Reading Markdown with Crumbs

Crumbs formats eligible standalone Markdown documents and provides heading navigation in both views. Choose Rendered for the reading view or Raw for the original Markdown text.

Crumbs remembers Raw-view choices locally for up to 500 documents. Choosing Rendered removes that document’s exception. Document contents are never saved.

Supported syntax

Feature	Syntax or example	What Crumbs renders
Headings	# Title through ###### Heading	Headings that also appear in the outline.
Emphasis and inline code	*italic*, **bold**, ~~strike~~, and `code`	Styled text and inline code.
Lists and quotes	- Item, 1. Item, - [x] Done, and > Quote	Bulleted and numbered lists, task lists, and block quotes.
Links and images	[Label](url), , and plain web or email addresses	Links and images. Relative image paths resolve against the original document URL.
Tables	Pipe-delimited rows with a --- header separator	Tables that scroll horizontally when wider than the reading column.
Code blocks	Triple backticks with an optional language, such as js	Code with copy and wrap controls. Supported languages get syntax highlighting.
Footnotes and definitions	[^note] with [^note]: Text, or a term followed by : Definition on the next line	Linked footnotes and definition lists.
Alerts	> [!NOTE] followed by quoted text	GitHub-style Note, Tip, Important, Warning, and Caution callouts.
Emoji	:sparkles:	Emoji from supported shortcodes.
Mermaid	A fenced code block labeled mermaid	A diagram with pan, zoom, and source copy controls.
Math	$x^2$ inline, or $$ delimiters for display math	KaTeX-rendered math. \( ... \) and \[ ... \] delimiters also work.
YAML front matter	A YAML block at the start of the file between --- delimiter lines	A collapsible Metadata panel, separate from the heading outline.
Theme-aware pictures	<picture> with <source media="(prefers-color-scheme: dark)" srcset="dark.png"> and an <img> fallback	The appropriate image for the reader’s light or dark theme.
Supported HTML layouts	<details>, <summary>, <table>, and <img>	Expandable disclosures, tables, and images with supported layout attributes.

Code blocks show their declared language. Blocks without a declared language show plaintext; Crumbs does not guess the language.

Front matter stays in the original source when you switch to Raw or copy the full document. If YAML parsing fails, the Metadata panel shows the source and the article body still renders.

Supported README layouts can preserve image sizes, centered headings and paragraphs, table cell widths, and vertical alignment. Wide tables can also be scrolled with the keyboard.

Choose a reading theme

Markdown defaults to System, following your system’s light or dark appearance. Select Light, Dark, or System from the palette icon at the document’s top right, or under Readers → Reader appearance in the extension popup.

This preference saves locally and applies across open Markdown and JSON documents in both Rendered and Raw views. It is independent of the Glazed/Plain style and Plain theme used by the floating outline. Mermaid diagrams use a light canvas in either reading theme.

Copy Markdown, code, or diagram source

• Copy raw Markdown, at the document’s top right in either view, copies the entire original source, including formatting and front matter. It remains available when the floating outline is hidden.
• The copy button above a code block copies its text with indentation and line breaks, without Markdown fence markers.
• The copy button beside a Mermaid diagram’s zoom controls copies the original diagram source, rather than an image.

Copy controls show hints on hover or focus and a short confirmation after success. Crumbs writes to the clipboard only after you select a Copy control; it does not read the clipboard.

For Mermaid diagrams, drag to pan, use the zoom controls, or select the percentage to reset to fit.

Automatic rendering

Open Readers → Markdown reader in the popup. Enable the reader, then open More options → Render automatically. Under Websites, choose All detected Markdown or Only matching URLs.

For matching URLs, enter domains or wildcard patterns separated by commas. These use the same domain and pattern syntax as General’s Specific sites and Except these lists. For example, example.com/* matches one domain, *.example.com/* includes its subdomains, and localhost/* matches localhost on any port.

Use Add current site, remove entries individually, or open the list menu for Copy all and Clear all. Undo can restore a cleared list while its feedback is visible. Invalid batches are not partially added; duplicates are ignored.

Older saved Domain, URL contains, and URL wildcard rules retain their original labels and matching behavior until removed. New entries use the shared pattern syntax. In particular, older Domain rules may include subdomains, and older URL contains rules may match query strings; new rules ignore query strings and fragments.

These settings do not convert ordinary HTML pages, GitHub’s already-rendered file pages, code snippets inside web pages, or files delivered as downloads. Manual Rendered and Raw switching remains available for detected Markdown documents when automatic rendering is off. Rendering settings are separate from Show/Hide, which controls the floating outline.

Local Markdown files

Reload after changing reader settings; the shared reader theme updates immediately.

Local Markdown is off by default:

1. Open the Crumbs popup’s Readers tab.
2. Enable Local Markdown files.
3. Select Open extension settings if One more step required appears.
4. On Crumbs’ Chrome Details page, enable Allow access to file URLs.
5. Refresh the Markdown file.

Both settings are required. A green permission dot indicates that Chrome’s file access is granted. Local Markdown works independently of the Specific sites and Except these lists. Show/Hide does not remove the formatted document; you can still choose Rendered or Raw from the document control.

Crumbs does not edit files or watch the disk for changes, so refresh the page after editing a local file. Local images also need Chrome’s file-access permission.

HTML shown as source

Markdown can include HTML. Crumbs renders a supported subset, including tables and expandable disclosures. Unsupported or restricted HTML appears as its original markup with an information icon ⓘ. Hover over or focus the icon for details.

The icon does not necessarily mean the document is harmful. Scripts, embedded frames, and forms are restricted intentionally; other elements can be harmless but outside the supported formatting. Code examples inside backticks or fenced blocks stay ordinary code examples.

Unsafe attributes, event handlers, and links are removed. Arbitrary source CSS is not preserved. Original markup remains available in Raw view, and Crumbs does not change the source file.

Formatting limitations

Markdown dialects vary, so site-specific mentions, issue references, and custom syntax may remain plain text. Crumbs does not promise identical results for every GitHub page or Markdown extension.

Image dimensions are bounded. Theme-aware picture sources support light/dark color-scheme queries, rather than arbitrary media queries or CSS. Images may still depend on access to their original host.

Document-supplied Mermaid configuration and interactive callbacks are not enabled. If a diagram or formula cannot be rendered, Crumbs keeps its source readable. Code languages without highlighting support remain plain code.