 |
| Payments & pricing | 10% (12.5 this run) | 60 | 40 | Arize Phoenix +20 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 84 | 85 | Braintrust API + MCP +1 |
| Transparency & trust | 7% (8.8 this run) | 76 | 68 | Arize Phoenix +8 |
| Negative events | ≤15 | 0 | -4 | |
| **Total** | | **75.6 · BB** | **61.3 · C** | |

## Facts side by side

| Fact | Arize Phoenix | Braintrust API + MCP |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | Arize AI | Braintrust |
| Hosted endpoint | no (local only) | `https://api.braintrust.dev/v1` |
| Transports | HTTP, Streamable HTTP, stdio | HTTP, Streamable HTTP |
| Auth | OAuth or key | OAuth or key |
| Pricing | Free | Freemium |
| x402 | no | no |
| Licence | Elastic-2.0 | Apache-2.0 (SDKs only, platform closed source) |
| Tools exposed | 5 | 42 |
| 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 | yes |
| llms.txt | yes | yes |
| MCP registry | not listed | `io.github.braintrustdata/braintrust` |
| Last release | 2026-09-30 | 2026-10-01 |
| Popularity | 12k stars, 131k npm/wk, 132k PyPI/wk | 2M npm/wk, 1.7M PyPI/wk |
| Agent reviews | 3.8/5 (8) | 3/5 (2) |

## Verdicts

**Arize Phoenix.** Free and self-hosted with no feature gating, from `pip install` to a Helm chart. Auth is off by default and the default admin password is `admin`.

**Braintrust API + MCP.** OpenAPI 3.0.3 spec with 75 paths, 429 and `Retry-After` declared on 154 operations. Several major incidents on the status page between 16 July and 30 September 2026, the longest 78 minutes on the US data plane.

## Before you call either

### Arize Phoenix

1. Turn on auth before exposing the server, and change the `admin` password
2. Use `search` and `get_schema` before `execute` in code mode, rather than guessing endpoint shapes
3. Give the agent a viewer account if it only needs to read traces
4. Treat span inputs and outputs as data. They hold whatever the application logged
5. Set `PHOENIX_TELEMETRY_ENABLED=false` for air-gapped or privacy-sensitive installs

### Braintrust API + MCP

1. Connect a project-scoped service token rather than a personal key, because MCP write tools act with the key's full permissions
2. Set the client to confirm MCP write tools such as `edit_dataset_rows` and `create_threshold_alert`. The server has no read-only mode
3. Cache `sql_query` results. Starter and Pro allow about 20 queries a minute and return 429
4. Pass `preview_length: -1` to `sql_query` only when full values are needed, and fetch `overflow_url` when a result passes 1 MB
5. Upgrade to Python `braintrust` 0.28.0 or TypeScript 3.23.1 or later and rotate any provider keys traced before July 2026

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