Andrej Karpathy: "90% of Claude's mistakes come from missing context, not a weak model."
41% mistake rate without a CLAUDE.md. 11% with the 4-rule baseline. 3% with the 12-rule version below
here are the 12 rules senior engineers settled on:
1. think before coding: state assumptions, don't guess. the model can't read your mind, stop hoping it will
2. simplicity first: minimum code, no speculative abstractions. the moment you let Claude add "for future flexibility," you've added 200 lines you'll delete next quarter
3. surgical changes: touch only what you must. don't let it improve adjacent code, that's how PRs blow up
4. goal-driven execution: define success criteria upfront, loop until verified. without them Claude either loops forever or stops too early
5. use the model only for judgment calls: classification, drafting, summarization, extraction. NOT routing, retries, status-code handling, deterministic transforms. if code can answer, code answers
6. token budgets are not advisory: per-task 4000, per-session 30000. by message 40 of a long debug, Claude is re-suggesting fixes you rejected at message 5
7. surface conflicts, don't average them: two patterns in the codebase? pick one. Claude blending them is how errors get swallowed twice
8. read before you write: read exports, callers, shared utilities. Claude will happily add a duplicate function next to an identical one it never read
9. tests verify intent, not just behavior: a test that can't fail when business logic changes is wrong. all 12 of Claude's tests can pass while the function returns a constant
10. checkpoint every significant step: Claude finished steps 5 and 6 on top of a broken state from step 4. nobody noticed for an hour
11. match the codebase conventions: class components? don't fork to hooks silently. testing patterns assumed componentDidMount, hooks broke them without surfacing
12. fail loud: "completed successfully" with 14% of records silently skipped is the worst class of bug. surface uncertainty, don't hide it
what actually compounds instead of the next framework:
- the CLAUDE.md file as institutional memory across sessions
- eval-driven changes, not vibe-driven
- checkpoints over speed
- explicit conflicts over silent blending
- discipline over framework, every time
- one repo, one rules file, no exceptions
be a few rules ahead of AI twitter before this becomes mass-opinion
study this
VERCEL GOT HACKED
ShinyHunters - the group behind the Ticketmaster breach - is selling Vercel's internal database for $2M on BreachForums
here's why every developer should care:
- they have NPM tokens and GitHub tokens
- Vercel owns Next.js - 6 million weekly downloads
- one malicious push = global supply chain attack
- Vercel confirmed the breach today, April 19
- they literally DMed the hackers on Telegram asking them to stop
rotate your env variables RIGHT NOW
We’ve identified a security incident that involved unauthorized access to certain internal Vercel systems, impacting a limited subset of customers. Please see our security bulletin:
https://t.co/0S939n3qHC
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