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Tool to generate documentation for Nix library functions [maintainer=@infinisil]


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This tool is used to generate reference documentation for Nix library functions defined in Nixpkgs' lib.

Check out this example of documentation generated for the lib/strings.nix file.

It uses rnix to parse Nix source files, which are then transformed into a CommonMark (with some syntax extensions) representation of the function set.

Comment format

This tool implements a subset of the doc-comment standard specified in RFC-145/doc-comments. But, it is currently limited to generating documentation for statically analysable attribute paths only. In the future, it could be the role of a Nix interpreter to obtain the values to be documented and their doc-comments.

It is important to start doc-comments with the additional asterisk (*) -> /** which renders as a doc-comment.

The content of the doc-comment should conform to the Commonmark specification.


The following is an example of markdown documentation for new and current users of nixdoc.

Sidenote: Indentation is automatically detected and should be consistent across the content.

If you are used to multiline-strings ('') in nix this should be intuitive to follow.

    This function adds two numbers

    # Example

    add 4 5

    # Type

    add :: Number -> Number -> Number

    # Arguments

    : The first number
    : The second number
  add = a: b: a + b;

Note: Within nixpkgs the convention of using definition-lists for documenting arguments has been established.

Custom nixdoc format (Legacy)

You should consider migrating to the newer format described above.

See Migration guide.

Comment format (legacy)

Identifiers are included in the documentation if they have a preceding comment in multiline syntax /* something */. You should consider migrating to the new format described above.

Two special line beginnings are recognized:

  • Example: Everything following this line will be assumed to be a verbatim usage example.
  • Type: This line will be interpreted as a faux-type signature.

These will result in appropriate elements being inserted into the output.

Function arguments (legacy)

Function arguments can be documented by prefixing them with a comment:

/* This function does the thing a number of times. */
myFunction =
    # The thing to do
    # How many times to do it
    n: doNTimes n thing

Caveats & TODOs

Please check the issues page.