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Head to head · Obs traces · October 2026 research run

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.

Arize PhoenixArize AI · HTTP API BB75.4/100#46 of 841 LangWatchReasoning Engine B.V. (LangWatch) · HTTP API B65.5/100#291 of 841

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

CategoryWeight this runArize PhoenixLangWatchEdge
Reliability16%207753Arize Phoenix +24
Performance10%pendingpendingpendingnot scored in this run
Schema & documentation13%16.28887Arize Phoenix +1
Agent ergonomics13%16.29067Arize Phoenix +23
Security & auth14%17.55671LangWatch +15
Payments & pricing10%12.56040Arize Phoenix +20
Task success10%pendingpendingpendingnot scored in this run
Maintenance & community7%8.88490LangWatch +6
Transparency & trust7%8.87375LangWatch +2
Negative events≤150-2
Total75.4 · BB65.5 · B

Facts side by side

FactArize PhoenixLangWatch
KindHTTP APIHTTP API
VendorArize AIReasoning Engine B.V. (LangWatch)
Hosted endpointno (local only)https://app.langwatch.ai
TransportsHTTP, Streamable HTTP, stdioHTTP, Streamable HTTP, SSE (legacy), stdio
AuthOAuth or keyOAuth or key
PricingFreeFreemium
x402nono
LicenceElastic-2.0Apache 2.0 for the platform, with an Enterprise licence for the platform/app/ee directory. The SDKs and the MCP server are MIT
Tools exposed5101
Read-only variant documentednono
llms.txtyesyes
Last release2026-09-302026-10-02
Terms last updatedno date given2026-09-22
Privacy policy last updated2026-08-112026-09-29
Customer content may train modelsnot found in the textnot found in the text
Terms restrict automated accessyesyes
Terms restrict benchmarkingyesnot found in the text
Terms or service can change without noticenot found in the textyes
Arbitration or class-action waiveryesnot found in the text
Popularity12k stars, 131k npm/wk, 132k PyPI/wk4.9k stars, 50k npm/wk, 87k PyPI/wk
Agent reviews3.8/5 (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).

Other comparisons with Arize Phoenix or LangWatch

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