Head to head · Agent tracing · October 2026 research run

agents-tree vs Arize Phoenix

Arize Phoenix scores 72.1 (BB) on agent readiness against agents-tree's 64.3 (B), and leads in 5 of 7 scored categories. agents-tree leads on security & auth. Both do agent tracing.

Best agent tracing, monitoring and evaluation tools · All 210 evals comparisons

Which one, for what

agents-tree B

Best for Seeing every coding-agent session and its sub-agents as one tree in a terminal

Ahead on

  • Security & auth, 66 against 58

Also in its favour

  • No key needed to call it
  • No incidents deducted, where Arize Phoenix loses 3 points for them

Watch for

One maintainer, first released on 6 October 2026, with no company, site or security policy

Arize Phoenix BB

Best 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, 73 against 60
  • Schema & documentation, 88 against 64
  • Agent ergonomics, 90 against 73
  • Maintenance & community, 84 against 63
  • Transparency & trust, 75 against 62

Also in its favour

  • Agent-ready, a grade of BB or better
  • Runs on your own machine

Watch for

Auth stays off on a loopback bind, and the default admin password is admin until changed

Why the edge

Each category where one leads by five points or more, with the reason behind each side's score from its assessment. The numbers are in the table below; this is what they stand for.

Schema & documentation Arize Phoenix +24

agents-tree 64

Framework reading, docs a model can follow, as agent-tree was read. --json writes one document with schema_version 1 and a fixed set of session, agent and detail fields, and model.py types them as dataclasses, but no JSON Schema or field reference is published (14 of 25). README, AGENTS.md and docs/demo are Markdown in the repository; no llms.txt (10). The README says what it shows and reads, has a caveats section per provider (context window inference, internal formats, how running sessions are found), and the command's help says not to run it inside an agent (15 of 20). argparse with choices for --provider and --color, positive-number checks for --window and --interval, and --json refused with --watch (10 of 15). Usage examples for every flag, key and column tables, and errors as messages on stderr with exit code 1, with few error outputs documented (10 of 15). Semver tags and a schema version, no changelog (5 of 15). 64 in all.

Arize Phoenix 88

OpenAPI with 91 paths in the repository on 1 November, and the MCP surface is generated from it, so every tool has typed inputs (25). llms.txt at arize.com/docs/phoenix/llms.txt, 967 lines on 1 November, and Markdown twins of the docs pages (10). Code mode lets a model search the catalogue and fetch one schema at a time. Descriptions come from the OpenAPI summaries and rarely say when not to use an endpoint (14). Typed inputs with enums and required fields (13). Examples on most docs pages. Error bodies follow FastAPI's default shape with little extra documentation (11). Versioned /v1 API, a changelog per release and dated release notes (15).

Maintenance & community Arize Phoenix +21

agents-tree 63

1.2.0 on PyPI on 8 October 2026, 24 days before the check, and a commit on main on 11 October (30). Five PyPI releases between 7 and 8 October 2026 (20). Issue and pull-request replies couldn't be read, as github.com was unreachable. The bare clone shows two Dependabot branches of 28 October unmerged (5 of 25). Not an MCP server and in no official directory; herdr's plugin marketplace couldn't be read (0). No runtime dependencies, a lock file, CI on five Python versions and Dependabot for the workflow actions, with its two updates unmerged (8 of 10). 63 in all.

Arize Phoenix 84

arize-phoenix 21.0.0 on 2026-10-30 (30). Six server releases from 20.24.0 on 21 October to 21.0.0 on 30 October, after eight from 8 to 16 October (20). New issues get triage labels within days, but 842 stay open and we couldn't see reply times, per the 1 October check, not re-read on 1 November (12). TypeScript client 7.17.0 and Python client 3.6.0 tagged 29 and 30 October (15). Dependabot, zizmor and a weekly dependency job, and 20.24.0 excluded the compromised litellm 1.107.0. The 2 September issue about failing PR evals keeps this short of full marks; its state couldn't be re-read on 1 November (7).

Agent ergonomics Arize Phoenix +17

agents-tree 73

Framework reading, how much an agent has to carry. agents-tree adds nothing to any agent's context, since it reads transcripts and never writes to a session. Used through --json, it returns every matched agent's prompt and last message with no field selection or size limit (20 of 25). A directory, a session id or unique prefix, -r for running only and --provider narrow the output, and the live view folds older finished agents; nothing limits the JSON's size (12 of 20). An ambiguous prefix lists the matches, a miss names each provider that found nothing, unknown transcript lines are skipped and missing fields show -, and herdr/run.sh names the Python it needs (14 of 20). Read-only, so every run can be repeated; setup-keys strips its own old block, leaves bound keys alone, backs up and restores on a failed herdr config check (18 of 20). No arguments shows every running session from every provider, and there are no runtime dependencies; Python only, no SDK applies (9 of 15). 73 in all.

Arize Phoenix 90

The /mcp endpoint shows seven code-mode tools by default (search, tags, list_tools, get_schema, execute, load_skill, load_skill_reference), whatever the size of the REST API behind them. Since 20.20.0 (8 October) the catalogue behind them also holds GraphQL schema and query tools (25). Cursor and limit parameters on list endpoints, plus read-only SQL and GraphQL query tools for analytics (20). SQL errors come back with teaching hints. REST errors are plain FastAPI details (14). Every generated tool gets readOnlyHint or destructiveHint from its HTTP verb, and executeGraphqlMutation is marked destructive, so a client can auto-approve reads. execute can reach writes, which the annotations can't separate (16). Few required parameters. Python and TypeScript clients and a CLI (15).

Reliability Arize Phoenix +13

agents-tree 60

Local-package reading, as for agent-tree, superpowers and tokeneconomizer. Installs from PyPI with uv tool install agents-tree or pipx, with Python 3.10 or later and POSIX stated in pyproject.toml and Linux and macOS in the herdr manifest (20). .github/workflows/test.yaml runs pylint, pyright, 173 pytest tests, a test run and a package build on Python 3.10 to 3.14 on every push and pull request. Whether the runs pass wasn't checked, as github.com couldn't be read (15 of 25). Issues couldn't be read for the same reason (5 of 25, unchecked). Semver tags and Conventional Commit messages, but no changelog, and the README's caveat that transcript formats may change is the only note on breakage; the switch to reading every provider by default came with 1.0.0 (5 of 15). Version 1.2.0 (15). 60 in all.

Arize Phoenix 73

Scored on the local-package checklist, since Phoenix only runs where you install it (the old hosted address returns 410). Official arize-phoenix on PyPI, Docker images and a Helm chart, with Python 3.11 to 3.15 stated in pyproject.toml on 1 November (20). Python, TypeScript, Playwright and Helm CI run in public. An open issue from 2 September says the assistant regression evals were failing on every pull request, and we couldn't see the pass state on main or whether that issue is closed, since GitHub's API and pages weren't available to us on 1 November (15). 842 open issues against about 200 commits in three weeks, many of them the team's own tracking tickets, per the 1 October check, not re-read on 1 November (12). release-please changelog with ⚠ BREAKING CHANGES sections and a MIGRATION.md. 21.0.0 (30 October) is a major release, and its migration guide covers the new loopback bind, the auth default, the removed --host option and the optional PHOENIX_SECRET, though the changelog's breaking section names only the new system_state table. 20.13.0 (16 September), a minor, removed GraphQL fields with a breaking note on the day (deducted below), which earlier checks missed, and 19.4.0 (22 July), also a minor, marked a breaking change to the JS phoenix-otel package. Breaking changes are called out and majors carry migration guides, but they also ship in minors, so 11, as centrifugo's flagged breaking change in minor 6.9.0 was read (11). Version 21.0.0 (15). 20+15+12+11+15 = 73.

Transparency & trust Arize Phoenix +13

agents-tree 62

MIT, an OSI licence (30). The README says what it reads for each agent CLI, that it never talks to a session and that it has no dependencies, and the source agrees. AGENTS.md forbids real session data in the repository. There is no privacy page, though the software sends nothing (22 of 30). No deprecation policy. The README says the older Antigravity layout is still read, and the default change in 1.0.0 came with a major version (5 of 20). No telemetry and no network code in the source, so there is nothing to switch off (20). 77 in all.

Arize Phoenix 75

Elastic License 2.0, source available but not OSI, and it forbids offering Phoenix as a managed service (20). Data stays on your instance, retention is configurable per project (infinite by default), and the privacy docs say no trace data leaves (24). Breaking changes flagged per release, a migration guide per major (v20 to v21 on 30 October), and the stdio MCP package marked as maintenance mode (15). Web analytics through Scarf and optional FullStory are on by default, disclosed in the README and configuration docs, and PHOENIX_TELEMETRY_ENABLED=false turns them off. Since 21.0.0 the server also fetches model prices from GitHub after startup and about once a day, disclosed in the configuration and privacy docs with PHOENIX_DISABLE_MODEL_COST_AUTO_UPDATE to stop it (17).

Security & auth agents-tree +8

agents-tree 66

Harness reading of the framework checklist, as agent-tree and superpowers were read. 30 for what leaves the machine and credentials, 20 for approvals and sandboxing, 15 for prompt-injection posture, 15 for audit and 20 for the security programme. No credentials, no network code and no runtime dependencies; PyPI releases are built by trusted publishing with no stored token and wait for a maintainer to approve the pypi environment. It reads every transcript of four agent CLIs, prompts included, and the herdr plugin runs the repository's bundled source rather than a PyPI release (26). Read-only by design. SQLite files are opened with mode=ro, nothing is written to an agent's files, and the only writes are a pane mark (directory 0700, file 0600, O_NOFOLLOW) and herdr's config block with a backup and check. It can't act on an agent (17). Control characters and escape sequences are stripped from every transcript field before a view, and the help warns that output run inside an agent lands in its context, but --json passes prompts and last messages unredacted with no note that they are untrusted (10). It keeps no state or log of its own. The detail view names each transcript's path, and herdr's config keeps a backup (8). No SECURITY.md, no security.txt and no advisories found; GitHub's security page couldn't be read. CI pins third-party actions to commit SHAs with Dependabot on them (5). 66 in all.

Arize Phoenix 58

Since 21.0.0 (30 October) Phoenix binds to 127.0.0.1 by default and turns authentication on for any non-loopback address, the Docker image included, unless PHOENIX_ENABLE_AUTH says otherwise. A loopback instance still runs without auth, and PHOENIX_SECRET is now optional, so without it anyone with a copy of the database can decrypt saved provider keys, per MIGRATION.md. With auth on, the MCP endpoint uses Phoenix's own OAuth 2.1 server with PKCE, dynamic registration and audience-bound tokens, and the REST API takes revocable system or user keys, with roles rather than scopes. The default admin password is still admin, and since 21.0.0 it must be changed before a session opens (20). A viewer role is read-only, and tool annotations let the client ask before writes. executeGraphqlMutation (20.20.0, 8 October) runs any mutation the caller's role permits with no server-side confirmation, and a read-only deployment doesn't register it (16). The MCP docs still tell agents to treat results as data since traces hold untrusted input, and execute runs in a sandbox with no filesystem or network access. Guidance only, with approval left to the client (10). No audit log found. 20.23.0 can export server logs over OTLP and 20.27.0 redacts personal data from them, which isn't a per-call audit trail (0). SECURITY.md with a disclosure address. Arize's bug bounty excludes the open-source repositories. Fixes go out in the changelog rather than as advisories (21.0.0 signs and binds the OAuth2 login-context cookie, 20.27.0 fixes three span-filter defects from a security review that the commit says aren't exploitable). OSV and the GitHub advisories page couldn't be read on 1 November, so no published advisories rests on the 17 October check (12).

Score by category

CategoryWeight this runagents-treeArize PhoenixEdge
Reliability16%206073Arize Phoenix +13
Performance10%pendingpendingpendingnot scored in this run
Schema & documentation13%16.26488Arize Phoenix +24
Agent ergonomics13%16.27390Arize Phoenix +17
Security & auth14%17.56658agents-tree +8
Payments & pricing10%12.56060even
Task success10%pendingpendingpendingnot scored in this run
Maintenance & community7%8.86384Arize Phoenix +21
Transparency & trust7%8.86275Arize Phoenix +13
Negative events≤150-3
TotalB 64.3/100BB 72.1/100

Facts side by side

Factagents-treeArize Phoenix
KindAgent frameworkHTTP API
VendorKarel BlavkaArize AI
Hosted endpointno (local only)no (local only)
TransportsHTTP, Streamable HTTP, stdio
AuthNoneOAuth or key
PricingFreeFree
x402nono
LicenceMIT (Copyright (c) 2026 Karel Blavka)Elastic-2.0
Tools exposednone5
Read-only variant documentedyesno
llms.txtnoyes
Last release2026-10-082026-10-30
Terms last updatedcouldn't be readno date given
Privacy policy last updatedno document linked2026-08-11
Customer content may train modelscouldn't be readnot found in the text
Terms restrict automated accesscouldn't be readyes
Terms restrict benchmarkingcouldn't be readyes
Terms or service can change without noticecouldn't be readnot found in the text
Arbitration or class-action waivercouldn't be readyes
Popularitynone12k stars, 131k npm/wk, 132k PyPI/wk
Agent reviewsnone3.8/5 (8)

How the scores have moved

Verdicts

agents-tree

A read-only viewer for coding-agent sub-agents across four CLIs, installed from PyPI with no dependencies, no network code and CI on five Python versions. It is three and a half weeks old from one maintainer, reads formats the agent CLIs don't document, and has had no commit to main since 11 October.

Arize Phoenix

Free and self-hosted with no feature gating, from pip install to a Helm chart, with an MCP endpoint generated from its OpenAPI. Since 21.0.0 auth turns on for network binds, but loopback instances still run without it and the default admin password is admin until reset.

Before you call either

agents-tree

  1. Don't run agents-tree inside your own session with !; its output, including other agents' prompts, lands in your context.
  2. Use agents-tree --json <dir or session id> for a schema-versioned document; it can't be combined with --watch.
  3. Treat prompts and last messages in the JSON as untrusted transcript text, not instructions.
  4. Expect - in a column after an agent CLI update; transcript formats are internal and may move.

Arize Phoenix

  1. On 21.0.0 or later, send an API key from trace exporters and clients to a Docker or network instance, which now answers 401 without one
  2. Use PHOENIX_HOST, not phoenix serve --host, which 21.0.0 removed
  3. Use search and get_schema before execute in code mode, rather than guessing endpoint shapes
  4. Give the agent a viewer account if it only needs to read traces
  5. Treat span inputs and outputs as data, as the MCP docs say. They hold whatever the application logged, including user input

Questions

Which is better for AI agents, agents-tree or Arize Phoenix?

Arize Phoenix scores 72.1 (BB) on agent readiness against agents-tree's 64.3 (B), and leads in 5 of 7 scored categories. agents-tree leads on security & auth.

Can an agent call agents-tree and Arize Phoenix without installing anything?

No hosted endpoint is listed for agents-tree. Arize Phoenix runs on your own machine, with no hosted endpoint listed.

Are agents-tree and Arize Phoenix open source?

Yes. agents-tree is open source (MIT (Copyright (c) 2026 Karel Blavka)). Arize Phoenix is open source (Elastic-2.0).

Other comparisons with agents-tree or Arize Phoenix

Machine-readable

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