Engineering discipline for agents: ground before coding, no silent error swallows, one source of truth, verify before claiming done
Skill Claude CodeCodex
Part of principal-engineer
Use when about to add, update, vet, or remove a dependency - a package, library, SDK, GitHub action, base image, or vendored code - or when a project's dependency posture needs declaring. Encodes the exhaust-what-you-have ladder, the vetting questions, and pin-and-prove updating. Use even for a tiny utility package…
Skill Claude CodeCodex
Part of principal-engineer
Use when starting any non-trivial change, investigating a bug, or working in unfamiliar code - before the first line is written. Also use for pure investigation with no change planned yet - "dig into this", "figure out why", "sometimes the export is empty", intermittent errors after a deploy. Encodes the ground-first…
Skill Claude CodeCodex
Part of principal-engineer
Use when a change crosses module boundaries, adds a dependency direction between modules, touches a critical path, or conflicts with a stated principle - and when writing or updating architecture principles themselves. Encodes structural invariants as named, enforced contracts: statement, rationale, guard. Use…
Skill Claude CodeCodex
Part of principal-engineer
Use when writing or touching any error path, catch block, fallback, default value, retry, or degraded mode - in any language, any repo. Encodes the no-silent-swallows contract and the fail-loud discipline. Use whenever an exception is about to be caught, a null is about to get a default, or a failure could pass…
Skill Claude CodeCodex
Part of principal-engineer
Use when adding data, config, state, constants, an enum-like string, a cache, or anything that could exist in two places - or when two sources already disagree. Encodes the one-fact-one-source doctrine for code and data: derive rather than store, extend the owner, absorb duplicates. Use at the moment copying a value…
Skill Claude CodeCodex
Part of principal-engineer
Use when an action touches live systems, shared state, or things that do not come back - deleting, overwriting, restarting, killing processes, editing shared config, handling secrets, or working beside concurrent sessions. Encodes the destructive-op guards, secrets hygiene, and concurrent-session safety. Use before…
Skill Claude CodeCodex
Part of principal-engineer
Use when doing any non-trivial engineering work - implementing, debugging, refactoring, configuring, operating, or investigating why a system misbehaves - or any change where being wrong has a cost. Encodes the evidence-over-theory discipline, the hard safety rules, and the pre-change checkpoint. Use whenever code…
Skill Claude CodeCodex
Part of principal-engineer
Use when deciding how big a fix should be, when scope is drifting mid-task, when a plan is being quietly trimmed to fit, or when "while you're at it" appears in any form. Encodes size-to-trigger, decompose-not-descope, and drive-to-completion. Use whenever the work is about to grow past its cause or shrink below its…
Skill Claude CodeCodex
Part of principal-engineer
Use when deciding what tests a change needs - a feature, a bug fix, a refactor, any behavior change - or when reviewing whether a diff's tests are sufficient. Encodes tests-change-with-behavior, the bug-regression pattern, and assertion discrimination. Use whenever behavior changes and the test diff is empty…
Skill Claude CodeCodex
Part of principal-engineer
Use when about to say "done", "fixed", "passing", or "shipped" - or when reporting the outcome of any change. Encodes verification as the definition of done: drive the change at its surface, run the verify command, report faithfully, distrust green suites, own failing gates. Use before every completion claim, even…
Skill Claude CodeCodex
Part of principal-engineer
Use when writing or refactoring unit tests - a new test file, added cases, a flaky test, an unreadable one. Encodes behavior-first testing: one behavior per test, names that state the claim, deterministic setup, mocks only at boundaries you do not own. Use whenever a test is being written, even a quick one, and…
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