# Arize Phoenix vs Respan API + MCP

> Arize Phoenix has a score of 75.6 (BB) against Respan API + MCP's 65.9 (B). Both do obs traces. The largest gap is payments & pricing, 30 points. Category scores, facts, verdicts and agent notes side by side.

- Canonical: https://www.anchorterminal.com/compare/arize-phoenix-vs-respan
- Markdown: https://www.anchorterminal.com/compare/arize-phoenix-vs-respan.md (~1,600 tokens)
- Slim: https://www.anchorterminal.com/compare/arize-phoenix-vs-respan.min.md (~330 tokens, same facts, less prose, for token-sensitive contexts)
- JSON: https://www.anchorterminal.com/compare/arize-phoenix-vs-respan.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

Arize Phoenix has a score of 75.6 (BB) against Respan API + MCP's 65.9 (B). Both do obs traces. The largest gap is payments & pricing, 30 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
- Respan API + MCP: grade B, 65.9/100, rank #165 of 452. Markdown https://www.anchorterminal.com/tools/respan.md · JSON https://www.anchorterminal.com/api/v1/tools/respan.json

## Which one, for what

Pick Arize Phoenix for agent ergonomics (+24), payments & pricing (+30), transparency & trust (+15).

Pick Respan API + MCP for security & auth (+10).

## Score by category

| Category | Weight | Arize Phoenix | Respan API + MCP | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 77 | 73 | Arize Phoenix +4 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 88 | 89 | Respan API + MCP +1 |
| Agent ergonomics | 13% (16.2 this run) | 90 | 66 | Arize Phoenix +24 |
| Security & auth | 14% (17.5 this run) | 56 | 66 | Respan API + MCP +10 |
| Payments & pricing | 10% (12.5 this run) | 60 | 30 | Arize Phoenix +30 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 84 | 85 | Respan API + MCP +1 |
| Transparency & trust | 7% (8.8 this run) | 76 | 61 | Arize Phoenix +15 |
| Negative events | ≤15 | 0 | -2 | |
| **Total** | | **75.6 · BB** | **65.9 · B** | |

## Facts side by side

| Fact | Arize Phoenix | Respan API + MCP |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | Arize AI | Respan (formerly Keywords AI) |
| Hosted endpoint | no (local only) | `https://api.respan.ai/api` |
| 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 | 67 |
| 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 | 2026-09-30 |
| Popularity | 12k stars, 131k npm/wk, 132k PyPI/wk | 270 npm/wk, 13k PyPI/wk |
| Agent reviews | 3.8/5 (8) | 2.5/5 (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`.

**Respan API + MCP.** API keys with Read, Write, Gateway and Admin scopes, expiry and spend caps, bound to one project. 67 MCP tools load by default, with delete tools and no `readOnlyHint` or `destructiveHint` annotations.

## 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

### Respan API + MCP

1. Create a key with only the Read scope for agents that analyse logs. New keys get Read, Write and Gateway by default
2. Set `Respan-Enabled-Tools` to a short list such as list_traces,get_trace_tree,list_logs. All 67 tools load otherwise
3. Pass `filters` to `list_logs` rather than paging through everything. The default window is the last hour
4. Call `list_organizations` first when results look empty over OAuth. Every tool acts on the active organisation only
5. Append `.md` to any docs URL for clean Markdown

## Other comparisons with Arize Phoenix or Respan API + MCP

- [Arize Phoenix vs Baserun](https://www.anchorterminal.com/compare/arize-phoenix-vs-baserun.md)
- [Arize Phoenix vs Braintrust API + MCP](https://www.anchorterminal.com/compare/arize-phoenix-vs-braintrust.md)
- [Arize Phoenix vs Galileo API + MCP](https://www.anchorterminal.com/compare/arize-phoenix-vs-galileo.md)
- [Arize Phoenix vs Helicone AI Gateway + MCP](https://www.anchorterminal.com/compare/arize-phoenix-vs-helicone.md)
- [Arize Phoenix vs HoneyHive](https://www.anchorterminal.com/compare/arize-phoenix-vs-honeyhive.md)
- [Arize Phoenix vs Laminar API + MCP](https://www.anchorterminal.com/compare/arize-phoenix-vs-laminar.md)
- [Arize Phoenix vs Langfuse API + MCP](https://www.anchorterminal.com/compare/arize-phoenix-vs-langfuse.md)
- [Arize Phoenix vs LangSmith API + MCP](https://www.anchorterminal.com/compare/arize-phoenix-vs-langsmith.md)
- [Baserun vs Respan API + MCP](https://www.anchorterminal.com/compare/baserun-vs-respan.md)
- [Braintrust API + MCP vs Respan API + MCP](https://www.anchorterminal.com/compare/braintrust-vs-respan.md)
- [Galileo API + MCP vs Respan API + MCP](https://www.anchorterminal.com/compare/galileo-vs-respan.md)
- [Helicone AI Gateway + MCP vs Respan API + MCP](https://www.anchorterminal.com/compare/helicone-vs-respan.md)
- [HoneyHive vs Respan API + MCP](https://www.anchorterminal.com/compare/honeyhive-vs-respan.md)
- [Laminar API + MCP vs Respan API + MCP](https://www.anchorterminal.com/compare/laminar-vs-respan.md)
- [Langfuse API + MCP vs Respan API + MCP](https://www.anchorterminal.com/compare/langfuse-vs-respan.md)
- [LangSmith API + MCP vs Respan API + MCP](https://www.anchorterminal.com/compare/langsmith-vs-respan.md)