Tag fenced code blocks with the right language
Scan a Markdown document for unfenced or untagged code blocks and auto-detect the language so GitHub and other renderers can apply syntax highlighting.
# Snippets
```javascript
const x = 1;
function add(a, b) { return a + b; }
```
```python
def hello():
print("hi")
```
```sql
SELECT id FROM users WHERE active = 1;
```How to auto-tag code blocks
Walks every fenced block, leaves existing tags alone, and runs heuristic regex on untagged content to guess the language. Conservative — emits no tag if confidence is low.
- 01
Paste Markdown
Especially old READMEs with untagged fences.
Parsing runs through marked with GFM extensions enabled — tables, task lists, strikethrough, and fenced code blocks all match GitHub’s rendering.
inputGFMmarkedCommonMarkliveinput · markdownmd · GFM``` x=1 ```
loaded · GFMGFM · ready - 02
Detect language
Heuristics check keywords, sigils, and structure.
Soft-break behaviour is configurable: by default a single newline becomes a space (CommonMark), toggle on for chat-style
<br>insertion.detectsoft-breaksoptionsconfiglivescan · optionslang · livedetected: python
options applied · livelive - 03
Inject tags
Adds the language string to the opening fence.
The preview is scoped under a
.mdeclass so its CSS doesn’t bleed into the rest of the page. Output HTML is whitespace-controlled for clean diffs.tagpreviewscoped CSSrenderstableout · renderedmd · ready```python
rendered · liverendered - 04
Push to GitHub
Highlighted code in PR previews and docs sites.
Export covers both raw Markdown and rendered HTML; downloads stream as
text/markdownortext/htmlviaBlob+ object URL.exportclipboard.md.htmlblobOK · exportedgh · donehighlighted
shipped · ready to shipsuccess
Author Markdown that renders everywhere
GFM is the safe default
GitHub-Flavored Markdown is the de-facto baseline (tables, task lists, strikethrough). CommonMark is stricter but ubiquitous as a fallback.
Soft-break behaviour varies
A single newline is a space in CommonMark, a <br> in GFM. Toggle soft breaks when source matters.
Escape inside code fences
Backticks inside fenced blocks need a longer fence — three becomes four. Use ~~~ if your content has many backticks.
Anchors are slugified
GitHub lowercases, strips punctuation, and joins with hyphens. Duplicate headings get -1, -2 suffixes.
Tables need a header row
The dash row sets alignment (:---, :-:, ---:). Use Table Aligner for diff-friendly columns.
Front matter is YAML
Triple-dash blocks at the top of files are parsed by static-site generators. Use the Front-Matter Validator to catch syntax errors.
When to auto-tag
Legacy READMEs, doc sites, snippet libraries.
Legacy READMEs
Retro-tag untagged fences in old projects. Render path uses marked with GFM extensions enabled (tables, task lists, strikethrough, autolinks), so what you preview matches what GitHub publishes bit-for-bit. Soft-break behaviour is configurable for chat-style vs prose Markdown.
GFM-compliantDoc site upgrade
Prep content for a syntax-highlighting docs theme. Pairs cleanly with the Markdown Cheatsheet for syntax you can't quite remember — callout blocks, footnotes, definition lists. Output stays diff-friendly so style-only changes don't drown out real edits in PRs.
GitHub-perfectSnippet library
Normalize a personal snippet collection. Cross-platform safe: anchors, code fences, and tables behave identically on GitHub, GitLab, Bitbucket, and Gitea. Heading-anchor slugs follow GitHub's lowercase-and-hyphenate rules so deep links survive a docs migration.
diff-friendlyTutorial polish
Make a workshop guide read like a real docs page. No server roundtrip — perfect for proprietary content you can't paste into a public tool. The full marked + GFM bundle ships with the page, so it works offline once loaded.
render-stableMigration
Tag fences when moving wikis to a new renderer. Front matter (YAML / TOML / JSON) passes through unchanged so static-site pipelines (Jekyll, Hugo, Astro, Eleventy) read it correctly. Pair with the Front-Matter Validator to catch syntax errors before deploy.
cross-platformSearch indexing
Some indexers rank tagged code higher. Output is reproducible: identical input always produces identical Markdown, so doc-generation scripts can rely on it for snapshot tests and embedded into release workflows.
SEO-friendlyFrequently asked questions
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