ab-harness

Measures whether a Claude Code setup improves task outcomes via counterfactual A/B and layered-ablation runs.

1|Updated Apr 16, 2026
One-click install
npx skills add https://github.com/wan-huiyan/claude-ecosystem-hygiene --skill ab-harness-wan-huiyan
Or copy as Structured Prompt for Agent
Please help me install this Agent Skill.
Skill: ab-harness
Source: https://github.com/wan-huiyan/claude-ecosystem-hygiene/tree/main/plugins/ab-harness
Command: npx skills add https://github.com/wan-huiyan/claude-ecosystem-hygiene --skill ab-harness-wan-huiyan

SYSTEM DOCUMENTATION & REQUIREMENTS

What problem does it solve? Reference counts and usage audits show which parts of your ~/.claude setup get touched, but not whether they actually improve answers. This Skill runs controlled experiments — the same tasks with your full setup versus a clean environment — to quantify the real impact of your memories, lessons, axioms, skills, and hooks on turns, tool calls, cost, and pitfall prevention. ## Core Features & Use Cases - Binary A/B testing: Run matched tasks with setup-ON versus setup-OFF using CLAUDE_CONFIG_DIR isolation, with pinned model, permission mode, and stdin controls for fair comparison. - Layered ablation: Strip one layer at a time (CLAUDE.md, axioms, lessons, skills/plugins, auto-memory, in-repo docs) across 12 cells to rank which layers actually prevent pitfalls. - JSONL transcript mining: Extract turn counts, tool-call histograms, files read, skills invoked, and pitfall keyword hits from session logs, with recovery from rate-limit stubs and orchestration race conditions. - Use Case: After an ecosystem audit flags your HOT artifacts, run this harness on 3-15 tasks to produce an honest report showing colleagues whether your setup saves turns, prevents pitfalls, or is pure overhead — then feed the ranked layer list to memory-hygiene for pruning decisions. ## Quick Start Ask the AI to run an A/B test comparing your current Claude Code setup against a clean environment on a few representative tasks and report the difference in turns, cost, and pitfall prevention.

Frequently Asked Questions about ab-harness

High-intent search queries and answers about installing and using this skill.

FAQPage Schema
How do I A/B test my Claude Code setup?

Run each task twice with identical prompts: once normally and once with CLAUDE_CONFIG_DIR pointed at an empty directory. Pin the model, use --permission-mode bypassPermissions, redirect stdin from /dev/null, and compare turns, tool calls, cost, and pitfall hits from the JSON output.

What is the difference between binary A/B and layered ablation?

Binary A/B compares full setup versus clean environment to measure overall value, costing about $2-10. Layered ablation strips one layer at a time across 12 cells to rank which specific layers (skills, lessons, CLAUDE.md, docs) prevent pitfalls, costing $11-80 depending on runs per cell.

Does CLAUDE_CONFIG_DIR fully isolate the clean environment?

No. It isolates global CLAUDE.md, axioms, skills, hooks, and project auto-memory, but in-repo files like docs/runbooks and MEMORY.md remain visible. The harness measures the marginal value of the ~/.claude layers, not the total setup.

Why did my orchestrator lose run outputs during parallel execution?

The CLI opens output files with truncate semantics, so racing subprocesses can zero out completed runs. Treat the per-session JSONL transcript as ground truth, avoid wait -n on older bash, and add rate-limit stub detection before re-running cells.

When should I not use this A/B harness?

Skip it for quick checks — it costs $10+ and 30 minutes to 3 hours. Use cheaper scans like ecosystem-audit for utilization questions first, and only run this harness when you need counterfactual evidence that artifacts change outcomes.

How many tasks do I need for reliable A/B results?

n=3 is a pilot that provides evidence, not proof. Target n>=5 tasks for a real effect-size estimate, and always declare the sample size, task selection bias, and single-shot variance in the report.