> For the complete documentation index, see [llms.txt](https://engineering.umh.app/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://engineering.umh.app/engineering/development-process/how-to-build/coding-standards/code-quality/code-comments.md).

# Code comments

What a doc comment and an inline comment are for, in every language.

Owner: Jeremy

Every exported function, type and component has a doc comment. Inside the code, a comment is the last resort.

This page comes after [Abstractions](/engineering/development-process/how-to-build/coding-standards/code-quality/abstractions.md) and [Readability](/engineering/development-process/how-to-build/coding-standards/code-quality/readability.md). A comment holds what is left.

## Rules

* Every exported function, type and component has a doc comment in the form its language expects.
* We write an inline comment only for what the code cannot say after we [made it explain itself](/engineering/development-process/how-to-build/coding-standards/code-quality/readability.md#make-the-code-explain-itself).

## Doc comments

**A doc comment is for the person who uses the code.** It says what a function, type or component does. It does not repeat the name or the types.

The form depends on the language:

* Go: [Go: code comments](/engineering/development-process/how-to-build/coding-standards/languages/go/go-code-comments.md), our own page.
* TypeScript: the JSDoc rules in [Google's style guide](https://google.github.io/styleguide/tsguide.html#comments-documentation), which our [TypeScript](/engineering/development-process/how-to-build/coding-standards/languages/typescript.md) page follows.
* Svelte: [the Svelte docs on documenting components](https://svelte.dev/docs/svelte/faq#How-do-I-document-my-components).

## Inline comments

**An inline comment is for the person who changes the code.** It holds what is left after the code explains itself. [Readability](/engineering/development-process/how-to-build/coding-standards/code-quality/readability.md#make-the-code-explain-itself) describes how to get there.

**An inline comment sits next to the step it explains.** A long comment above a function that lists every step makes the reader hold the whole list in mind.

**An example often says more than a description.** A field for a message to the user can say: this is the message the frontend shows, for example "CPU limit reached".

**A field comment can name who reads the field.** A paragraph about a status field's wire format was replaced by one line: "this is read by the Management Console frontend and ProtocolConverterService.IsResourceLimited".

**Code that follows an outside format links to its documentation.** Code that parses the Linux cpuset format links to the kernel's documentation of that format. The comment then only says what we expect from the input.

## What goes elsewhere

**A comment describes the code as it is now.** Why the code has this shape belongs in the comment. How it got there belongs in the commit message, as [Readability](/engineering/development-process/how-to-build/coding-standards/code-quality/readability.md#give-context) describes.

**A comment that discloses a known defect links its bug ticket or** [**tech-debt ticket**](/engineering/development-process/how-to-build/tickets/tech-debt.md)**.** The ticket is where someone picks the defect up.


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