lesson-learned

A code-review guide that examines recent changes in a Git repository, the system that records code history, and turns them into software-engineering lessons.

In plain words
What is it for?
Use it to reflect on a feature branch, recent commits, one commit, or uncommitted changes and extract practical lessons from the code.
Why use it?
It helps developers understand what their own changes demonstrate instead of receiving a general lecture. It also highlights possible mistakes or patterns worth improving.

Skill for Claude CodeCodex

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/softaworks/agent-toolkit/lesson-learned
Any agent
npx skills add softaworks/agent-toolkit --skill lesson-learned
Clone the repo
git clone --depth 1 https://github.com/softaworks/agent-toolkit

Made for: Claude Code, Codex.

Per session 64 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,097 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin 100% copy Near-identical to another mod 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 $0.00064 $0.01097
Opus 5 $0.00032 $0.00549
Sonnet 5 $0.00013 $0.00219
Haiku 4.5 $0.00006 $0.00110

Measured 2d ago against content hash f2ee51f30ea8, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

lesson-learned 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 2d 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.

Origin

This is a copy

100% identical to lesson-learned — 0 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

skills/lesson-learned/SKILL.md · 106 lines

How it starts

The opening of the file, as written. The whole thing — 106 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Lesson Learned

Extract specific, grounded software engineering lessons from actual code changes. Not a lecture -- a mirror. Show the user what their code already demonstrates.

Before You Begin

Load the principles reference first.

  1. Read references/se-principles.md to have the principle catalog available
  2. Optionally read references/anti-patterns.md if you suspect the changes include areas for improvement
  3. Determine the scope of analysis (see Phase 1)

Do not proceed until you've loaded at least se-principles.md.

Phase 1: Determine Scope

Ask the user or infer from context what to analyze.

Scope Git Commands When to Use
Feature branch git log main..HEAD --oneline + git diff main...HEAD User is on a non-main branch (default)
Last N commits git log --oneline -N + git diff HEAD~N..HEAD User specifies a range, or on main (default N=5)
Specific commit git show <sha> User references a specific commit
Working changes git diff + git diff --cached User says "what about these changes?" before committing

Default behavior:

  • If on a feature branch: analyze branch commits vs main
  • If on main: analyze the last 5 commits
  • If the user provides a different scope, use that

Phase 2: Gather Changes

  1. Run git log with the determined scope to get the commit list and messages
  2. Run git diff for the full diff of the scope
  3. If the diff is large (>500 lines), use git diff --stat first, then selectively read the top 3-5 most-changed files
  4. Read commit messages carefully -- they contain intent that raw diffs miss
  5. Only read changed files. Do not read the entire repo.

Phase 3: Analyze

Identify the dominant pattern -- the single most instructive thing about these changes.

Look for:

  • Structural decisions -- How was the code organized? Why those boundaries?
  • Trade-offs made -- What was gained vs. sacrificed? (readability vs. performance, DRY vs. clarity, speed vs. correctness)
  • Problems solved -- What was the before/after? What made the "after" better?
  • Missed opportunities -- Where could the code improve? (present gently as "next time, consider...")

Read the full file on GitHub · 106 lines

Files

What ships with it

3 files 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. 2d ago First seen · 106 lines · 64 tokens per session scan A f2ee51f30ea8

Subscribe to this mod's changes

lesson-learned is a skill published in the GitHub repository softaworks/agent-toolkit (2,413 stars, last pushed 6mo ago), licensed MIT. It adds 64 tokens to every session and 1,097 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. It is 100% identical to lesson-learned, differing in 0 lines, and is treated as a copy.

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