code-that-fits-in-your-head

Software engineering heuristics from Mark Seemann's book Code That Fits in Your Head (2021). Use when writing new code, reviewing code, refactoring, designing APIs, handling validation and invariants, writing unit tests, debugging defects, performing security review (STRIDE), or setting up a new code base. Covers decomposition (cyclomatic complexity, 80/24 rule, cohesion, fractal architecture), encapsulation (invariants, parse-don't-validate, Postel's law), outside-in TDD (walking skeleton, AAA, triangulation, devil's advocate), API design (affordance, poka-yoke, CQS), git/PR hygiene (50/72 commits, small commits, code review), feature flags, Strangler pattern, bisection debugging, logging with decorators, and STRIDE threat modelling. Not for language-specific syntax, framework tutorials, production incident response, or performance profiling.