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Agent skill

Fill

by leanEthereum in leanEthereum/leanSpec

“Generate consensus layer test fixtures”

— description from SKILL.md by leanEthereum
MITAuto-check passedTesting & QA

Install Fill

skills CLI
$ npx skills add leanEthereum/leanSpec --skill fill -a claude-code

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

GitHub CLI
$ gh skill install leanEthereum/leanSpec fill --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/leanEthereum/leanSpec.git skills-src && mkdir -p .claude/skills && cp -r skills-src/.claude/skills/fill .claude/skills/fill && 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
fill
GitHub stars
143
Token cost
~202 tokens
SKILL.md length
89 words
Files
1
Skills in repo
9
Repo updated
First seen
Licence
MIT

At a glance

  • Works in 3 steps: Discovers tests in tests/consensus/ → Executes spec tests to generate fixtures → Outputs JSON fixtures to…
  • SKILL.md covers Default Usage, Options and What It Does
  • Calls uv and just

About this skill

Fill is a skill in leanEthereum/leanSpec (143 stars). Its SKILL.md is about 202 tokens. Licence: MIT.

Workflow steps

3 steps, taken from the first numbered list in SKILL.md.

  1. Discovers tests in tests/consensus/
  2. Executes spec tests to generate fixtures
  3. Outputs JSON fixtures to fixtures/consensus/

What it can do on your machine

Read from SKILL.md and the folder at commit 0b7d33e. 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:

    • uv
    • just

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

  • Network

    No URLs in SKILL.md. Its commands use uv, 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

Fill loads about 202 tokens when it runs. Until then it costs about 11 tokens; SKILL.md has 89 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~11
When it runs · the whole SKILL.md, loaded when a task matches
~202

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 leanEthereum/leanSpec at commit 0b7d33e, republished under its MIT licence (© leanEthereum). 89 words, ~202 tokens.

Download SKILL.mdSave it as .claude/skills/fill/SKILL.md (or your agent's skills folder).
name
fill
description
Generate consensus layer test fixtures

/fill - Generate Test Fixtures

Run the test filler to generate consensus layer test fixtures.

Default Usage

bash
uv run fill --fork=Lstar --clean -n auto

Options

Pass additional arguments after --:

  • /fill -- --scheme=prod - Use production signature scheme (slower)
  • /fill -- --fork=<other> - Generate for a different fork
  • /fill -- path/to/test.py - Generate fixtures for specific test file

What It Does

  1. Discovers tests in tests/consensus/
  2. Executes spec tests to generate fixtures
  3. Outputs JSON fixtures to fixtures/consensus/

The just fill-ci recipe wraps the same command for CI; contributors should invoke uv run fill directly so flags like --fork and --clean stay visible.

© leanEthereum, 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 .claude/skills/fill of leanEthereum/leanSpec.

Open the folder on GitHubat commit 0b7d33e

Compare with similar skills

Fill 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.

Fill compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Fill this skillleanEthereum/leanSpec143—~202Automated safety check: PassMIT
Fill Testsethereum/execution-specs1.2k—~793Automated safety check: PassCC0-1.0
Update Est Fixturesethereumjs/ethereumjs-monorepo2.8k—~3.3kAutomated safety check: PassNone
Jest Testing PatternsChrisWiles/claude-code-showcase6.1k7 repos~1.5kAutomated safety check: PassNone
Java SDK E2E Test with Replay Snapshotgithub/copilot-sdk11k—~1.8kAutomated safety check: PassMIT
source-mssql E2E Test Harnessairbytehq/airbyte22k—~4.4kAutomated safety check: PassCustom licence

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  • Fill Tests

    ethereum/execution-specs

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More from leanEthereum/leanSpec

All 9 skills in this repo

  • Audit

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    Read-only, multi-agent audit of the leanSpec codebase. An agent skill from leanEthereum/leanSpec.

    143 GitHub stars~2.5k tokensUpdated 1 mo ago
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  • Client Test

    leanEthereum/leanSpec

    Run leanSpec fixtures against a client implementation. An agent skill from leanEthereum/leanSpec.

    143 GitHub stars~594 tokensUpdated 1 mo ago
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  • Review

    leanEthereum/leanSpec

    Quick-reference checklist for code review conventions in leanSpec

    143 GitHub stars~468 tokensUpdated 1 mo ago
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  • Spec Diff

    leanEthereum/leanSpec

    Show what changed in leanSpec between devnet versions or HEAD

    143 GitHub stars~1.2k tokensUpdated 1 mo ago
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  • Workflows

    leanEthereum/leanSpec

    Common developer workflows, commands, and troubleshooting for leanSpec

    143 GitHub stars~496 tokensUpdated 1 mo ago
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  • Doc

    leanEthereum/leanSpec

    Document code in this repository.

    143 GitHub stars~1.9k tokensUpdated 1 mo ago
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Works with

Categories

Questions about Fill

How do I install Fill in Claude Code?

Run `npx skills add leanEthereum/leanSpec --skill fill -a claude-code`. Or copy the skill folder (.claude/skills/fill in leanEthereum/leanSpec) into .claude/skills/fill in your project. Claude Code loads it when a task matches its description.

How do I install Fill in Codex?

Run `npx skills add leanEthereum/leanSpec --skill fill -a codex`. Or copy the skill folder (.claude/skills/fill in leanEthereum/leanSpec) into .agents/skills/fill in your project. Codex loads it when a task matches its description.

Can I use Fill 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 leanEthereum/leanSpec --skill fill -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/fill, .gemini/skills/fill, .github/skills/fill and .opencode/skills/fill in your project.

What does Fill need to run?

Going by SKILL.md and its folder, Fill needs the command-line tools its instructions call (uv and just).

Does Fill access the network?

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

Is Fill 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 Fill use?

Fill 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 Fill use?

About 202 tokens (SKILL.md is roughly 808 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 Fill?

Skills that share tags, products or a category with Fill: Fill Tests (ethereum/execution-specs, 1.2k stars), Update Est Fixtures (ethereumjs/ethereumjs-monorepo, 2.8k stars), Jest Testing Patterns (ChrisWiles/claude-code-showcase, 6.1k stars) and Java SDK E2E Test with Replay Snapshot (github/copilot-sdk, 11k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Fill?

leanEthereum (a GitHub organization) maintains it in leanEthereum/leanSpec, which has 143 GitHub stars. The repository holds 9 skills in this directory. The repository was last updated on September 2, 2026.

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