Agent skill

Eval Harness

by affaan-m in affaan-m/ECC

Eval-driven development (EDD) framework for AI coding sessions — define capability and regression evals before coding, grade with code-based, model-based, rule, or human graders, and track pass@k…

MITAuto-check passedAI & LLM Engineering

Install Eval Harness

skills CLI
$ npx skills add affaan-m/ECC --skill eval-harness -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI
$ gh skill install affaan-m/ECC eval-harness --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy
$ git clone --depth 1 https://github.com/affaan-m/ECC.git skills-src && mkdir -p .claude/skills && cp -r skills-src/skills/eval-harness .claude/skills/eval-harness && rm -rf skills-src

Use ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.

Claude Code skills documentation · loads skills from .claude/skills/

Facts

Skill name
eval-harness
GitHub stars
276k
Token cost
~2.2k tokens
SKILL.md length
641 words
Files
1
Skills in repo
683
Repo updated
First seen
Licence
MIT

At a glance

Eval-driven development (EDD) framework for AI coding sessions — define capability and regression evals before coding, grade with code-based, model-based, rule, or human graders, and track pass@k…

  • Works in 7 steps: Code-Based Grader → Model-Based Grader → Human Grader → …
  • Defining pass/fail criteria for agent tasks
  • SKILL.md covers When to Activate, Philosophy, Eval Types and Grader Types, plus 8 more sections
  • Calls npm and node

What it does

Eval Harness is an agent skill from affaan-m/ECC. Eval-driven development (EDD) framework for AI coding sessions — define capability and regression evals before coding, grade with code-based, model-based, rule, or human graders, and track pass@k and pass^k reliability. Use when defining pass/fail criteria for agent tasks, measuring agent reliability, building regression suites for prompt or agent changes, or benchmarking across model versions.

Its SKILL.md is about 2.2k tokens, which your agent loads only when the skill is triggered. It is a single SKILL.md file with no bundled scripts.

It sits in AI & LLM Engineering, covering LLM evaluation. The repository describes itself as: The agent harness performance optimization system. Skills, instincts, memory, security, and research-first development for Claude Code, Codex, Opencode, Cursor and beyond. The licence is MIT.

When your agent uses it

  • Defining pass/fail criteria for agent tasks
  • Measuring agent reliability
  • Building regression suites for prompt
  • Benchmarking across model versions

Example prompts

  • “/eval-harness”

Workflow steps

7 steps, taken from the step headings in SKILL.md.

  1. Code-Based Grader
  2. Model-Based Grader
  3. Human Grader
  4. Define (Before Coding)
  5. Implement
  6. Evaluate
  7. Report

What it can do on your machine

Read from SKILL.md and the folder at commit 4eb71d9. It shows what the files ask for, not the result of running them.

  • Tool permissions

    Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

    From allowed-tools in the SKILL.md frontmatter.

  • Runs code

    Shell commands in SKILL.md call:

    • npm
    • node

    From the folder's file list and the shell code blocks in SKILL.md.

  • Network

    No URLs in SKILL.md. Its commands use npm, which can reach the network depending on how they are called.

    From URLs in SKILL.md, links to its own repository left out.

  • Credentials

    Names no API keys, tokens, secrets or passwords.

    From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Eval Harness loads about 2.2k tokens when it runs. Until then it costs about 103 tokens; SKILL.md has 641 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~103
When it runs · the whole SKILL.md, loaded when a task matches
~2.2k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Auto-check passed

The automated check found no risky patterns in SKILL.md.

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from affaan-m/ECC at commit 4eb71d9, republished under its MIT licence (© affaan-m). 641 words, ~2,184 tokens.

Download SKILL.mdSave it as .claude/skills/eval-harness/SKILL.md (or your agent's skills folder).
name
eval-harness
description
Eval-driven development (EDD) framework for AI coding sessions — define capability and regression evals before coding, grade with code-based, model-based, rule, or human graders, and track pass@k and pass^k reliability. Use when defining pass/fail criteria for agent tasks, measuring agent reliability, building regression suites for prompt or agent changes, or benchmarking across model versions.
metadata.origin
ECC
tools
Read, Write, Edit, Bash, Grep, Glob

Eval Harness Skill

A formal evaluation framework for Claude Code sessions, implementing eval-driven development (EDD) principles.

When to Activate

  • Setting up eval-driven development (EDD) for AI-assisted workflows
  • Defining pass/fail criteria for Claude Code task completion
  • Measuring agent reliability with pass@k metrics
  • Creating regression test suites for prompt or agent changes
  • Benchmarking agent performance across model versions

Philosophy

Eval-Driven Development treats evals as the "unit tests of AI development":

  • Define expected behavior BEFORE implementation
  • Run evals continuously during development
  • Track regressions with each change
  • Use pass@k metrics for reliability measurement

Eval Types

Capability Evals

Test if Claude can do something it couldn't before:

markdown
[CAPABILITY EVAL: feature-name]
Task: Description of what Claude should accomplish
Success Criteria:
  - [ ] Criterion 1
  - [ ] Criterion 2
  - [ ] Criterion 3
Expected Output: Description of expected result
Regression Evals

Ensure changes don't break existing functionality:

markdown
[REGRESSION EVAL: feature-name]
Baseline: SHA or checkpoint name
Tests:
  - existing-test-1: PASS/FAIL
  - existing-test-2: PASS/FAIL
  - existing-test-3: PASS/FAIL
Result: X/Y passed (previously Y/Y)

Grader Types

1. Code-Based Grader

Deterministic checks using code:

bash
# Check if file contains expected pattern
grep -q "export function handleAuth" src/auth.ts && echo "PASS" || echo "FAIL"

# Check if tests pass
npm test -- --testPathPattern="auth" && echo "PASS" || echo "FAIL"

# Check if build succeeds
npm run build && echo "PASS" || echo "FAIL"
2. Model-Based Grader

Use Claude to evaluate open-ended outputs:

markdown
[MODEL GRADER PROMPT]
Evaluate the following code change:
1. Does it solve the stated problem?
2. Is it well-structured?
3. Are edge cases handled?
4. Is error handling appropriate?

Score: 1-5 (1=poor, 5=excellent)
Reasoning: [explanation]
3. Human Grader

Flag for manual review:

markdown
[HUMAN REVIEW REQUIRED]
Change: Description of what changed
Reason: Why human review is needed
Risk Level: LOW/MEDIUM/HIGH

Metrics

pass@k

"At least one success in k attempts"

  • pass@1: First attempt success rate
  • pass@3: Success within 3 attempts
  • Typical target: pass@3 > 90%
pass^k

"All k trials succeed"

  • Higher bar for reliability
  • pass^3: 3 consecutive successes
  • Use for critical paths

Eval Workflow

1. Define (Before Coding)
markdown
## EVAL DEFINITION: feature-xyz

### Capability Evals
1. Can create new user account
2. Can validate email format
3. Can hash password securely

### Regression Evals
1. Existing login still works
2. Session management unchanged
3. Logout flow intact

### Success Metrics
- pass@3 > 90% for capability evals
- pass^3 = 100% for regression evals
2. Implement

Write code to pass the defined evals.

3. Evaluate
bash
# Run capability evals
[Run each capability eval, record PASS/FAIL]

# Run regression evals
npm test -- --testPathPattern="existing"

# Generate report
4. Report
markdown
EVAL REPORT: feature-xyz
========================

Capability Evals:
  create-user:     PASS (pass@1)
  validate-email:  PASS (pass@2)
  hash-password:   PASS (pass@1)
  Overall:         3/3 passed

Regression Evals:
  login-flow:      PASS
  session-mgmt:    PASS
  logout-flow:     PASS
  Overall:         3/3 passed

Metrics:
  pass@1: 67% (2/3)
  pass@3: 100% (3/3)

Status: READY FOR REVIEW

Integration Patterns

Pre-Implementation
/eval define feature-name

Creates eval definition file at .claude/evals/feature-name.md

During Implementation
/eval check feature-name

Runs current evals and reports status

Post-Implementation
/eval report feature-name

Generates full eval report

Eval Storage

Store evals in project:

.claude/
  evals/
    feature-xyz.md      # Eval definition
    feature-xyz.log     # Eval run history
    baseline.json       # Regression baselines

Best Practices

  1. Define evals BEFORE coding - Forces clear thinking about success criteria
  2. Run evals frequently - Catch regressions early
  3. Track pass@k over time - Monitor reliability trends
  4. Use code graders when possible - Deterministic > probabilistic
  5. Human review for security - Never fully automate security checks
  6. Keep evals fast - Slow evals don't get run
  7. Version evals with code - Evals are first-class artifacts

Example: Adding Authentication

markdown
## EVAL: add-authentication

### Phase 1: Define (10 min)
Capability Evals:
- [ ] User can register with email/password
- [ ] User can login with valid credentials
- [ ] Invalid credentials rejected with proper error
- [ ] Sessions persist across page reloads
- [ ] Logout clears session

Regression Evals:
- [ ] Public routes still accessible
- [ ] API responses unchanged
- [ ] Database schema compatible

### Phase 2: Implement (varies)
[Write code]

### Phase 3: Evaluate
Run: /eval check add-authentication

### Phase 4: Report
EVAL REPORT: add-authentication
==============================
Capability: 5/5 passed (pass@3: 100%)
Regression: 3/3 passed (pass^3: 100%)
Status: SHIP IT
Show full SKILL.md (352 more words)Show less

Local Framework Utilities

The mechanical utilities ship in scripts/lib/eval-harness/:

sh
node scripts/eval-harness.js example
  • Capsule: hash-linked journal with five lineages and local integrity checks.
  • Inspection: source digests, validated variant paths, and syntactic warnings.
  • Replay: declared tools and content-addressed fixtures. Missing fixtures fail closed; SE3 and above are refused in replay. Record mode invokes the registered implementation, so only register trusted functions.
  • Receipt: offline verification of capsule and artifact bytes, with named checks.
  • Retrospective preparation: node scripts/eval-harness.js capsule group <dir> [<dir> ...] groups 1 to 100 explicitly selected, verified local capsule snapshots from one task family by declared harness version. Repeated snapshots count once; conflicting identities or invalid capsules reject the whole report. This is read-only record counting, with no new rollouts, scores or promotion. Use small, quiescent capsules. Payloads, directory arguments and raw run/capsule IDs are omitted, but task-family/version labels are verbatim and digest references are linkable; review them before sharing. Operational validation remains pending.

Candidate execution is disabled on every OS because no verified OS containment backend is implemented. gate run, runGate, runVariant, direct child launch, and the retired effect preload refuse with gate.isolation_required. No trust flag or caller-supplied executor can bypass the refusal. The example records that refusal and inspects source without executing or scoring it.

Do not present static warnings, a capsule receipt, or successful utility tests as candidate containment or promotion evidence. A future gate requires an independently reviewed OS boundary, protected checker and audit channels, and fatal baseline rejection. See docs/architecture/eval-harness-frameworks.md.

Product Evals (v1.8)

Use product evals when behavior quality cannot be captured by unit tests alone.

Grader Types
  1. Code grader (deterministic assertions)
  2. Rule grader (regex/schema constraints)
  3. Model grader (LLM-as-judge rubric)
  4. Human grader (manual adjudication for ambiguous outputs)
pass@k Guidance
  • pass@1: direct reliability
  • pass@3: practical reliability under controlled retries
  • pass^3: stability test (all 3 runs must pass)

Recommended thresholds:

  • Capability evals: pass@3 >= 0.90
  • Regression evals: pass^3 = 1.00 for release-critical paths
Eval Anti-Patterns
  • Overfitting prompts to known eval examples
  • Measuring only happy-path outputs
  • Ignoring cost and latency drift while chasing pass rates
  • Allowing flaky graders in release gates
Minimal Eval Artifact Layout
  • .claude/evals/<feature>.md definition
  • .claude/evals/<feature>.log run history
  • docs/releases/<version>/eval-summary.md release snapshot

© affaan-m, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

Just SKILL.md in skills/eval-harness of affaan-m/ECC.

Open the folder on GitHubat commit 4eb71d9

Compare with similar skills

Eval Harness next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.

Eval Harness compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Eval Harness this skillaffaan-m/ECC276k—~2.2kAutomated safety check: PassMIT
LLM Benchmarking with lm-evaluation-harnessOrchestra-Research/AI-Research-SKILLs13k8 repos~3kAutomated safety check: PassMIT
Hugging Face Local Model Evalshuggingface/skills11k2 repos~1.6kAutomated safety check: PassApache-2.0
Looperksimback/looper710—~2.7kAutomated safety check: NotesMIT
Agent Eval Engineeringlangchain-ai/langchain-skills1.3k—~4kAutomated safety check: PassMIT
Quality FlywheelGoogleCloudPlatform/vertex-ai-samples792—~2kAutomated safety check: PassApache-2.0

Similar skills

  • LLM Benchmarking with lm-evaluation-harness

    Orchestra-Research/AI-Research-SKILLs

    Runs lm-evaluation-harness to benchmark language models on academic suites such as MMLU, GSM8K and HumanEval, compare models and track training checkpoints.

    13k GitHub starsUsed in 8 repos~3k tokens
    AI & LLM EngineeringAuto-check passed
  • Official

    Runs evaluations of Hugging Face Hub models on local hardware with inspect-ai or lighteval, and helps choose between vLLM, Transformers and accelerate backends.

    11k GitHub starsUsed in 2 repos~1.6k tokens
    AI & LLM EngineeringAuto-check passed
  • Looper

    ksimback/looper

    Scaffold a well-designed agent loop with best-practice coaching and a cross-model review council.

    710 GitHub stars~2.7k tokensUpdated 2 mo ago
    AI & LLM EngineeringAuto-check: notes
  • Agent Eval Engineering

    langchain-ai/langchain-skills

    Official

    Builds agent evaluations in stages: inspect the repository and traces, agree a Task Spec with you, then build, audit and run a Harbor task with an independent verifier.

    1.3k GitHub stars~4k tokensUpdated 2 days ago
    AI & LLM EngineeringAuto-check passed
  • Quality Flywheel

    GoogleCloudPlatform/vertex-ai-samples

    Evaluate and improve GenAI models and agents using the Google GenAI Evaluation SDK.

    792 GitHub stars~2k tokensUpdated yesterday
    AI & LLM EngineeringAuto-check passed
  • Eval Harness

    cloudnative-co/claude-code-starter-kit

    Formal evaluation framework for Claude Code sessions implementing eval-driven development (EDD) principles.

    153 GitHub starsUsed in 9 repos~1.3k tokens
    AI & LLM EngineeringAuto-check passed

More from affaan-m/ECC

All 682 skills in this repo
  • Skill Stocktake

    affaan-m/ECC

    Audits your installed Claude skills and commands for quality, with a quick mode for recently changed skills and a full mode that evaluates all of them through subagents.

    277k GitHub starsUsed in 5 repos~3.1k tokens
    Auto-check passed
  • Ingests, indexes, searches, edits and monitors video, audio and live streams through the VideoDB Python SDK, returning stream links, clips and timestamps.

    277k GitHub starsUsed in 3 repos~3.5k tokens
    Auto-check: notes
  • Docs Governance

    affaan-m/ECC

    Route broad documentation-governance requests to existing ECC skills and run an opt-in, read-only audit of mapped documentation roles, links, ADR indexes, and evidence references.

    277k GitHub stars~1.1k tokensUpdated today
    Auto-check passed
  • Rules Distillation

    affaan-m/ECC

    Scans installed skills for principles that recur across them and proposes rule-file changes: append, revise, add a section, create a file or leave as covered.

    277k GitHub starsUsed in 2 repos~2.3k tokens
    Auto-check passed
  • Builds DRAFT counterparty agreements from one markdown template and a small JSON spec per party, with clauses picked by the party's role.

    277k GitHub stars~2.9k tokensUpdated today
    Auto-check passed
  • Set an ECC-specific frontend design direction for production UI work.

    277k GitHub starsUsed in 1 repo~2.2k tokens
    Auto-check passed

Questions about Eval Harness

What does Eval Harness do?

Eval-driven development (EDD) framework for AI coding sessions — define capability and regression evals before coding, grade with code-based, model-based, rule, or human graders, and track pass@k…. Eval Harness is an agent skill from affaan-m/ECC. Eval-driven development (EDD) framework for AI coding sessions — define capability and regression evals before coding, grade with code-based, model-based, rule, or human graders, and track pass@k and pass^k reliability.

When should I use Eval Harness?

Eval Harness fits situations like: defining pass/fail criteria for agent tasks; measuring agent reliability; building regression suites for prompt; benchmarking across model versions.

How do I install Eval Harness in Claude Code?

Run `npx skills add affaan-m/ECC --skill eval-harness -a claude-code`. Or copy the skill folder (skills/eval-harness in affaan-m/ECC) into .claude/skills/eval-harness in your project. Claude Code loads it when a task matches its description.

How do I install Eval Harness in Codex?

Run `npx skills add affaan-m/ECC --skill eval-harness -a codex`. Or copy the skill folder (skills/eval-harness in affaan-m/ECC) into .agents/skills/eval-harness in your project. Codex loads it when a task matches its description.

Can I use Eval Harness in Cursor, Gemini CLI or GitHub Copilot?

Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add affaan-m/ECC --skill eval-harness -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/eval-harness, .gemini/skills/eval-harness, .github/skills/eval-harness and .opencode/skills/eval-harness in your project.

What does Eval Harness need to run?

Going by SKILL.md and its folder, Eval Harness needs the command-line tools its instructions call (npm and node).

Does Eval Harness access the network?

SKILL.md contains no URLs. Its commands use npm, which can reach the network depending on how they are called. This is read from the text; nothing was executed.

Is Eval Harness safe to install?

Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.

What licence does Eval Harness use?

Eval Harness is published under the MIT licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.

How many tokens does Eval Harness use?

About 2.2k tokens (SKILL.md is roughly 8.7k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.

What are the alternatives to Eval Harness?

Skills that share tags, products or a category with Eval Harness: LLM Benchmarking with lm-evaluation-harness (Orchestra-Research/AI-Research-SKILLs, 13k stars), Hugging Face Local Model Evals (huggingface/skills, 11k stars), Looper (ksimback/looper, 710 stars) and Agent Eval Engineering (langchain-ai/langchain-skills, 1.3k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Eval Harness?

affaan-m (a GitHub user) maintains it in affaan-m/ECC, which has 276,111 GitHub stars. The repository holds 683 skills in this directory. The repository was last updated on October 10, 2026.

Source: affaan-m/ECC on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.