Free Syntax Highlighting in Blogger for Code Snippets

You pasted a CSS snippet into a Blogger post and it came out as one grey wall of text, with quotes curled and indentation gone. Readers trying to copy it will get errors. Adding syntax highlighting in Blogger fixes the look, but many old tutorials point to abandoned scripts that slow your page or break on mobile templates.

I customize Blogger templates for a living and have added code highlighting to more of them than I can remember. Here is the free, safe way to do it in 2026, plus the mistakes that quietly hurt page speed.

What you need for syntax highlighting in Blogger

Highlighting needs three pieces working together:

• A highlighter script that reads your code and wraps keywords, strings and comments in coloured spans.
• A theme stylesheet that decides the colours.
• Correct markup in each post, so the script knows where the code starts and what language it is.

Two free, open source libraries cover almost every blogger's needs: Prism and highlight.js. Both are actively maintained, both are released under permissive licences (MIT for Prism, BSD 3-Clause for highlight.js), and both can be loaded from a free public CDN such as jsDelivr or cdnjs without hosting files yourself. That makes them proper free resources rather than freeware with strings attached.

Prism or highlight.js for a Blogger site

For a typical Blogger tutorial site that shares template tweaks, I recommend Prism with only the markup, CSS and JavaScript languages. The whole thing usually weighs less than a small image.

Adding Prism to your template step by step

Back up your theme first. In Blogger, go to Theme, open the menu beside Customize, and choose Backup. Download the XML file and keep it safe.

1. Open Theme, then the menu beside Customize, then Edit HTML.
2. Find the closing head tag. Just above it, add a link element pointing to a Prism theme stylesheet from your chosen CDN. Okaidia and Tomorrow Night are popular dark themes; the default theme is light.
3. Find the closing body tag. Just above it, add a script element loading the Prism core file, then one script element for each extra language you need. Add the defer attribute so the scripts do not block the page from rendering.
4. Save the theme and open any post on your live blog to confirm nothing has broken.

If editing the theme HTML feels risky, the colour adjustments at least can live in the Customize panel, as explained in our guide on adding custom CSS in Blogger without editing HTML. The scripts themselves still need the HTML editor.

Marking up code inside a post

Switch the post editor to HTML view. Wrap each snippet in a pre element containing a code element, and give the code element a class naming the language, such as language-css or language-markup. Any angle brackets inside the snippet must be escaped as HTML entities, or Blogger will treat them as real tags and strip them. A free online HTML escaper does this in one paste.

Never paste code in Compose view. The editor converts straight quotes into curly ones and collapses spaces, which is exactly the damage you are trying to avoid.

Why you might not need a highlighter at all

Most tutorials assume every blog with code needs a full highlighting library. I disagree for blogs that share a snippet once a month. A plain pre block styled with a monospace font, a light background, 14 or 15 pixel text, comfortable padding and horizontal scrolling is clear, accessible and costs zero extra requests.

Colour also has a readability downside. Many popular dark themes have comment colours with contrast ratios well below the 4.5 to 1 level recommended for body text, so readers on phones outdoors struggle to see them. If you do add a highlighter, check your theme's comment and string colours with a contrast tool and adjust them in your CSS.

My rule of thumb: if code appears in fewer than one post in five, use styled pre blocks. Past that, a highlighter earns its place. Either way, keep fonts light; our article on free fonts and icons that do not slow down your site covers monospace options that load fast.

Avoiding the old SyntaxHighlighter trap

Search results still recommend Alex Gorbatchev's SyntaxHighlighter, often loaded from files hosted on a stranger's server. That project has not had a meaningful update for Blogger users in years, it loads a large set of files, and if the hosting disappears your code blocks break across every post at once. Some older Blogger templates bundle it already. If yours does, remove those script and stylesheet lines before adding Prism, or you will load two highlighters on every page. When choosing templates in general, the checks in where to find free templates that are not actually malware apply to scripts too: prefer well-known open source projects served from reputable CDNs.

Quick fixes for common problems

• Code shows but has no colour: the class is missing or misspelled. It must start with language followed by a hyphen.
• Tags disappear from HTML snippets: the angle brackets were not escaped.
• Long lines push the layout sideways on mobile: add overflow-x set to auto on pre elements in your CSS.
• Highlighting flashes in late: normal with defer, and better than blocking the page. Keep it.

Frequently asked questions

Is Prism free to use on a Blogger blog?

Yes. Prism is open source under the MIT licence, which allows free use on personal and commercial blogs. Keeping the licence comment inside the script file is all it asks.

Why does Blogger remove my code when I publish?

Blogger reads unescaped angle brackets as real HTML and strips or renders them. Escape the snippet into HTML entities and paste it in HTML view, not Compose view.

Does syntax highlighting slow down a Blogger site?

A lightweight setup like Prism with three languages and deferred loading adds very little. Large bundles, old libraries and loading two highlighters at once are what cause noticeable slowdowns.