lessons

lessons is a command for coding agents from fusengine/agents. It costs 26 tokens per session (550 once invoked), scanned A, original, MIT.

A project command for reading and recording lessons in MEMORY/LESSON.md, a file of short notes about mistakes the project should not repeat.

In plain words
What is it for?
Use it to view existing project lessons or append a concise note about what went wrong and what to do differently next time.
Why use it?
It keeps useful lessons available across future sessions and helps the team remember past problems without rereading full post-mortems.

Command

Part of the fuse-lessons plugin — 2 commands, 1 agent 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 commands/fusengine/agents/lessons
Clone the repo
git clone --depth 1 https://github.com/fusengine/agents

Or install fuse-lessons, the plugin that ships this one along with the rest of its 2 commands, 1 agent.

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 lessons

README.md
[![agentmods](https://agentmods.dev/badge/commands/fusengine/agents/lessons.svg)](https://agentmods.dev/commands/fusengine/agents/lessons)
Your own site
<a href="https://agentmods.dev/commands/fusengine/agents/lessons"><img src="https://agentmods.dev/badge/commands/fusengine/agents/lessons.svg" alt="Measured on agentmods" height="20"></a>
Per session 26 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 550 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 5.1 $0.00026 $0.00550
Opus 5 $0.00013 $0.00275
Sonnet 5 $0.00005 $0.00110
Haiku 4.5 $0.00003 $0.00055

Measured 2d ago against content hash 557d62397709, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-05, from the pricing page.

Security

Grade A, and why

lessons 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.

plugins/fuse-lessons/commands/lessons.md · 47 lines

How it starts

The opening of the file, as written. The whole thing — 47 lines — stays where its author put it; the contents beside it link to each section on GitHub.

/lessons

Manage the project's lessons memory — a MEMORY/LESSON.md file committed at the project root. It records compact post-mortems so the same mistake is never reproduced twice.

Architecture

  • MEMORY/LESSON.md — the committed list of lessons. One lesson per line, newest at the bottom. This is the file you read and append to.
  • MEMORY/state.json — the throttle counter (last-reminder / last-write timestamps). It is gitignored and managed by the hooks; never edit it by hand.

The fuse-lessons hooks force-read MEMORY/LESSON.md at every session and sub-agent start, so anything written here is automatically reloaded into context.

View existing lessons

Read MEMORY/LESSON.md at the project root (create it if absent). Each line is one lesson, newest at the bottom.

Add a lesson

Append one line in this exact compact format:

- [YYYY-MM-DD HH:MM] <what went wrong> → <what to do instead>

Rules:

  • One lesson per line. Keep it short — a single actionable sentence.
  • Timestamp uses the current local date and time in YYYY-MM-DD HH:MM. The Stop hook injects the exact stamp to use — copy it verbatim.
  • Left of : the concrete failure (what broke, what was wrong).
  • Right of : the corrective action (what to do next time).
  • No paragraphs, no code blocks — just the bullet line.

Example

- [2026-06-20 11:02] Added "hooks": "./hooks/hooks.json" string in marketplace entry → never set a hooks field in marketplace.json; hooks auto-load by convention from hooks/hooks.json

Throttle

The Stop hook reminds you to capture a lesson at most once every 5 minutes by default. Override with the FUSE_LESSONS_THROTTLE_MIN environment variable (minutes). Writing to MEMORY/LESSON.md resets the throttle automatically via the PostToolUse hook (it updates MEMORY/state.json).

After appending, mention that the lesson will be force-read on the next session/sub-agent start, and that MEMORY/LESSON.md should be committed with the change so the whole team inherits it.

Read the full file on GitHub · 47 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. 2d ago First seen · 47 lines · 26 tokens per session scan A 557d62397709

Subscribe to this mod's changes

lessons is a command published in the GitHub repository fusengine/agents (25 stars, last pushed today), licensed MIT. It adds 26 tokens to every session and 550 once invoked, about $0.0001 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 2026-09-03.