experimentation

experimentation is a skill for Claude Code, Codex from cbrock84/headcount. It costs 68 tokens per session (519 once invoked), scanned A, original, MIT.

A guide to running A/B tests, where two versions are compared with real users, and other controlled experiments. It covers forming a clear hypothesis, choosing measurements, deciding how much data is needed, and interpreting results honestly.

In plain words
What is it for?
Use it to plan experiments, set sample sizes and durations, choose primary and safety metrics, check test quality, and decide whether a result supports action.
Why use it?
It reduces false conclusions caused by small samples, stopping tests too early, or judging success with changing measurements.

Skill for Claude CodeCodex

Part of the demand-generation plugin — 11 skills shipped together

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/cbrock84/headcount/experimentation
Any agent
npx skills add cbrock84/headcount --skill experimentation
Clone the repo
git clone --depth 1 https://github.com/cbrock84/headcount

Made for: Claude Code, Codex.

Or install demand-generation, the plugin that ships this one along with the rest of its 11 skills.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for experimentation

README.md
[![agentmods](https://agentmods.dev/badge/skills/cbrock84/headcount/experimentation.svg)](https://agentmods.dev/skills/cbrock84/headcount/experimentation)
Your own site
<a href="https://agentmods.dev/skills/cbrock84/headcount/experimentation"><img src="https://agentmods.dev/badge/skills/cbrock84/headcount/experimentation.svg" alt="Measured on agentmods" height="20"></a>
Per session 68 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 519 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00068 $0.00519
Opus 5 $0.00034 $0.00260
Sonnet 5 $0.00014 $0.00104
Haiku 4.5 $0.00007 $0.00052

Measured 4d ago against content hash dbf3251dc3d6, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

experimentation scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 4d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

plugins/demand-generation/skills/experimentation/SKILL.md · 49 lines

How it starts

The opening of the file, as written. The whole thing — 49 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Experimentation

Most A/B testing programs produce confident conclusions from insufficient data. The discipline is almost entirely in what you do before launch.

Before running

  • Hypothesis with a mechanism. "Moving the pricing table above the fold will raise trial starts, because visitors currently leave before seeing pricing." Not "let's try a green button."
  • One primary metric, chosen in advance. Secondary metrics are context, never the verdict.
  • Sample size calculated in advance, from your baseline rate and the smallest lift that would change a decision. If the required sample is unreachable, do not run the test — decide by judgment and say so.
  • Duration set in advance, covering at least one full weekly cycle, and two if the buying cycle is long.
  • Guardrail metrics that would make you reject a win: refunds, support volume, downstream retention.

While running

Do not look at results and act on them mid-flight. Peeking and stopping at significance is the single most common way to generate false positives, and it is very effective at it.

Check only that the test is running correctly — even split, no broken variant, tracking firing.

Reading

  • At the pre-set duration, not before, and not extended because it is nearly significant. Extending until significance manufactures it.
  • Significance is not size. A statistically significant 0.3% lift may not be worth shipping.
  • Inconclusive is a real result and the most common one. It means the change did not matter enough to detect, which is useful.
  • Check the guardrails before declaring a win.
  • Segment afterward for hypotheses only, never for verdicts. Slice enough ways and something is always significant.

Program level

Test where the traffic and the leverage are. Most sites can only run a handful of adequately powered tests a year — spend them on structural questions, not button colors.

Keep a log of every test: hypothesis, result, decision. Without it, teams re-run the same tests every eighteen months and re-learn the same things.

Read the full file on GitHub · 49 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 4d ago First seen · 49 lines · 68 tokens per session scan A dbf3251dc3d6

Subscribe to this mod's changes

experimentation is a skill published in the GitHub repository cbrock84/headcount (578 stars, last pushed 4d ago), licensed MIT. It adds 68 tokens to every session and 519 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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