Code needs enough documentation for someone to use its public behavior safely and to understand important decisions that are not obvious from the code. There is no useful universal quota for comment lines or documentation pages. Write for the questions a caller, new user, operator, or maintainer cannot answer by reading clear names, types, tests, and structure.
How do you decide what needs documenting?
For each sentence you might add, ask: What could a new caller or maintainer misunderstand if this sentence were absent? Keep it if it answers a consequential question the code does not answer; remove or rewrite it if it merely narrates an obvious line or no longer matches behavior.
- Make the obvious clear in the code. Specific names and straightforward control flow often communicate more reliably than comments that repeat them.
- Document what cannot be inferred. Explain a non-obvious reason, constraint, edge case, or rule that someone could break by changing the code.
- Scale detail to risk. A small private script may need clear names and a short usage note; a public library, service, or safety-sensitive subsystem needs more explicit guidance because others depend on its behavior.
- Keep explanations true. A stale comment is worse than no comment when it leads a reader to trust behavior the code no longer has.
No source establishes a reliable universal number of comments, words, or documentation pages per codebase. A 2019 Google-published mapping study reviewed 21 prior works and organized 34 weighted recommendations across five dimensions; those figures describe the study, not a target amount for a project. The study abstract.
What belongs in a comment, an API reference, or a guide?
Put information where the person who needs it is most likely to look. Comments, API references, READMEs, task guides, and design records serve different readers; they are not a checklist of files every project must create.
#1 Best Overall
| Form | Reader’s question | Include | Avoid |
|---|---|---|---|
| Names and code structure | What is happening here? | Specific names, clear control flow, understandable abstractions | Generic names that force readers to hunt for explanations |
| Inline comment | Why is this choice unusual? | Rationale, constraints, non-obvious edge cases, domain context | Narration of an obvious statement or commentary duplicated by a name |
| API reference | How do I call this, and what does it promise? | Purpose, behavior, parameter and return meanings, errors, defaults, prerequisites, pitfalls | A vague summary that merely restates the method name |
| README | What is this package, and where do I begin? | Purpose, status, contacts, a first use or command, links to fuller documentation | A duplicate of an already maintained guide |
| Tutorial or operational guide | How do I complete this task? | Ordered steps, examples, setup, tests, debugging, release instructions | A long-lived procedure hidden in an incidental code comment |
| Design record | Why was this approach chosen? | Decision rationale and alternatives considered | Presenting an old proposal as the current user guide |
Google’s Documentation Best Practices describes inline comments as information the code itself cannot contain, such as why the code is there. It distinguishes that maintainer context from API documentation aimed at callers.
What should an inline comment explain?
Use inline comments for the missing context around an implementation: why an unusual choice exists, which constraint it satisfies, or what future changes must preserve. This matters particularly for business rules, security checks, performance trade-offs, and subtle language behavior.
Google’s Go Style Guide puts the principle succinctly: “It is often better for comments to explain why something is done, not what the code is doing.” Before adding one, consider:
- Would a good name and the surrounding code already make the behavior clear?
- Could someone make a real mistake without knowing this reason, constraint, or edge case?
- Is this caller-facing behavior, or implementation rationale meant for maintainers?
- Will the comment remain accurate as the code changes? Could a test, name, type, or simpler implementation express the invariant more reliably?
Comments do not have to be long to be useful. If a simple, stable operation is fully clear from its name and signature, a short description may be enough. Add detail when callers face a consequential choice or behavior is not obvious.
What should public API documentation cover?
A signature shows types, but often not what those types mean in practice. Document the contract callers rely on, especially anything they cannot safely guess:
- What each parameter means and which values are accepted.
- What the return value represents, including meaningful empty or error results.
- Whether the operation can throw, return an error, or have side effects.
- Required permissions, state, or other prerequisites.
- Defaults and what each meaningful option changes.
- Restrictions, common pitfalls, and related methods.
- A minimal example when it makes the first successful use easier to understand.
Google’s API reference guide recommends documenting public classes, interfaces, structs, constants, fields, enums, typedefs, and methods, including method parameters, returns, and exceptions. It advises beginning class documentation with its purpose and method documentation with the action, then adding relevant rationale, prerequisites, exceptions, or related APIs.
Rank #3
For .NET, Microsoft notes that triple-slash comments become public Learn documentation and appear in IntelliSense. Its contributor guidance calls for comments that are complete, correct, contextual, and polished. A caller should not have to inspect the implementation just to learn what an option means or what an error indicates.
What belongs in a README or a fuller guide?
A package README should orient someone arriving at that directory for the first time: what it is for, its status, whom to contact, and how to begin. Google’s README guidance also recommends linking to relevant documentation.
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Clear out junk files and repair common Windows errorsFree Scan →Scan for outdated or missing drivers - takes under a minuteDriver Scan →Move procedures that users or operators need to repeat into a guide: getting started, running tests, debugging output, or releasing a binary. If an authoritative guide already exists, link to it rather than maintaining a competing copy. Keep design records for the reasons and alternatives behind an implementation, but do not let a completed proposal masquerade as instructions for using the current system. These distinctions follow Google’s documentation best-practices guidance.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.When are examples and tests worth adding?
Add an example when it answers a real usage question: perhaps an API has several ways to be called, or a first successful task is otherwise hard to infer. Google’s API reference guidance suggests a short example near the top of a unique API page, while acknowledging that the advice may not fit every language or API.
Tests can verify that documented behavior remains consistent with executable expectations. Google’s best-practices guide notes that testing documented method behavior is often reasonable. Tests do not, by themselves, tell a maintainer why an unusual decision exists; use an explanation for that context.
The 2019 mapping study’s abstract reports that usage details—including snippets, tutorials, and reference documents—were generally weighted as helpful, alongside design rationale and presentation. Its scope was 21 prior works and a taxonomy of five dimensions and 34 recommendations, not an experiment proving that every API needs every format. Read the study abstract.
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How should a team choose the right amount?
For each piece of information, weigh who needs it, what kind of knowledge it conveys, where that reader will look, how closely it changes with the source, and the cost of guessing wrong. An API contract belongs where callers can find it; a setup sequence belongs in a guide; a fragile implementation rationale belongs near the code it protects. The higher the harm from misunderstanding, the more explicit and discoverable the explanation should be.
Then review documentation as part of code maintenance: check that comments still match behavior, that guides point to the current workflow, and that duplicated explanations have not diverged. Research on developer discussions has described confusion around varied comment conventions and incomplete style-guide coverage, but it does not establish one universally best convention or a quantitative documentation target. The study abstract.
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