git:20260814.8461870 to git:20260910.1cac472

---

name: code-standards

description: Use when writing, modifying, reviewing, or refactoring code — any language or stack, application, infrastructure, or configuration. Also when asked to apply, audit, or clean up the code standards of a file or module.

---

# Code Standards

Code Standards governs how code is expressed — clarity, simplicity, safety, and

maintainability — not which architectural pattern should exist. Use the applicable

domain or pattern guidance to determine the design; use these standards to implement

that design clearly and safely.

## Iron Law

Write code so that its behavior, responsibility, and intent can be understood from

the implementation itself. Prefer code that explains itself over explanations

surrounding unclear code.

## Mental Model

A good implementation lets another engineer — or another agent — determine what

assumptions it relies on and where to look when behavior must change. Clarity

reduces the amount of inference required to safely modify the system.

## Rules

### 1. Make responsibility visible

Before adding code, identify the responsibility being implemented and the existing

pattern it belongs to; names, boundaries, and structure should reveal that

responsibility. Follow the local pattern when one exists — it settles the form of what

you write, never whether it was warranted, and matching what surrounds you is no

evidence that what surrounds you earned its place. A new abstraction or pattern should

exist because the problem requires it, not because the current implementation can be

made more elaborate.

### 2. Prefer the simplest complete implementation

Implement the behavior required by the current problem. Additional abstractions,

configuration, indirection, branches, or extensibility added for hypothetical future

cases increase the number of assumptions a reader must understand and the number of

places a future change can fail. Safety comes from making current assumptions and

boundaries explicit, not from anticipating every possible implementation.

### 3. Make behavior explicit

Important behavior should be visible in code rather than hidden behind unexpected

side effects, implicit state, or unrelated abstractions. Inputs, transformations,

state changes, and failure paths should be traceable from the implementation.

### 4. Keep changes local

A change should touch the smallest coherent surface that correctly implements the

behavior; a small blast radius makes it easier to reason about, verify, and revert.

### 5. Protect boundaries

Treat external input, configuration, network responses, persisted data, and other

trust boundaries explicitly. Validate where data enters a trusted part of the system

rather than spreading defensive assumptions throughout the implementation. Sensitive

values should not become source code, logs, error messages, or other persistent

output.

### 6. A comment is the exception, not the default

Default to no comment. Each one is optional and justified on its own: it earns its line

only by carrying a fact the code cannot state — why a non-obvious decision exists, an

invariant that must hold, an external constraint, a compatibility requirement, a

surprising consequence of changing the code. A comment that narrates the implementation

carries no such fact and leaves a second description to drift from the first. One

comment is not optional: the contract the caller reads, description or docstring, one

sentence saying what the unit promises.

Size a comment to its facts, never to the size of what it heads: one fact rarely needs

more than about two lines, and four chained facts are four entries in a dry list of

about a line each. Neither figure is a count to satisfy — padding one fact to two lines

and truncating a real chain to look short fail the same way.

that leaves a commented file carrying as much comment as it found owes an account of

why each line survived, whatever route it took to get there.

### 7. Comments are context, not evidence

When reading existing code, use comments as navigation and historical context. Verify

claims about behavior against the implementation, tests, configuration, or other

executable source of truth before relying on them. A stale comment should not

override what the system actually does: treating it as truth makes an agent reason

about behavior that no longer exists.

### 8. Route each fact to the declaration that owns it

Who reads a fact decides where it lives. A fact the caller needs goes in the slot that

A fact only a maintainer needs belongs to the declaration whose constraint produces it,

not to the line where the value happens to sit. Ask whose change would make it false:

if changing how the resource iterates falsifies the comment, the fact is the

resource's, and the map it consumes is merely where the value lives. The fact travels

up to that declaration's header, and bodies — argument lists, value maps, local blocks

— stay data a reader can scan with no prose in the way.

Never write a comment beside code on the same line. Whatever the column limit, the

margin left over fits a fragment, and a fragment of a why is a description: the form

manufactures the narration every other rule here exists to prevent.

When a declaration is long enough that its header leaves the target ambiguous, name the

field — "retention_policy is deliberately unlocked: locking is irreversible." Naming a

field of the declaration being read is a coordinate, not a pointer outward; reordering

cannot break what does not depend on position.

### 9. Verify behavioral changes

When behavior changes, verify the observable behavior rather than only the shape of

the implementation. Tests should protect meaningful behavior and invariants,

especially where a future refactor could accidentally change them.

## Traps

| Trap | Why it fails |

|------|--------------|

| Copying a nearby pattern without understanding its responsibility | Structural similarity can hide different assumptions and failure modes. |

## Anti-Patterns

### Clever compression

Code minimizes lines at the cost of making state changes, conditions, or data

transformations harder to see; behavior hidden behind convenience helpers makes the

code shorter while the actual control flow becomes harder to trace. Optimize for

understanding rather than line count.