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PyMarkdown is primarily a Markdown Linter. To ensure that the Markdown linting is accomplished successfully, the rules engine that powers the linter uses a Markdown parser that is both GitHub Flavored Markdown compliant and CommonMark compliant. The rules provided in the base application can be easily extended by writing new plugins and importing them into the rules engine through simple configuration options.
The PyMarkdown project has the following advantages:
- This project can examine multiple files and directories with one invocation, ensuring that all detected Markdown files adhere to the same guidelines.
- The linter runs on any system running Python 3.8 or later, with no modifications.
- The parser that powers the linter is GitHub Flavored Markdown (GFM) compliant. Due to that foundation, the parser does not guess how some parsers may handle a given situation, as it has a clear set of rules to follow.
- The parser passes all GFM conformance tests and CommonMark conformance tests. In test scenarios that were not present in either set of tests, the CommonMark 0.29.2 release was used to determine the correct parsing.
- Each Markdown document is parsed into an internal token format. Most of the rules and made more efficient by leveraging this token format. Where that is not possible, simple regular expressions and simple algorithms are used on a line-by-line basis.
- Thoroughly tested
- The project currently has over 4100 scenario tests and a coverage percentage of 100%.
- The parser for the project adheres to the GFM specification and most of the rules for the parser leverage the tokens produced by that parser. The rules themselves are plugins, so they are extensible by default. The parser itself will be extended as needed to provide for other Markdown extensions as needed.
- The PyMarkdown linter can be executed from a script on the command line, from within another Python program, or using the popular Git Pre-Commit hooks.
This project is currently in beta, and some of these documented things may not work 100% as advertised until after the final release. However, everything should be close enough to done that if you find something missing, please let us know.
GitHub Pre Commit Hooks
If you intend to use the PyMarkdown project as a linter for your GitHub Pre-Commit hooks, then refer to this document on how to set that up. Once setup, you can continue reading at the How To Use section for more information on the options available for use in your Pre-Commit Hooks.
This project required Python 3.8 or later to function.
pip install pymarkdownlnt
How To Use
If You Get Stuck
Full help support is available by entering
on the command line and pressing enter. For an individual command,
help is available by following the command or commands with
pymarkdown scan --help
Various sections of this document benefit from having concrete examples
to illustrate how things work. For the following sections,
this documentation will assume that there is a file called
in a directory called
examples that has the following content:
## This is an example Just an example.
and a file called
example-2.md in that same directory that has the
# This is an example Just an example.
If you prefer concrete files, these files are checked into the examples directory of the GitHub project.
The PyMarkdown linter is executed by calling the project from the
command line and
specifying one or more files and directories to scan for Markdown
files. The set of files and/or directories must be prefaced with the
scan keyword to denote that scanning is required. For the examples
directory, both this form:
pymarkdown scan examples
and this form:
pymarkdown scan examples/example-1.md examples/example-2.md
can be used to scan both files in the directory. The only difference
between the two invocations is that the first example will scan every
.md file in the
examples directory, while the second
invocation will only scan the two specified files. For clarity purposes,
if the command line specifies the same file multiple times, that file
name will only be added to the list of files to scan once.
If everything is working properly, both of the above scans will produce the following output:
examples/example-1.md:3:16: MD047: Each file should end with a single newline character. (single-trailing-newline)
The PyMarkdown project includes 13 out-of-the-box rules, with another 29 rules to be added before the 1.0.0 release. These rules are implemented using a simple plugin system that is documented in the developer documentation. It is these rules that allow the PyMarkdown project to scan the various Markdown files, looking for bad patterns over that set of Markdown documents.
Because of the way that the rules are provided, sometimes we
refer to the rules as
rules and sometimes as
rule plugins. A
is a specific set of conditions that trigger the reporting of a violation
when those conditions occur. A
rule plugin is the Python class
and Python file in which the
rule is supplied to the PyMarkdown application.
Our goal is to try to not use these phrases interchangeably, but we are only
human. If we do mess up and use the wrong phase, we do apologize.
Note that the initial set of rules are modelled after the 42 rules provided by David Anson's Markdown Lint project. This decision was made to give Markdown authors that use his project in their IDEs (such as the MarkdownLint plugin for VSCode that I use), a good grounding in what they can consistently check for.
Rule Violation Format
Executing either of the above example command lines will produce the following output:
/examples/example-1.md:3:16: MD047: Each file should end with a single newline character. (single-trailing-newline)
The format of the output for any rules that are triggered is as follows:
file-name:line:column: rule-id: description (aliases)
file-name- Path to the file that triggered the rule.
column- Position in the file where the rule was triggered.
rule-id- Unique identifier assigned to the rule.
description- Human readable description of the rule.
aliases- One or more aliases used to reference the rule.
For the rule violation that was reported at the start of this section,
the first step in diagnosing
that violation is to look at the file
/examples/example-1.md at the end of
line 3, which is column 16. Rule md047 specifies
that every file should end with a single newline character, which is
what is reported in the violation's description. Additionally, it reports that this
rule can also be identified by the more human readable alias of
The most frequently used part of the configuration system is the part that enables and disables specific rules while scanning the Markdown files. For example, if you do not like rule md047 which states that each file must end with a single newline, you can disable that rule by specifying:
pymarkdown -d md047 scan /examples
pymarkdown --disable-rules md047 scan /examples
The effect of disabling the rule should be evidenced by
the scan no longer reporting any violations of rule md047
against the Markdown file
Alternatively, rules can also be enabled. As the modelled base rules for this project are based off those rules for David Anson's project, rule md002 is disable by default in both projects. Specifically, rule md002 is disabled by default as rule md041 provides a better implementation of that rule that takes front-matter into account. Until that rule is implemented, you can enable rule md002 by specifying either:
pymarkdown -e md002 scan /examples
pymarkdown --enable-rules md002 scan /examples
The effect of enabling the rule is evidenced by
the scan reporting a violation of Rule md002 against
examples/example-1.md:1:1: MD002: First heading of the document should be a top level heading. [Expected: h1; Actual: h2] (first-heading-h1, first-header-h1) examples/example-1.md:3:16: MD047: Each file should end with a single newline character. (single-trailing-newline)
Extensions are any features that are implemented in addition to the base GitHub Flavored Markdown specification. These extensions are documented in the extensions document, including information about how they perform, details on the extension, and configuration information.
For more advanced scanning options, please consult the document on Advanced Scanning.
For more advanced configuration options, please consult the document on Advanced Configuration. This document includes information on:
Advanced Rule Plugins
For more information of how to query information on the rule plugins that are currently loaded, please consult the document on Advanced Rule Plugins.
Open Issues and Future Plans
During the development phase of this project, it was more useful to have an actual list of issues to track and prioritize, rather than relying on GitHub to do all the work. This is the location of the prioritized Issues List.
If you find any issues, please report them using the standard GitHub issues process. When our team looks at your issue and triages it, it will be added to our Issues List with the triaged priority. For us, this provides transparency as to what we are currently working on, what is up next, and what our plans are for further development.
When Did Things Change?
The changelog for this project is maintained at this location.
Still Have Questions?
If you still have questions, please consult our Frequently Asked Questions document.
If you would like to report an issue with the linter, a rule, or the documentation, please file an issue using GitHub.
If you would like to us to implement a feature that you believe is important, please file an issue using GitHub that includes what you want to add, why you want to add it, and why it is important. Please note that the issue will usually be the start of a conversation, and be ready for more questions.
If you would like to contribute to the project in a more
substantial manner, please contact me at
Instructions For Contributing
Developer notes on various topics are kept in the the Developer Notes document.
If you attempting to contribute something to this project, please follow the steps outlined in the CONTRIBUTING.md file.
Currently, as a team of one, there are only two big groups of people to acknowledge.
The first, and foremost group, is my immediate family. They have endured me coming out of my office with my head still in the clouds, explaining things to them so that I can think more clearly. While they still do not understand what I am talking about with respect to this project, I am so grateful to them for allowing me to work "my process" to figure things out.
The second group is the contributors to the CommonMark discussion forum. While I have raised some issues that were cut and dry, a lot of them involved significant amount of discussion to figure out what the right approach is. Through all those discussions, I rarely, if ever, felt like they treated me as less than equal, no matter how stupid my questions were. For their patience and their professionalism, thank you.