Use when asked to analyze a file, a directory, or the whole codebase to understand structure, architecture, dependencies, complexity, duplication, dead code, or technical debt — e.g. "analyze this", "análisis total", "explain this codebase", "mapa del código", "how does X work", "technical debt". Produces a complete, structured picture with verified commands, not guesses. Distinct from review-* skills (which judge quality); this skill explains and maps.

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Use when asked to audit or harden security in this repo — e.g. "security audit", "auditoría de seguridad", "revisa la seguridad", "is this secure", "hardening", "vulnerabilities". Audits code, config, workflows, and secrets exposure. Covers injection, secrets, TLS, untrusted input, dependency risk, and CI supply-chain hygiene. Runs when the user asks about security, not just for code reviews.

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Use when writing, expanding, rewriting, or drafting any chapter (.mdx) or Go exercise for this book. Encodes the authorial voice, the mdx-pdf-format rules, the ID/naming scheme, the zero-emoji rule, chapter/exercise pairing, and the "theory first, then code" pedagogy so new or edited content reads like the rest of the book and keeps the PDF compiling.

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Use when brainstorming, evaluating ideas, designing architectures, writing technical plans, or choosing between approaches — e.g. "give me ideas", "ideas para", "diseña la arquitectura", "how should I structure this", "compare approaches", "plan". Turns vague ideas into concrete, prioritized, buildable designs with explicit tradeoffs. Use before writing code, not after.

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Use when proofreading, copy-editing, or verifying English in any docs/**/*.mdx chapter or code comment in this repo. Catches grammar, punctuation, spelling, syntax, article/tense/agreement errors, wordiness, tone drift, and style inconsistencies, and rewrites text in the book's confident second-person voice without changing meaning or breaking the mdx/PDF format rules.

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Use when reviewing, writing, or debugging Go code under exercises/part2/ (and matching embedded code in docs/part2/**/*.mdx). Thinks hard about correctness, idiomatic Go, error handling, resource cleanup, concurrency, and — crucially — what the tests would catch: edge cases, races, leaks, timeouts, and port conflicts. Knows the repo's module-mode quirk (GO111MODULE=off) and which dirs carry go.mod.

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