Francisco Perez Sorrosal Praxion Agent Evals

Agent Evals

Evaluate AI agent behavior systematically. Agent evals differ fundamentally from traditional software tests -- they handle non-determinism, multi-dimensional scoring, and multiple valid solution paths. This skill covers the full eval lifecycle: design, implement, run, iterate, and integrate into CI/CD.

Satellite files (loaded on-demand):

• references/framework-patterns.md -- framework comparison, Python code examples for Inspect AI, DeepEval, Promptfoo
• references/typescript.md -- TypeScript eval tooling: Vitest async patterns for LLM calls, Promptfoo YAML schema, TypeScript provider config, CLI vs SDK usage
• references/eval-design-patterns.md -- golden datasets, LLM-as-judge, grader design, scoring, non-determinism
• references/cicd-integration.md -- GitHub Actions workflows, deployment gates, regression tracking, cost management
• references/run-ledger-schema.md -- run_store_descriptor, EVAL_RESULTS.md schema (13 fields), EVAL_LOG.md aggregate columns (11 cols), verifier reuse
• references/data-governance.md -- held-out split design, MANIFEST.json schema (sha256/version/source/split), answer-key isolation, eval determinism practices, contamination detection

Gotchas

• Non-determinism is not a bug, it's the medium. Never expect exact output matching. Use rubrics, partial credit, and statistical aggregation. A single trial tells you almost nothing.

• 0% pass rate usually means broken eval, not broken agent. Verify tasks are solvable by running them manually with a reference solution. Check grader fairness before blaming the agent.

• Grading outcomes, not paths, is harder than it sounds. An agent that uses 3 tools instead of your expected 2 may still be correct. Default to lenient trajectory matching (unordered or subset) unless ordering genuinely matters.

• LLM-as-judge needs calibration, not blind trust. Validate model graders against human judgments regularly. Few-shot prompting increases consistency from ~65% to ~78%. Use structured rubrics with explicit scoring criteria.

• Cost surprises compound with trials. Running 50 test cases x 5 trials x LLM grading = 250+ API calls per eval run. Budget upfront. Use tiered execution: full suite nightly, critical subset on PR.

• temperature=0 does not guarantee determinism. Research confirms non-determinism persists even at zero temperature. Always run multiple trials and report both pass@k and pass^k.

• Golden datasets rot. As the agent improves, easy evals saturate and stop providing signal. Grow the dataset continuously and retire saturated cases to the regression suite.

• Don't eval what you can assert. If a check is deterministic (JSON schema validation, test suite execution, file existence), use a code-based grader. Reserve LLM grading for genuinely subjective or nuanced dimensions.

• Sandboxing is not optional for tool-using agents. Agents with file system or shell access can cause real damage during evals. Use Docker containers, temp directories, or git checkpoints.

• Skip transcript review at your peril. Graders can be wrong in both directions -- passing bad outputs and failing good ones. Regular transcript review builds intuition and catches grader drift.

Why Agent Evals Differ from Traditional Tests

Evaluation-Driven Development (EDD) extends TDD/BDD for non-deterministic systems. Define evals for planned capabilities before implementation, run them continuously, and use failures to drive improvement -- the same test-first philosophy, adapted for agents.

Eval Types

By Scope

By Purpose

As agents improve, high-performing capability evals graduate into regression suites. Monitor saturation -- when agents pass all solvable tasks, add harder variants.

Getting Started: Zero to First Eval

Anthropic's roadmap from zero to reliable evals, condensed:

1. Start with 20-50 tasks from real failures. Production failures make better evals than synthetic scenarios. Don't wait for perfect datasets -- early evals gain traction quickly due to large effect sizes.

2. Write unambiguous tasks with reference solutions. Tasks must be solvable by competent agents. A 0% pass@100 usually signals broken tasks, not incapable agents.

3. Build balanced problem sets. Test both "should do" and "shouldn't do" cases. Avoid class imbalance -- test both undertriggering and overtriggering.

4. Set up clean environments per trial. Each run starts from a fresh state. Shared state between runs introduces correlated failures from infrastructure flakiness.

5. Design thoughtful graders. Prefer deterministic graders where possible; use LLM graders for flexibility; employ human graders for calibration. Grade outcomes, not paths.

6. Read transcripts. Review trial transcripts to verify graders work as intended. Surface genuine agent mistakes versus false rejections.

7. Graduate capability evals to regression suites. When a capability eval consistently passes, promote it to the regression suite where it must maintain ~100%.

8. Maintain evals as living artifacts. Same rigor as production code. Grow the dataset with every bug fix and capability addition.

Framework Selection

Three primary Python-friendly frameworks, each with distinct strengths:

Selection Guidance

--> See references/framework-patterns.md for code examples and detailed comparison across all frameworks.

Core Eval Concepts

Grader Types

Layered strategy: Code-based first (cheap, deterministic), LLM fallback for what code cannot assess, human calibration to validate both. Mature teams combine all three.

Scoring Approaches

Non-Determinism Handling

The fundamental challenge: same input may produce different valid outputs across runs. Even temperature=0 does not guarantee determinism.

• Run 3-5 trials minimum per test case (10+ for high-variance outputs)
• Report pass@k (probability of success in k attempts, optimistic) and pass^k (probability all k succeed, pessimistic)
• Gaps up to 24.9 percentage points between pass@k and pass^k are documented
• Use statistical aggregation over individual assertions
• Implement anomaly detection for trend monitoring across runs

--> See references/eval-design-patterns.md for full patterns on golden datasets, LLM-as-judge, grader design, and metrics.

Agent-Specific Challenges

Tool Use Evaluation

Agent tool use requires evaluating correct selection, parameter construction, call ordering, and failure handling. Three approaches by strictness:

• Strict trajectory match: exact tool call sequence must match reference
• Unordered match: correct tools called, order does not matter
• Subset/superset match: agent may call additional valid tools or skip optional ones

Grade outcomes, not exact trajectories -- agents may find valid tool combinations the eval designer did not anticipate.

Trajectory Evaluation

Choose the right scope for the behavior being tested:

• Final response only: when only the outcome matters (answer correctness)
• Trajectory: when the path matters (tool selection, reasoning quality, efficiency)
• Single step: when isolating one decision point (~50% of cases need only this)
• Full end-to-end: when environment interaction matters (file changes, API calls, state mutations)

Cost and Latency Tracking

Track as first-class metrics alongside correctness:

• Token usage per task: total input + output tokens consumed
• Cost per successful outcome: total cost / successful completions
• Latency percentiles: p50, p95, p99 end-to-end and per-step
• Turn count: steps taken to reach solution (efficiency proxy)

Set budgets and alerts -- if an agent uses 10x expected tokens, something is wrong.

Statefulness

Deep agents maintain state across interactions. For reproducible evals:

• Start each trial from a clean environment (temp directories, Docker containers, git checkpoints)
• Evaluate state artifacts (generated files, modified configs) alongside responses
• Use the VCR pattern (record/replay) for external API calls to improve speed and reproducibility

CI/CD Integration

Integrate evals at three levels:

1. Eval-on-commit: regression suite on every relevant change (prompts, model configs, agent logic, tool definitions)
2. PR-level reporting: post eval results as PR comments with score breakdowns and baseline comparison
3. Deployment gates: block deployment if eval scores drop below thresholds

Cost management: run full suite nightly, critical subset on every PR, smoke tests on commit.

--> See references/cicd-integration.md for complete GitHub Actions workflows and deployment gate patterns.

Eval-Driven Development Workflow

Apply EDD alongside TDD/BDD in agentic projects:

1. Identify the behavior -- define what the agent should do (from acceptance criteria or user failures)
2. Write the eval -- create test cases with inputs, expected outcomes, and grading criteria
3. Establish baseline -- run against current agent, measure pass rate
4. Implement the change -- modify prompts, tools, or logic
5. Run evals -- compare against baseline, check for regressions
6. Iterate -- refine until target pass rates are met across trials
7. Graduate -- move passing capability evals to the regression suite

This mirrors the spec-driven-development skill's behavioral specification workflow, with evals replacing deterministic assertions.

Cross-Skill References

• python-development -- pytest patterns, test organization, and code quality tools for eval implementations
• typescript-development -- TypeScript conventions and baseline setup; see also references/typescript.md for Vitest + Promptfoo eval patterns specific to TypeScript projects
• agentic-sdks -- agent building patterns (the systems you are evaluating); SDK-specific testing hooks
• spec-driven-development -- behavioral specifications and acceptance criteria inform eval design; REQ IDs thread into eval case naming
• llm-prompt-engineering -- single-prompt regression-assertion design (Promptfoo YAML, DeepEval pytest, LLM-judge bias mitigations); see references/prompt-testing.md. This skill (agent-evals) owns the full eval harness and agent-level metric design; llm-prompt-engineering owns prompt-level test authoring

Resources

Primary References

• Anthropic: Demystifying Evals for AI Agents -- comprehensive guide from zero to reliable evals
• Anthropic: Building Effective Agents -- eval-driven development philosophy

Framework Documentation

• Inspect AI -- UK AISI evaluation framework (used by Anthropic, DeepMind)
• DeepEval -- pytest-native LLM evaluation
• Promptfoo -- agent eval with Claude/Codex SDK support

Research

• EDDOps: Evaluation-Driven Development -- process model for eval-driven LLM development
• On Randomness in Agentic Evals -- statistical analysis of non-determinism
• LangChain: Evaluating Deep Agents -- practical lessons from production

Source: francisco-perez-sorrosal/praxion — distributed by TomeVault.