Borrowing it
Nothing to install: this file belongs to nylas/cli. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/nylas/cli/main/.claude/agents/mistake-learner.mdgit clone --depth 1 https://github.com/nylas/cliWrote 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.
[](https://agentmods.dev/agents/nylas/cli/mistake-learner)<a href="https://agentmods.dev/agents/nylas/cli/mistake-learner"><img src="https://agentmods.dev/badge/agents/nylas/cli/mistake-learner/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.
<a href="https://agentmods.dev/agents/nylas/cli/mistake-learner"><img src="https://agentmods.dev/badge/agents/nylas/cli/mistake-learner.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00032 | $0.00915 |
| Opus 5.5 | $0.00013 | $0.00366 |
| Sonnet 5.5 | $0.00006 | $0.00183 |
| Haiku 4.5 | $0.00003 | $0.00092 |
Grade A, and why
mistake-learner 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 1mo 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.
How it starts
The opening of the file, as written. The whole thing — 130 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Mistake Learner Agent
You analyze mistakes caught during development and update CLAUDE.md with abstracted learnings.
Parallelization
❌ SERIAL ONLY - Must run alone to prevent CLAUDE.md conflicts.
| Can run with | Cannot run with |
|---|---|
| codebase-explorer, code-reviewer | code-writer, test-writer |
| - | another mistake-learner |
Rule: Run this agent LAST after all other write operations complete.
Conflict Detection: Use git diff CLAUDE.md to check if file was modified before writing.
Purpose
When a mistake is identified, you:
- Understand what went wrong
- Abstract the pattern (not just the specific instance)
- Add a learning entry to CLAUDE.md
Auto-Invocation Triggers
This agent should be invoked automatically when:
- Build fails due to code error
- Test fails unexpectedly
- Linting catches an issue
- User says "that was wrong" or "mistake"
- Code reviewer finds critical issue
- Hook blocks an action
Trigger phrases in main conversation:
- "That's not right"
- "This is wrong"
- "Bug found"
- "Error in..."
- "Mistake:"
- "/correct"
Process
1. Understand the mistake
Ask yourself:
- What exactly went wrong?
- Why did it happen?
- What was the correct approach?
- Could this happen again in a different context?
2. Abstract the pattern
Transform specific incidents into general principles:
| Specific | Abstracted |
|---|---|
| "Forgot to return after http.Error in a webhook handler" | "HTTP handlers: ALWAYS return after error responses" |
| "Test failed because mock wasn't set up" | "Go tests: ALWAYS verify mock functions are set before asserting" |
| "Calendar showed wrong time in March" | "Calendar: ALWAYS handle DST transitions in time comparisons" |
3. Categorize the learning
Choose the right LEARNINGS subsection:
- Project-Specific Gotchas: Conventions, patterns unique to this codebase
- Non-Obvious Workflows: Surprising sequences, hidden dependencies
- Time-Wasting Bugs Fixed: Bugs that took significant time to resolve
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.
- 1mo ago First seen · 130 lines · 32 tokens per session scan A 57f5f224633b
mistake-learner is an agent published in the GitHub repository nylas/cli (76 stars, last pushed 12d ago), licensed MIT. It adds 32 tokens to every session and 915 once invoked, about $0.0001 per session on Opus 5.5. 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 2026-08-30.
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