Top 5 AI Agent Eval Tools After Promptfoo's Exit

Source: Dev.to

TL;DR

• DeepEval – pytest‑native open‑source evaluation.
• Braintrust – full‑lifecycle eval with CI/CD quality gates.
• Arize Phoenix – vendor‑neutral self‑hosted tracing and eval.
• LangSmith – all‑in on LangChain.
• Comet Opik – budget‑conscious teams running high‑volume traces.

On March 9, OpenAI acquired Promptfoo for $86 M. Promptfoo was the most widely used open‑source LLM eval and red‑team CLI (10.8 k GitHub stars), used by thousands of teams to test prompts, model outputs, and agent behavior across every major provider.

The acquisition raises an immediate question for anyone using non‑OpenAI models: will Promptfoo stay vendor‑neutral? The team says yes, but the incentive structure suggests maybe not.

Whether you are running agents on Nebula, LangGraph, CrewAI, or your own framework, eval tooling is non‑negotiable. Agents that call tools, make decisions, and interact with production systems need automated testing that catches failures before users do.

Below are five independent alternatives – none owned by a model provider.

Comparison Table

DeepEval

DeepEval is a Python‑native eval framework that runs inside pytest. If your team already writes tests with pytest, DeepEval slots in without changing your workflow. Define metrics, write test cases, and run them alongside your existing test suite.

• Metric library: >50 metrics, including 6 agent‑specific ones for DAG evaluation, tool‑call correctness, and multi‑step reasoning.
• Community: 13.9 k GitHub stars, strong momentum and active development.

Strengths

• pytest integration → zero adoption friction for Python teams.
• Write eval tests exactly like unit tests.
• CI/CD integration is free – just add DeepEval tests to your existing pipeline.

Weaknesses

• Python‑only.
• No persistent dashboard unless you pay for Confident AI ($19.99 /user / mo).
• Eval‑only – no production tracing or monitoring; you need a separate tool for runtime observability.

Best for

Python teams that want open‑source eval integrated directly into their test suite and CI pipeline.

Pricing

• Free (open source).
• Confident AI dashboard: $19.99 per user / month.

Braintrust

Braintrust goes beyond evaluation into the full lifecycle: prompt management, eval scoring, CI/CD quality gates, production tracing, and the Loop AI feature that automates prompt optimization.

• CI/CD quality gates: Define minimum score thresholds; Braintrust blocks deployments that fail.
• Customers: Stripe, Notion, and other production‑heavy teams.
• Integrations: 25+ frameworks.

Strengths

• The only tool here that covers eval, production monitoring, and automated prompt optimization in a single platform.
• GitHub Actions integration turns evals from a manual step into an automated safety net.

Weaknesses

• Pro plan at $249 /mo is the most expensive option on this list.
• Free tier (1 M log spans) is generous for prototyping, but production teams will quickly exceed it.
• Self‑hosting is enterprise‑only.

Best for

Teams that want a single platform for the entire eval‑to‑production lifecycle and have the budget for it.

Pricing

• Free tier: 1 M log spans.
• Pro: $249 /mo.
• Enterprise: pricing on request.

Arize Phoenix

Arize Phoenix is built on OpenTelemetry, so it plays nicely with any observability stack you already run. The self‑hosted version is completely free with no feature gating – you get the same capabilities whether you pay or not.

• Dedicated agent evaluators: tool‑call accuracy, retrieval quality, response faithfulness.
• Embedding visualization: spot clustering issues and drift over time.
• Backed by a $70 M Series C; used by Uber and Booking.com.

Strengths

• The most genuinely vendor‑neutral option.
• OTel‑native → traces are portable; no lock‑in.
• Self‑hosting is first‑class, not an enterprise upsell.
• Ideal for data‑residency or compliance requirements.

Weaknesses

• Eval capabilities are less specialized than DeepEval’s metric library.
• Started as an observability tool; eval‑specific features (custom metrics, assertion frameworks) are less mature than purpose‑built eval tools.

Best for

Teams that need self‑hosted, vendor‑neutral tracing and eval, especially those with existing OTel infrastructure or strict compliance needs.

Pricing

• Free self‑hosted (no feature gates).
• Arize Cloud: from $50 /mo.

LangSmith

LangSmith is the eval and observability platform built by the LangChain team. If you are building agents with LangGraph, LangSmith gives you the deepest integration: multi‑turn agent evaluation, step‑level scoring for each node in your graph, and 400‑day trace retention.

• Dataset management & annotation: strong features for building eval datasets from production traces.

Strengths

• Unmatched integration depth with LangGraph and LangChain.
• Provides visibility into every step, tool call, and decision point without extra instrumentation code.

Weaknesses

• Ecosystem lock‑in – works best (and sometimes only) with LangChain‑based agents.
• Pricing of $39/seat / month can add up for larger teams.

Best for

Teams already building with LangGraph or LangChain that want the tightest possible eval and observability integration.

Pricing

• Developer plan: Free
• Pro plan: $39 / seat / month
• Enterprise: On request

Comet Opik

Tagline: “The newest entrant positioning itself on price and scale.”

• Key Features:
  • Agent Optimizer – six optimization algorithms automatically improve prompts and configurations based on eval results.
  • Handles up to 40 M traces per day, ideal for high‑throughput pipelines.
  • Apache 2.0 license → self‑hostable without restrictions.

Strengths

• Best price‑to‑capability ratio on the list.
• Automated prompt tuning closes the loop between “poor score” and “better prompt”.

Weaknesses

• Newer platform → less enterprise traction and a smaller community.
• Agent Optimizer is still early‑stage; results can vary by use case.

Best for

• Budget‑conscious teams needing production‑grade tracing & eval at scale.
• Teams that want a self‑hosted solution with a permissive license.

Pricing

• Free tier available
• Paid plans: Starting at $19 / month

Decision‑Making Framework

Quick Decision Tree

• Open‑source + Python? → DeepEval
• Full lifecycle + CI/CD gates? → Braintrust
• Vendor‑neutral + self‑hosted? → Arize Phoenix
• LangChain ecosystem? → LangSmith
• Budget + high volume? → Comet Opik

Strategic Takeaway

The Promptfoo acquisition reminds us not to depend on a single vendor for critical infrastructure. Your eval tool today could be your model provider, hosting platform, or vector database tomorrow.

All five tools listed are either independent companies or open‑source projects, so your eval infrastructure should survive any single acquisition.

Recommendations by Use‑Case

• Already writing pytest tests for agents? → DeepEval is the fastest path; add eval metrics to your existing test suite in an afternoon.
• Need a complete platform (eval + monitoring + CI/CD quality gates)? → Braintrust is the most mature.
• Self‑hosting is non‑negotiable? → Arize Phoenix gives you everything for free.

Pick one, start testing, and avoid the “agent without eval coverage” pitfall.

Further Reading

• How to Test AI Agent Tool Calls with Pytest – deep dive into code‑level testing.
• Top 5 AI Agent Frameworks for 2026 – see which frameworks pair best with each eval tool.
• Top 5 Code Sandboxes for AI Agents – explore where your agents actually run.