lemma-leakage

lemma-leakage is a skill for Claude Code from tkpratardan/lemma. It costs 31 tokens per session (236 once invoked), scanned A, original, MIT.

A guide for checking whether a machine-learning dataset or evaluation pipeline accidentally uses information that would not be available when making a real prediction. It covers target, preprocessing, time, group, and sampling leakage.

In plain words
What is it for?
Use it to inspect features, missing values, data splits, duplicate entities, time-based data, preprocessing steps, source overlap, and outcome-dependent sampling.
Why use it?
It prevents inflated test scores caused by hidden information sharing between training data and evaluation data.

Skill for Claude Code

Written for Claude Code: shipped in a Claude Code plugin.

Part of the lemma plugin — 10 skills, 6 hooks, 1 MCP server shipped together

Good fit Use it to inspect features, missing values, data splits, duplicate entities, time-based data, preprocessing steps, source overlap, and outcome-dependent sampling.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/tkpratardan/lemma/lemma-leakage
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.

Any agent
npx skills add tkpratardan/lemma --skill lemma-leakage
Clone the repo
git clone --depth 1 https://github.com/tkpratardan/lemma

Made for: Claude Code.

Or install lemma, the plugin that ships this one along with the rest of its 10 skills, 6 hooks, 1 MCP server.

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 lemma-leakage

README.md
[![agentmods](https://agentmods.dev/badge/skills/tkpratardan/lemma/lemma-leakage/github.svg)](https://agentmods.dev/skills/tkpratardan/lemma/lemma-leakage)
Your own site
<a href="https://agentmods.dev/skills/tkpratardan/lemma/lemma-leakage"><img src="https://agentmods.dev/badge/skills/tkpratardan/lemma/lemma-leakage/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for lemma-leakage

Your own site · 80×15
<a href="https://agentmods.dev/skills/tkpratardan/lemma/lemma-leakage"><img src="https://agentmods.dev/badge/skills/tkpratardan/lemma/lemma-leakage.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 31 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 236 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
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 5.1 $0.00031 $0.00236
Opus 5 $0.00015 $0.00118
Sonnet 5 $0.00006 $0.00047
Haiku 4.5 $0.00003 $0.00024

Measured 9d ago against content hash f06d0694d3f9, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-09, from the pricing page.

Security

Grade A, and why

lemma-leakage 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 9d 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.

.openclaw/skills/lemma-leakage/SKILL.md · 32 lines

What it actually says

Leakage audit

Deliver

Rank leakage findings by severity and show reproducible before/after scores, the contaminated path, the corrected validation design, and remaining risk.

Check

  • Reconstruct information available at the real prediction moment.
  • Audit features and missingness for target proxies and post-outcome facts.
  • Verify that imputers, encoders, selection, and scaling are fit within each training fold.
  • Check time travel, repeated entities, near duplicates, source overlap, and outcome-dependent sampling.
  • Remove suspicious features or strengthen the split and compare with a simple baseline.

Do not rationalize an implausible score, rely only on feature importance, randomly split temporal or repeated-entity data, or continue tuning before material leakage is resolved.

For the full leakage taxonomy, read references/deep-guide.md.

Files

What ships with it

1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

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. 9d ago First seen · 32 lines · 31 tokens per session scan A f06d0694d3f9

Subscribe to this mod's changes

lemma-leakage is a skill published in the GitHub repository tkpratardan/lemma (3 stars, last pushed 29d ago), licensed MIT. It adds 31 tokens to every session and 236 once invoked, about $0.0002 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 2026-08-31.

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