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Contributing to Tokei

Language Addition

Currently tokei generates languages from the languages.json file. JSON was decided to make it easy to add new languages, and change code structure without changing large data structures. Here we will go over the properties of a language in languages.json, through examples.

"JavaScript": {
      "line_comment": ["//"],
      "multi_line_comments": [["/*", "*/"]],
      "quotes": [["\\\"", "\\\""]],
      "quotes": [["\\\"", "\\\""], ["'", "'"], ["`", "`"]],
      "extensions": ["js", "mjs"]

Above is the JavaScript's definition. The first thing that needs to be defined is the key, the keys format should be same as Rust's enum style. As this key will be used in an enum for identifying the language. For a lot of language's this also works for showing the language when we print to the screen.

However there are some languages whose names don't work with the enum style. For example JSON is usually shown in all caps, but that doesn't fit in Rust's enum style. So we have an additional optional field called name, which defines how the language should look when displayed to the user.

"Json" {
    "name": "JSON",

For defining comments has a few properties: firstly is the most commonly used line_comment property which defines single line comments. Comments which don't continue onto the next line.

let x = 5; // default x position
let y = 0; // default y position

The line_comment property expects an array of strings, as some languages have multiple syntaxes for defining a single line comment. For example PHP allows both # and // as comments.

"Php": {
    "line_comment": [

For defining comments that also have a ending syntax, there is the multi_line property.

let x = /* There is a reason
    for this comment I swear */

The verbatim_quotes property expects an array of strings, as some languages have multiple syntaxes for defining verbatim strings. A verbatim string in the context of Tokei is a string literal that can have unescaped "s. For example CSharp

"CSharp": {
  "verbatim_quotes": [
const string BasePath = @"C:\";

Some languages have a single, standard filename with no extension like Makefile or Dockerfile. These can be defined with the filenames property:


Filenames should be all-lowercase, whether or not the filename typically has capital letters included.

Note that filenames will override extensions with the following definition a file named CMakeLists.txt will be detected as a CMake file, not a Text file.

    "filenames": [


A test file is required with language additions. The file should contain every variant comments and quotes, as well as a comment at the top of the file containing the manually verified lines, code, comments, blanks in the following format.

NUM lines NUM code NUM comments NUM blanks


//! 39 lines 32 code 2 comments 5 blanks

The comment should use the syntax of the language you're testing. A good example of a test file is tests/data/

// 41 lines 33 code 3 comments 5 blanks

/* /**/ */
fn main() {
    let start = r##"/*\"
    // comment
    loop {
        if x.len() >= 2 && x[0] == '*' && x[1] == '/' { // found the */

fn foo<'a, 'b>(name: &'b str) {
    let this_ends = "a \"test/*.";
    let this_does_not = /* a /* nested */ comment " */
        "*/another /*test

fn foobar() {
    let does_not_start = // "
        "until here,
        test"; // a quote: "
    let also_doesnt_start = /* " */
        "until here,
        test"; // another quote: "

fn foo() {
    let a = 4; // /*
    let b = 5;
    let c = 6; // */

Bug Reports

Please include the error message, and a minimum working example including the file, or file structure.

This file crashes the program.