← Vetro Attest · Free Art. 12/14 checker · Free EU AI Act tools

Vetro Attest vs. Arize Phoenix

*Engineering comparison, not legal advice. Phoenix features change quickly; check their documentation for the current state.*

Phoenix and Vetro Attest do different jobs. Phoenix helps you see and improve what your LLM application does. Vetro Attest turns a trace you already have into evidence that someone outside your company can check.

What Phoenix does well

Phoenix is an open-source observability and evaluation tool built around OpenTelemetry-based tracing. Teams use it to:

• Trace LLM calls, retrieval steps and agent runs, with latency and token usage;
• Evaluate outputs with LLM-as-a-judge or custom evals, and compare experiments on datasets;
• Debug in a local or self-hosted UI.

For making an agent good, it is a strong choice.

What an observability tool does not give you

Evidence for a regulator, an auditor or a customer must convince someone who does not trust you.

• The operator controls the data. Whoever runs the instance can in principle edit or delete stored traces, so an export is a claim, not proof.
• No independent timestamp or signature. An export shows what the database held when you exported it, not that it looked the same at the time of the incident.
• No mapping onto the AI Act. Logging duties (Art. 12, 19, 26) ask what the logs make traceable, not only what they contain.

None of this is a flaw in Phoenix; it is outside what the tool is for.

What Vetro Attest adds

Vetro Attest accepts an OTLP/JSON trace with the OpenTelemetry GenAI semantic conventions, rebuilds it into a hash-chained ledger and checks it for free. For 49 USD, one-off, you get:

• a full EU AI Act report (Markdown and HTML) mapping the trace onto logging obligations;
• an ed25519 countersignature over the digest, event count and timestamp, verifiable by anyone against our published public key, no account needed.

The countersignature attests that the trace verified at a time. It does not attest that the events are true; the report is a structured aid, not legal advice or certification.

When to use both

• Keep Phoenix to debug, evaluate and improve your agent.
• When a run matters, export its trace as OTLP/JSON and get it countersigned. Store the attestation next to the trace.
• On an audit or dispute, hand over the trace plus the attestation.

Phoenix tells you what your agent did. The countersignature lets someone else believe it.

Try it

• Run the free EU AI Act Art. 12/14 checker.
• Paste an OTLP trace on the Vetro Attest home page and verify it free. The full report plus countersignature is 49 USD, no subscription.

See a sample ledger verified in one click, check your own logs free or get the countersigned EU AI Act report.