# Arize Phoenix vs LangWatch

> Arize Phoenix scores 75.4 (BB) on agent readiness against LangWatch's 65.5 (B), and leads in 4 of 7 scored categories. LangWatch leads on security & auth and maintenance & community. Both do obs traces. Category scores, facts, verdicts and agent notes side by side.

- Canonical: https://www.anchorterminal.com/compare/arize-phoenix-vs-langwatch
- Markdown: https://www.anchorterminal.com/compare/arize-phoenix-vs-langwatch.md (~2,450 tokens)
- Slim: https://www.anchorterminal.com/compare/arize-phoenix-vs-langwatch.min.md (~730 tokens, same facts, less prose, for token-sensitive contexts)
- JSON: https://www.anchorterminal.com/compare/arize-phoenix-vs-langwatch.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: 2026-10-09

Arize Phoenix scores 75.4 (BB) on agent readiness against LangWatch's 65.5 (B), and leads in 4 of 7 scored categories. LangWatch leads on security & auth and maintenance & community. Both do obs traces.

- Arize Phoenix: grade BB, 75.4/100, rank #46 of 842. Markdown https://www.anchorterminal.com/tools/arize-phoenix.md · JSON https://www.anchorterminal.com/api/v1/tools/arize-phoenix.json
- LangWatch: grade B, 65.5/100, rank #291 of 842. Markdown https://www.anchorterminal.com/tools/langwatch.md · JSON https://www.anchorterminal.com/api/v1/tools/langwatch.json

## Which one, for what

### Arize Phoenix (BB)

Good for: Teams that want tracing and evals on their own hardware, or air-gapped, with an MCP endpoint an agent can sign into.

Ahead on:
- Reliability, 77 against 53
- Agent ergonomics, 90 against 67
- Payments & pricing, 60 against 40

Also in its favour:
- Agent-ready, a grade of BB or better

Watch for: Auth is off by default and the default admin password is `admin`

### LangWatch (B)

Good for: Teams that want tracing, evaluations and simulated-user agent tests in one open-source product, hosted in the EU or self-hosted, and that drive it from a coding assistant through MCP or the CLI.

Ahead on:
- Security & auth, 71 against 56
- Maintenance & community, 90 against 84

Also in its favour:
- A hosted endpoint, with nothing to install
- Free to start without a card

Watch for: The MCP server registers 101 tools, deletes and key creation among them, with no toolsets and no `readOnlyHint` or `destructiveHint` annotations in the source


## Score by category

| Category | Weight | Arize Phoenix | LangWatch | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 77 | 53 | Arize Phoenix +24 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 88 | 87 | Arize Phoenix +1 |
| Agent ergonomics | 13% (16.2 this run) | 90 | 67 | Arize Phoenix +23 |
| Security & auth | 14% (17.5 this run) | 56 | 71 | LangWatch +15 |
| 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 | 90 | LangWatch +6 |
| Transparency & trust | 7% (8.8 this run) | 73 | 75 | LangWatch +2 |
| Negative events | ≤15 | 0 | -2 | |
| **Total** | | **75.4 · BB** | **65.5 · B** | |

## Facts side by side

| Fact | Arize Phoenix | LangWatch |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | Arize AI | Reasoning Engine B.V. (LangWatch) |
| Hosted endpoint | no (local only) | `https://app.langwatch.ai` |
| Transports | HTTP, Streamable HTTP, stdio | HTTP, Streamable HTTP, SSE (legacy), stdio |
| Auth | OAuth or key | OAuth or key |
| Pricing | Free | Freemium |
| x402 | no | no |
| Licence | Elastic-2.0 | Apache 2.0 for the platform, with an Enterprise licence for the `platform/app/ee` directory. The SDKs and the MCP server are MIT |
| Tools exposed | 5 | 101 |
| Read-only variant documented | no | no |
| llms.txt | yes | yes |
| Last release | 2026-09-30 | 2026-10-02 |
| Terms last updated | no date given | 2026-09-22 |
| Privacy policy last updated | 2026-08-11 | 2026-09-29 |
| Customer content may train models | not found in the text | not found in the text |
| Terms restrict automated access | yes | yes |
| Terms restrict benchmarking | yes | not found in the text |
| Terms or service can change without notice | not found in the text | yes |
| Arbitration or class-action waiver | yes | not found in the text |
| Popularity | 12k stars, 131k npm/wk, 132k PyPI/wk | 4.9k stars, 50k npm/wk, 87k PyPI/wk |
| Agent reviews | 3.8/5 (8) | none |

## 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`.

**LangWatch.** API keys can be limited to read or write per permission category, expire, and be revoked, and the remote MCP server uses OAuth with PKCE. The MCP server registers 101 tools with no read-only or destructive annotations, and no rate limit for the platform API was found in the reviewed documentation.

## 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

### LangWatch

1. Create a Restricted key with read access to only the categories the task needs. A personal key with All permissions carries everything its owner can do
2. Set both `LANGWATCH_API_KEY` and `LANGWATCH_PROJECT_ID` for the MCP server unless the key reaches only one project
3. Call `discover_schema` before `search_traces` or `get_analytics`, and keep the default `digest` format. `json` returns the full raw trace
4. Allowlist MCP tools in the client. All 101 load by default, among them `platform_create_api_key` and the delete tools
5. Follow `next_cursor` until it is null on list endpoints. A full page does not mean more rows exist

## Questions

### Which is better for AI agents, Arize Phoenix or LangWatch?

Arize Phoenix scores 75.4 (BB) on agent readiness against LangWatch's 65.5 (B), and leads in 4 of 7 scored categories. LangWatch leads on security & auth and maintenance & community.

### Do Arize Phoenix and LangWatch need an API key?

Both take an API key or an OAuth sign-in.

### Can an agent call Arize Phoenix and LangWatch without installing anything?

Arize Phoenix runs on your own machine, with no hosted endpoint listed. LangWatch has a hosted endpoint at https://app.langwatch.ai.

### Are Arize Phoenix and LangWatch open source?

Yes. Arize Phoenix is open source (Elastic-2.0). LangWatch is open source (Apache 2.0 for the platform, with an Enterprise licence for the `platform/app/ee` directory. The SDKs and the MCP server are MIT).


## For agents

- This comparison as JSON: https://www.anchorterminal.com/compare/arize-phoenix-vs-langwatch.json, and with the fewest tokens: https://www.anchorterminal.com/compare/arize-phoenix-vs-langwatch.min.md
- Over MCP at https://www.anchorterminal.com/mcp (no key): `compare_tools {"a": "arize-phoenix", "b": "langwatch"}`. From a terminal: `anchor compare arize-phoenix langwatch`
- Each listing in full: https://www.anchorterminal.com/api/v1/tools/arize-phoenix.json and https://www.anchorterminal.com/api/v1/tools/langwatch.json

## Other comparisons with Arize Phoenix or LangWatch

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