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Agent skill

Spec Diff

by leanEthereum in leanEthereum/leanSpec

Show what changed in leanSpec between devnet versions or HEAD

MITAuto-check passedDevelopment

Install Spec Diff

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

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

GitHub CLI
$ gh skill install leanEthereum/leanSpec spec-diff --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/spec-diff .claude/skills/spec-diff && 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
spec-diff
GitHub stars
143
Token cost
~1.2k tokens
SKILL.md length
508 words
Files
1
Skills in repo
9
Repo updated
First seen
Licence
MIT

At a glance

Show what changed in leanSpec between devnet versions or HEAD

  • Works in 5 steps: Resolve version commits → Get changed files → Analyze spec changes → …
  • Development work in your project
  • SKILL.md covers Usage and Steps
  • Calls git

What it does

Spec Diff is an agent skill from leanEthereum/leanSpec. Show what changed in leanSpec between devnet versions or HEAD

Its SKILL.md is about 1.2k 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 Development. It works with Ethereum. The repository describes itself as: Lean Ethereum protocol specifications and test vector generation framework. The licence is MIT.

When your agent uses it

  • Development work in your project

Example prompts

  • “/spec-diff”

Workflow steps

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

  1. Resolve version commits
  2. Get changed files
  3. Analyze spec changes
  4. Analyze test vector changes
  5. Output report

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:

    • git

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

  • Network

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

Spec Diff loads about 1.2k tokens when it runs. Until then it costs about 18 tokens; SKILL.md has 508 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~18
When it runs · the whole SKILL.md, loaded when a task matches
~1.2k

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 leanEthereum/leanSpec at commit 0b7d33e, republished under its MIT licence (© leanEthereum). 508 words, ~1,212 tokens.

Download SKILL.mdSave it as .claude/skills/spec-diff/SKILL.md (or your agent's skills folder).
name
spec-diff
description
Show what changed in leanSpec between devnet versions or HEAD

/spec-diff - Spec Changelog Between Versions

Show what changed in the spec code (src/lean_spec/) and consensus test vectors (tests/consensus/) between two devnet versions (or HEAD).

Scope: Protocol-level spec types, functions, containers, forkchoice logic, and the test fixtures that generate cross-client test vectors.

Excluded: Test framework infrastructure (packages/testing/, consensus_testing/), unit tests (tests/), interop tests (tests/interop/), documentation (docs/), CI/tooling configs, and the node implementation layer (networking, sync, storage, node runner).

Usage

  • /spec-diff devnet3 - Changes from devnet 3 to HEAD
  • /spec-diff devnet2 devnet3 - Changes from devnet 2 to devnet 3
  • /spec-diff devnet0 devnet3 - Full changelog across multiple devnets

Steps

1. Resolve version commits

Look up commit hashes from VERSIONS.md in the repo root. It contains a table mapping version names (e.g. "Devnet 3") to commit hashes.

Parse the argument(s):

  • If one argument: compare that version → HEAD
  • If two arguments: compare first → second
  • Match case-insensitively and flexibly (e.g. devnet3, Devnet 3, d3 should all resolve to the same entry)

If a version is not found in VERSIONS.md, report the available versions and abort.

2. Get changed files

Run both commands:

bash
git diff --name-only <from-commit> <to-commit> -- src/lean_spec/
git diff --name-only <from-commit> <to-commit> -- tests/consensus/

Filter to .py files only.

3. Analyze spec changes

For each changed spec file (src/lean_spec/), run:

bash
git diff <from-commit> <to-commit> -- <file>

Categorize each item as:

  • New - functions/types/modules that didn't exist in the from-version
  • Modified - functions/types whose signature or body changed (includes renames)
  • Removed - functions/types that were deleted

For modified items, briefly describe what changed (e.g. "added deadline parameter", "changed return type from bool to Optional[bool]").

Detecting renames: A rename+change appears in the diff as a removal in one place and an addition in another. Before classifying something as [Removed] + [New], check whether the removed item has a corresponding new item with a similar name, similar parameters, or similar objective. If so, report it as a single [Modified] entry: old_name() → renamed to new_name(), with a description of what else changed. Common rename patterns: prefix/suffix changes (gossip_ → attestation_), class extraction (function → Class.method), split (one_func → two_funcs).

Show full SKILL.md (195 more words)Show less
4. Analyze test vector changes

For each changed consensus test file (tests/consensus/), run:

bash
git diff <from-commit> <to-commit> -- <file>

Summarize changes to test vectors grouped by test category (fork choice, SSZ, signature verification, etc.). Focus on:

  • New test cases added
  • Tests whose scenarios changed (e.g. "blocks now carry explicit attestations instead of relying on auto-collection")
  • Tests removed
  • Behavioral changes in what's being tested (e.g. "fork weight now based on attestations not block count")
5. Output report

Group changes by component (logical area of the spec), not by file path. Within each component, prefix each item with [New], [Modified], or [Removed].

After the spec component sections, include a Test Vectors section covering changes to consensus test fixtures (tests/consensus/).

markdown
## Spec changes: Devnet 3 → HEAD

### Block Envelope

- [New] `SignedBlock` — replaces `SignedBlockWithAttestation`
- [Removed] `BlockWithAttestation` — no longer needed

### State Transition

- [Modified] `State` — added `deposit_index` field (Uint64)

### Test Vectors

**Fork Choice** (5 files, +770 -407 lines)
- [Modified] Tests now use explicit attestations — weight from attestations not block count
- [Removed] `test_auto_collect_proposer_attestations` — auto-collection removed

**SSZ Containers** (2 files)
- [Modified] `Validator` tests — dual pubkeys

### Summary
- X spec files, Z test files changed
- Brief description of core design changes

Guidelines:

  • Group spec changes by logical component (e.g. "Block Envelope", "Validator Model", "Aggregation", "Forkchoice Store"), not by file path.
  • Each item is a bullet prefixed with [New], [Modified], or [Removed].
  • The Test Vectors section groups by test category (fork choice, SSZ, signature verification, state transition, etc.) with file counts and line stats.
  • Keep descriptions concise. The goal is to give implementation teams a clear picture of what they need to update, not a line-by-line diff.
  • End with a Summary section highlighting core design changes.

© 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/spec-diff of leanEthereum/leanSpec.

Open the folder on GitHubat commit 0b7d33e

Compare with similar skills

Spec Diff 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.

Spec Diff compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Spec Diff this skillleanEthereum/leanSpec143—~1.2kAutomated safety check: PassMIT
Wagmi Feature Developmentwevm/wagmi6.8k—~3.8kAutomated safety check: PassMIT
Release Roundethereumjs/ethereumjs-monorepo2.8k—~2kAutomated safety check: PassNone
Update Est Fixturesethereumjs/ethereumjs-monorepo2.8k—~3.3kAutomated safety check: PassNone
Starknet JSstarknet-io/starknet.js1.3k—~1.2kAutomated safety check: PassMIT
Lean Reviewgeanlabs/gean177—~1.5kAutomated safety check: PassNone

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  • Workflows

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    Common developer workflows, commands, and troubleshooting for leanSpec

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  • Doc

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Works with

Categories

Questions about Spec Diff

What does Spec Diff do?

Show what changed in leanSpec between devnet versions or HEAD. Spec Diff is an agent skill from leanEthereum/leanSpec.

When should I use Spec Diff?

Spec Diff fits situations like: development work in your project.

How do I install Spec Diff in Claude Code?

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

How do I install Spec Diff in Codex?

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

Can I use Spec Diff 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 spec-diff -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/spec-diff, .gemini/skills/spec-diff, .github/skills/spec-diff and .opencode/skills/spec-diff in your project.

What does Spec Diff need to run?

Going by SKILL.md and its folder, Spec Diff needs the command-line tools its instructions call (git).

Does Spec Diff access the network?

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

Is Spec Diff 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 Spec Diff use?

Spec Diff 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 Spec Diff use?

About 1.2k tokens (SKILL.md is roughly 4.8k 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 Spec Diff?

Skills that share tags, products or a category with Spec Diff: Wagmi Feature Development (wevm/wagmi, 6.8k stars), Release Round (ethereumjs/ethereumjs-monorepo, 2.8k stars), Update Est Fixtures (ethereumjs/ethereumjs-monorepo, 2.8k stars) and Starknet JS (starknet-io/starknet.js, 1.3k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Spec Diff?

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.