Markdown Viewer / Browser Extension

Install: Chrome / Firefox / Edge / Opera / Brave / Chromium / Vivaldi

Features

• Secure by design
• Render local and remote file URLs
• Granular access to remote origins
• Multiple markdown parsers
• Full control over the compiler options (markdown-it, marked, remark)
• 30+ Themes (cleanrmd, GitHub)
• Custom theme support
• GitHub Flavored Markdown (GFM)
• Auto reload on file change
• Syntax highlighted code blocks (prism)
• Table of Contents (ToC)
• MathJax formulas (mathjax)
• Mermaid diagrams (mermaid)
• Convert emoji shortnames (icons provided free by EmojiOne)
• Remember scroll position
• Markdown Content-Type detection
• Configurable Markdown file path detection
• Settings synchronization
• Raw and rendered markdown views
• Free and Open Source

Table of Contents

• After Install
• Themes
• Compiler Options
• Content Options
• Manage Origins
• Syntax Examples

Additional documentation specific to Firefox

After Install

Local Files

1. Navigate to chrome://extensions
2. Locate the Markdown Viewer extension and click on the Details button

3. Make sure that the Allow access to file URLs switch is turned on

Remote Files

1. Click on the Markdown Viewer icon and select Advanced Options
2. Add the origins that you want enabled for the Markdown Viewer extension

---

Themes

All themes support the following width options:

• auto - automatically adjust the content width based on the screen size
• full - 100% screen width
• wide - fixed at 1400px
• large - fixed at 1200px
• medium - fixed at 992px
• small - fixed at 768px
• tiny - fixed at 576px

The auto option on the github and github-dark themes has a fixed width with a surrounding border identical to a rendered README.md file for a repository hosted on github.com

Custom Theme

1. Go to the Advanced Options and click on Settings
2. Select CUSTOM for Content Theme
3. Upload your Custom Theme below
4. Specify the Color Scheme of your theme

Your custom theme will be minified automatically on upload and it can be up to 8KB in size.

You can add <link rel="stylesheet" type="text/css" href="file:///home/me/custom-theme.css"> to your markdown document to speed up development while working on your theme. Custom theme example.

---

Compiler Options

Full CommonMark support including GFM tables and strikethrough +

Option	Default	Description
abbr	false	Abbreviation using *[word]: Text <abbr>
attr	false	Custom attributes using {} curly brackets
breaks	false	Convert new lines \n in paragraphs into line breaks <br>
cjk	false	Suppress linebreaks between east asian characters
deflist	false	Definition list <dl>
footnote	false	Footnotes [^1] [^1]: a
html	true	Enable HTML tags in source
ins	false	Inserted text ++a++ <ins>
linkify	true	Autoconvert URL-like text to links
mark	false	Marked text ==a== <mark>
sub	false	Subscript ~a~ <sub>
sup	false	Superscript ^a^ <sup>
tasklists	false	Task lists - [x]
typographer	false	Enable some language-neutral replacement + quotes beautification
xhtmlOut	false	Use / to close single tags (<br />)

---

Content Options

Option	Default	Description
autoreload	false	Auto reload on file change
emoji	false	Convert emoji :shortnames: into EmojiOne images
mathjax	false	Render MathJax formulas
mermaid	false	Render Mermaid diagrams
syntax	true	Syntax highlighted fenced code blocks
toc	false	Generate Table of Contents

Autoreload

When enabled the extension will make a GET request every second to markdown files hosted on:

• file:/// URLs
• any host that resolves to localhost IPv4 127.0.0.1 or IPv6 ::1

Emoji

Convert emoji :shortnames: into EmojiOne images:

• Emoji shortnames like :smile: will be converted to 😄 using EmojiOne images.
• Currently unicode symbols like 😄 and ASCII emoji like :D are not supported.

MathJax

The following MathJax delimiters are supported:

• inline math: \(math\) and $math$
• display math: \[math\] and $$math$$

The following rules apply to your markdown content when MathJax is enabled:

• Regular dollar sign $ in text that is not part of a math formula should be escaped: \$
• Regular markdown escaping for parentheses: \( and \), and brackets: \[ and \] is not supported. MathJax will convert anything between these delimiters to math formulas, unless they are wrapped in backticks: `\(` or fenced code blocks.

Mermaid

Render Mermaid diagrams wrapped in mmd or mermaid fenced code blocks:

```mmd
sequenceDiagram
```

Alternatively diagrams can be wrapped in HTML tags:

<pre><code class="mermaid">
  sequenceDiagram
</code></pre>

• resize the diagram container vertically by dragging the bottom right corner of the code block up or down
• zoom in and out by holding down the Shift key and then using your mouse wheel
• pan by holding down the left mouse button and drag in any direction

Syntax

Syntax highlighting for fenced code blocks:

```js
var hello = 'hi'
```

Alternatively code blocks can be wrapped in HTML tags:

<pre class="language-js"><code class="language-js">var hello = 'hi'</code></pre>

Full list of supported languages and their corresponding aliases to use.

ToC

Generates Table of Contents (ToC) based on the headers found in the markdown document.

---

Manage Origins

Click on the Markdown Viewer icon and select Advanced Options.

By default Markdown Viewer does not have access to any content:

Enable File Access

To enable access to file URLs follow these steps.

In case access to local files was not enabled, an additional Allow Access button will be present next to the File Access header:

Clicking on it will point you to the built-in management page for the extension where you can toggle the Allow access to file URLs switch to enable it.

Enable Site Access

Access to individual sites can be enabled by copy/pasting a URL address into the Site Access text box and then clicking on the Add button next to it:

Access to both http and https protocols can be enabled by using a wildcard *://raw.githubusercontent.com

Access to all subdomains for a given hostname can be enabled by using a wildcard https://*.githubusercontent.com

Access to all ports on localhost can be enabled by adding http://localhost. Access to a specific port can be enabled by adding http://localhost:3000

Allow on All Sites

Access to all sites can be enabled by clicking on the Allow All button next to the Site Access header:

This is identical to adding the *://* pattern into the text box.

Content Detection

Each enabled origin has an option for content type header detection and path matching regular expression:

Header Detection

When this option is enabled the extension will check if the content-type header with a value of text/markdown, text/x-markdown or text/plain is present.

Path Matching

When this option is enabled the extension will check if the page URL matches the Path Matching RegExp.

The default regular expression is: \.(?:markdown|mdown|mkdn|md|mkd|mdwn|mdtxt|mdtext|text)(?:#.*|\?.*)?$

It is a simple regular expression that matches URLs ending with:

• markdown file extension: \.(?:markdown|mdown|mkdn|md|mkd|mdwn|mdtxt|mdtext|text)
• and optionally a hash or a querystring after that: (?:#.*|\?.*)?

The ?: used in (?:match) stands for non-capturing group and it is there for performance reasons.

You can modify the path matching regular expression for each enabled origin. The settings are being updated as you type.

Path Matching Priority

The enabled origins are matched from most to least specific:

1. https://raw.githubusercontent.com
2. https://*.githubusercontent.com
3. *://raw.githubusercontent.com
4. *://*.githubusercontent.com
5. *://*

The matching origin with the highest priority will be picked and its header detection and path matching settings will be used to determine if the content should be rendered or not.

It is recommended to explicitly allow only the origins that you want the extension to have access to.

Remove Origin

Click on the Remove button for the origin that you want to remove. This removes the permission itself so that the extension can no longer access that origin.

Refresh Origin

The extension synchronizes your preferences across all of your devices if you have logged into your browser and enabled the sync feature. The list of your allowed origins is being synced too. However, the actual permissions that you grant using the consent popup cannot be synced.

In case you have enabled a new origin on some of your devices you will have to explicitly allow it on your other devices. In this case the origin will be highlighted and an additional Refresh button will be present:

Only origins that needs to be refreshed will be highlighted. The extension cannot access highlighted origins unless you click on the Refresh button.

In some cases access to previously allowed origins may get disabled. Make sure you check back the advanced options page or reload it and look for highlighted origins that needs to be refreshed.

---

Syntax Examples

Examples about the Markdown syntax and all features available in Markdown Viewer can be found on GitHub, GitLab and BitBucket:

• elements.md - quick overview of the Markdown syntax and a summary of the Markdown Viewer features
• syntax.md - extensive list of Markdown syntax examples with different combinations and edge cases
• prism.md - syntax highlighting examples
• mermaid.md - different types of Mermaid diagrams
• mathjax.md - MathJax examples and support documentation

Allow the appropriate remote origin or pull any of the above repositories and access it on the file:/// origin locally.

---

Manual Install

The following instructions applies for: Chrome, Edge, Opera, Brave, Chromium and Vivaldi.

Note that in any of the following cases you won't receive any future updates automatically!

Load packed .crx

1. Go to releases and pick a release that you want to install
2. Download the markdown-viewer.crx file
3. Navigate to chrome://extensions
4. Drag and drop the markdown-viewer.crx file into the chrome://extensions page

Load unpacked .zip

1. Go to releases and pick a release that you want to install
2. Download the markdown-viewer.zip file and extract it
3. Navigate to chrome://extensions
4. Make sure that the Developer mode switch is enabled
5. Click on the Load unpacked button and select the extracted directory

Build

1. Clone this repository
2. Execute sh build/package.sh chrome (or firefox to build for Firefox)
3. Navigate to chrome://extensions
4. Make sure that the Developer mode switch is enabled
5. Click on the Load unpacked button and select the cloned directory

Manifest v2

1. Clone the mv2 or compilers-mv2 branch (Markdown Viewer v4.0)
2. Navigate to chrome://extensions
3. Make sure that the Developer mode switch is enabled
4. Click on the Load unpacked button and select the cloned directory

---

License

The MIT License (MIT)

Copyright (c) 2013-present, Simeon Velichkov simeonvelichkov@gmail.com (https://github.com/simov/markdown-viewer)

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.