BitDownToc adds a table of contents (TOC) to your Markdown files, either online or from the command line. It supports Gitlab and GitHub styles, and can generate anchors to comply with Bitbucket Server (and its lack of proper markdown support using the generic profile), dev.to, hashnode, and more!

Thanks to small comments (in HTML or liquid tags), it can also detect previously generated TOC, so you can run it every time you change your README without worries. In other words, it is idempotent 🤩.

It supports English, French, and most Latin languages, but not Cyrillic or Chinese!

TOC (generated by this tool, duh, using the github profile):

• Usage
  • Online
  • From the command line
  • About native executables
• TOC flavors (profiles)
  • Built-in profiles
  • Other platforms
  • Still not fitting your use case?
• TOC placement
• About the code
  • Motivation
  • Kotlin all the way!
  • Build and run
• Contributing
• About the license

Go to https://bitdowntoc.derlin.ch !

Having homebrew? Install bitdowntoc with:

brew install derlin/bitdowntoc/bitdowntoc

Otherwise, the JVM jar can be found in the releases. If you want the latest version, check the nightly release.

Native executables for Linux, Mac and Windows are available for releases only. See About native executables for more info.

Once installed, run:

# Generic, e.g. BitBucket Server
bitdowntoc readme.md --inplace
# GitLab
bitdowntoc -p gitlab readme.md --inplace # or
bitdowntoc --no-anchors readme.md --inplace
# GitHub
bitdowntoc -p github readme.md --inplace # or
bitdowntoc --no-anchors --no-concat-spaces readme.md --inplace
# DevTo
bitdowntoc -p devto
# Hashnode
bitdowntoc -p hashnode

# Piping from stdin
cat README.md | bitdowntoc

NOTE: if you are downloaded the jar, replace bitdowntoc above with java -jar bitdowntoc-jvm-*.jar. If you installed the native executable manually, replace bitdowntoc above with <path/to/executable>.

The tool will output the transformed file depending on the following options (mutually exclusive):

• default: output to stdout;
• -i/--inplace: replace input file (incompatible with reading from stdin);
• -o/--output: output to the specified file.

IMPORTANT: do not use bash redirects with the same file (input = output), it won't work as you expect!

If you have a doubt, run BitDownToc with -h or --help:

Usage: bitdowntoc [<options>] [<path>]

Options:
  --version                                Show version and exit
  --indent-chars=<text>                    Characters used for indenting the toc (default: '-*+')
  --indent-spaces=<int>                    Number of spaces per indentation level for indenting the toc (default: 3)
  --concat-spaces / --no-concat-spaces     Whether to trim heading spaces in generated links (foo-bar) or not
                                           (foo----bar) (default: true)
  --anchors-prefix=<text>                  Prefix added to all anchors and TOC links (e.g. 'heading-') (default: '')
  --anchors / --no-anchors                 Whether to generate anchors below headings (e.g. BitBucket Server) (default:
                                           true)
  --anchors-algo=(DEFAULT|DEVTO|HASHNODE)  How handle special chars, links, etc. in titles before generating anchor
                                           links (default: DEFAULT)
  --comment-style=(HTML|LIQUID)            Language to use for generating comments around TOC and anchors (default:
                                           HTML)
  --trim-toc / --no-trim-toc               Whether to indent TOC based on the registered headings, or based on the
                                           actual heading levels (default: true)
  --oneshot / --no-oneshot                 Whether to add comments so bitdowntoc can regenerate/update the toc and
                                           anchors (false) or not (true) (default: false)
  --max-level=<int>                        Maximum heading level to include to the toc (< 1 means no limit) (default:
                                           '-1')
  -p, --profile=(GENERIC|GITHUB|GITLAB|DEVTO|HASHNODE)
                                           Load default options for a specific site
  -i, --inplace                            Overwrite input file. This is incompatible with reading from stdin
  -o, --output-file=<path>                 Write the output to a file instead of stdout
  -h, --help                               Show this message and exit

Arguments:
  <path>  Markdown file, or '-' to read from stdin

Native executables are attached to each release.

Linux

On Linux, you may just have to run chmod +x before use.

Mac

On Mac, you need to run chmod +x and then execute the script once. It will be blocked, but you can allow it anyway by going to System Preferences > Security and pressing "Allow Anyway". Once done, re-execute BitDownToc and click "Open" on the popup. You are good to go.

Windows

On Windows, right-click on the executable and press Properties. In the general tab under Security at the bottom, tick "Unblock". You can now execute it in the CMD. Note that it may take a while to launch, but only the first time ;)

This tool supports some profiles out-of-the-box: GitLab, GitLab 17 (version 17.0 and above), GitHub, and dev.to. The Generic profile is perfect for platforms such as BitBucket Server which do not generate anchor links on their own. Simply choose your flavor using the profile option (-p/--profile).

It is however highly customizable, and the options can also fit many other platforms. Here is a breakdown of the options (that differ from the defaults) to use for each.

• Generic → generate anchors (e.g. BitBucket Server)
• GitLab → concat spaces, do not generate anchors
• GitLab 17 → do not concat spaces, do not generate anchors
• GitHub → do not concat spaces, do not generate anchors
• dev.to → concat spaces, do not generate anchors, comment style = liquid, anchors algorithm = DEVTO
• hashnode → concat spaces, anchors prefix = "heading-", anchors algorithm = HASHNODE

• BitBucket.org (supports the [TOC] directly) → anchors algorithm = DEVTO, anchors prefix = markdown-header- ❗ will break if you use code in your headings (backticks) - open an issue if you want support :)

If you have more ideas or platforms you want to use, let me know by opening an issue 😊.

If no combination of available options fits your Markdown processor, simply use the generate anchors (or use the BitBucket profile).

Since the anchors are manually added to the markdown, the TOC will work as long as <a> tags with a name parameter are supported. If you are working with a platform supporting liquid tags instead (e.g. forem), set the comment style option to LIQUID (or use the dev.to profile).

You can control where the table of content will be inserted by adding the marker (on its own line):

[TOC]

Any header above the marker will be ignored. The option "trim toc" (turned on by default) means that if you have e.g. only level-2 headers below the marker, the TOC will be indented as if those were level 1 headers.

I got the motivation from the lack of existing tools supporting BitBucket Server. As of version 6, the BitBucket processor doesn't insert any ID or name to the HTML headers generated from markdown, meaning there is no way of targeting a specific header without manually adding an anchor of the form:

<a name="some-heading"></a>

I found this blog mentioning a Vim plugin doing it for you, but this requires Vim (obviously) and the anchors support lives in a specific branch that is unlikely to be maintained.

I am quite fond of GitHub Wiki TOC generator (you should see the inspiration here), and wanted something similar but more flexible (not only targeting GitHub and supporting symbols and diacritics).

This project was also a great way to play with Kotlin MPP (Multi-Platform Projects).

The code is split between:

• a common module handling the TOC generation, and defining the default options;
• a JVM module with a Clikt CLI;
• a JS module that is imported into a static HTML page.

Tests are implemented in the common module, with one exception: some additional tests are located in the JVM module, because I wanted to load test files and reading files is not supported in common...

To build the project, use the custom target bitdowntoc, which will produce the JVM fat jar and copy the compiled js scripts into the directory html/scripts:

./gradlew bitdowntoc

The html folder can then be deployed as a static site.

To run tests, use check or allTests:

./gradlew allTests

If you find this tool helpful, please star the repo or add a comment somewhere, it will help me keep enough motivation to maintain it properly.

If you want to contribute, feel free open a PR anytime! Just keep in mind:

• code style → Kotlin Coding Conventions
• commit messages → conventional commits
• pull requests policy → rebase + squash (one commit per PR, rebased on the main branch)
• build and run → see sections above 😏

I chose the Common Clause for this project, just because I had a very bad experience once, where someone took one of my projects as is, added adverts and republished it under his own name.

I know most of the Open Source community isn't like that, but bitdowntoc is unlikely to be used in a commercial product anyway. Thus, the license is only here to ensure no one will suddenly make a non-free bitdowntoc clone.

If you have any problem with this, feel free to share your thoughts in an issue, I will be glad to discuss (and maybe revisit) it!

Until then, please to do whatever you want with bitdowntoc, as long as your heart is pure.