I noticed that sometimes my code gets highlighted in different colors when rendered.
Syntax highlighting allows code in posts to be highlighted based on the language it's written in, to make it easier to read.
When creating or editing posts, syntax highlighting is assigned to the preview based on question's tags as soon as you stop typing for 5 seconds.
Stack Exchange does not have its own syntax highlighting engine. It uses highlight.js, and may not necessarily be using the latest release of that library. Therefore, any bugs and feature requests regarding syntax highlighting cannot be handled by Stack Exchange.
The full list is available on Meta. If syntax highlighting is not enabled on a site, follow the instructions at the bottom of the answer there.
In case of a tag name, make sure to also specify it in lower case. See How do I use syntax highlighting? section below for more info.
Not all languages supported by highlight.js are supported on Stack Exchange. See Language codes currently available on Stack Exchange below for the list of supported languages. If your language is not on the list, whether or not it is otherwise supported by highlight.js, follow the instructions in How do I report a bug or request a new language? section below.
Each tag may have a highlighting language specified in its properties. Visit the tag's wiki page to see it: click on the tag you've found at step 2 (such as javascript), then click "Learn more...". The language code that is currently being used for the tag (if any) will be displayed at the very bottom, below the wiki buttons:
If the tag doesn't have a highlighting language specified when it should, create a feature-request on your site's per-site meta to request it. (Only moderators can change the highlighting language for a tag.)
By default, Stack Exchange uses the tags on a question to determine the language you are using. If there's more than one tag that has a highlighting language specified, it lets highlight.js infer what's the best language to use. If none of the tags have one, no syntax highlighting will be performed. The question's tags are also used to determine the default syntax highlighting language for its answers.
Go to the list of existing issues in highlight.js GitHub repository and check to see if your request is already filed there, and if not, post it there.
If your bug fix or feature request has already been fixed or implemented by highlight.js but isn't working here, please wait, as new versions of highlight.js are deployed on the sites on a scheduled basis, and the latest version hasn't been deployed yet. (If it hasn't been deployed after a long time, you can post a feature request here on Meta asking that Stack Exchange update to the latest version.)
Keep in mind that Stack Exchange does not maintain this syntax highlighter (aside from installing newer versions of it), and posting bug reports or feature requests concerning it here on Meta will not get them fixed or implemented.
Before you do anything, make sure that you've got the correct highlighting turned on.
If a language is already on the list of languages supported by highlight.js, but is not supported on Stack Exchange (see Language codes currently available on Stack Exchange below), you can raise a feature request here on Meta to ask for it to be deployed on the network.
However, do note that requests for supporting more languages are extremely likely to be considered low-priority and as such deferred. The current response for such feature requests is that the team finds that the added trade-offs from supporting more languages outweigh their potential benefit, though they're looking for future ways to lighten it.
Follow the instructions in Reporting a bug or requesting a feature for a language supported on Stack Exchange above to request that highlight.js support your new language. Once the language is supported by highlight.js, follow Requesting that Stack Exchange support a new language which is already supported by highlight.js to make it available here on Stack Exchange.
As long as all the conditions in the Why isn't my code being highlighted correctly? section above are satisfied, highlighting of code blocks will kick in automatically based on the question's tags. (See 3. Check that the tags on a question have an associated language codes section above for how this works.) Inline code is not highlighted.
It is possible to explicitly override the default highlighting language in use on the post with your language of choice for a specific code block, by specifying a language hint above the code block. Note that this is only supported when using the code fence (```) method of code formatting; since the implementation of CommonMark, doing so on code blocks using the four-space indent method is no longer supported*:
```lang-or-tag-here
code goes here
```
You may use either a language code or a tag name in a language hint to activate syntax highlighting. See below for the complete list of language codes supported on Stack Exchange.
For example:
Here is a code block with language code (having the "lang-" prefix) as a hint:
```lang-js
function greet(person) {
return "Hello " + person;
}
var user = "Jon Skeet";
alert(greet(user));
```
Renders as:
function greet(person) {
return "Hello " + person;
}
var user = "Jon Skeet";
alert(greet(user));
Here is a code block with tag name (without "lang-" prefix) as a hint:
```typescript
var arr = [0, 1, 2]; // will highlight if [typescript] tag exists
```
Here on Meta Stack Exchange, this renders as:
var arr = [0, 1, 2]; // will highlight if [typescript] tag exists
If you don't want to have any syntax highlighting, you can use the lang-none language code:
```lang-none
[code here]
```
Renders as:
[code here]
You can also apply a language hint to all code blocks in your post, so you don't have to add a hint before each one, by adding an HTML comment at the top of your post. The hint will then be applied to all code blocks within your post, including those which use four-space indent or HTML <pre><code>:
<!-- language-all: lang-or-tag-here -->
Note that when used on a question, it does not override the highlighting language on its answers; those will still be highlighted by default as per the question's tags.
This is a complete list of every identifier that you can use in a language hint for syntax highlighting. All the language identifiers in each group point to the same highlighter. Other language aliases set by highlight.js (in parentheses) should work, but only identifiers before them are officially supported by Stack Exchange.
Note that, as mentioned before, this is a subset of all languages supported by highlight.js.
Format: Language name: lang-code, custom Stack Exchange aliases, (other Highlight.js aliases)
lang-plaintext, lang-none, (lang-text, lang-txt)lang-bash, lang-bsh, lang-csh, lang-shlang-c, lang-cyc, lang-m, lang-c-like, (lang-h)lang-clojure, lang-clj, (lang-edn)lang-coffeescript, lang-coffee, (lang-cson, lang-iced)lang-cpp, lang-cc, lang-cxx, (lang-c++, lang-h++, lang-hpp, lang-hh, lang-hxx)lang-csharp, lang-cs, (lang-c#)lang-csslang-dartlang-delphi, (lang-dpr, lang-dfm, lang-pas, lang-pascal)lang-erlang, lang-erllang-go, (lang-golang)lang-haskell, lang-hslang-http, (lang-https)lang-ini, (lang-toml)lang-java, (lang-jsp)lang-javascript, lang-js, (lang-jsx, lang-mjs, lang-cjs)lang-jsonlang-julialang-kotlin, (lang-kt, lang-kts)lang-latex, lang-texlang-lesslang-lisp, lang-cl, lang-el, lang-lsplang-lualang-makefile, (lang-mk, lang-mak, lang-make)lang-markdown, (lang-md, lang-mkdown, lang-mkd)lang-mathematica, lang-mma, (lang-wl)lang-matlablang-objectivec, (lang-mm, lang-objc, lang-obj-c, lang-obj-c++, lang-objective-c++)lang-ocaml, lang-fs, lang-mllang-perl, lang-pl, (lang-pm)lang-phplang-php-templatelang-protobuf, (lang-proto)lang-python, lang-py, lang-cv, (lang-gyp, lang-ipython)lang-r, lang-slang-ruby, lang-rb, (lang-gemspec, lang-podspec, lang-thor, lang-irb)lang-rust, lang-rc, lang-rslang-scalalang-scheme, lang-scm, lang-ss, lang-rktlang-scsslang-shell, (lang-console, lang-shellsession)lang-sqllang-swiftlang-typescript, (lang-ts, lang-tsx, lang-mts, lang-cts)lang-vbnet, lang-vb, lang-vbslang-vhdl, lang-vhdlang-xml, lang-html, lang-xsl, (lang-xhtml, lang-rss, lang-atom, lang-xjb, lang-xsd, lang-plist, lang-wsf, lang-svg)lang-yaml, (lang-yml)Any language identifiers used in a post that go unrecognized, are for languages that are not deployed on Stack Exchange, or are for tags that do not have a language hint specified in their data will be ignored and the code block will not be highlighted. Prior to October 2024, such identifiers would trigger an automatic language detection; however, at that time, this was changed so it no longer highlights on new and edited posts (older unedited posts weren't changed). Note that the editor preview still continues to use automatic language detection in this case; the above fix was only for submitted posts.
You can specify any tag that exists on the site, and Stack Exchange will use whatever language hint is currently associated with that tag to highlight the code block (which can be either null (no hint, no syntax highlighting), default (automatic language detection), or a specific language code). Keep in mind that by default all tags start off with null as their language hint.
You can also use the plain none keyword to manually specify no syntax highlighting, similar to using the lang-none code above.
* The former method of specifying a highlighting language can still be used for HTML code blocks: place an HTML comment <!-- language: lang-or-tag-here --> before the <pre><code> tags and it will work. This:
<!-- language: c -->
<pre><code>#include <stdio.h>
int main() {
printf("Hello World");
}
</code></pre>
will render as
#include <stdio.h>
int main() {
printf("Hello World");
}
Also, this former method hasn't been completely removed for four-space indented code blocks, but merely deprecated. While it will still work for the time being on four-space indented code blocks, it may/will be removed in the future.
Note to editors:
Please do not edit the above list manually.
Just because you type something in and it looks like it's highlighted correctly does not mean the identifier actually exists in the system. Keep in mind that invalid identifiers trigger an automatic language detection in the editor preview (they will result in no highlighting in the submitted post).
Not all the languages supported by highlight.js are available everywhere. The set of languages available depends on how the library is built or included. This means that several languages that are indicated as supported in the above linked list are not supported by Stack Exchange's version of highlight.js, as they are in separate modules which have not been deployed on Stack Exchange.
Because of these points, to update the list please use the script it was generated with and link to this script (or another Meta post which confirms an identifier's existence) in your edit summary.
Note to commenters:
The comments on this FAQ are for requesting clarification of something you might not understand in the FAQ so that it can be fixed. Please DO NOT ask if certain languages will be supported in the future. Follow the instructions in How do I report a bug or request a new language? section to request language support.
lang- prefix isn't redundant. As mentioned in the post above, ```lang-javascript tells the highlighter to use the JS highlighter directly, while ```javascript alone tells it to look at the highlighter set for the tag [javascript]. They aren't always the same (maybe most notably with [typescript] on Stack Overflow).
lang-default is used, I'd like to know which language highlight.js ultimately settled on based on the auto-recognition (since if I find one I like, I can manually specify it in future, as lang-default gives different results question to question even if I use the same language).
lang- specifier) is covered a few times; first under the "How do I use syntax highlighting?" heading, and then again under "Hinting: Tags".
https://github.com/highlightjs/project or SE Sites use own sets of colors ? Could we change color and tone of colors ?Language Categories=AllandThemes=Stackoverflow Lightare this theme exactly the same used on SE Sites ? Which language is used forlang-default?hljs.versionStringin your browser's console (F12) or use this script to check the version of Highlight.js; 2. SE uses its own colors; 3. According to sources, it may be a bit outdated (Updated: 2021-05-15), but generally it should be the same theme;lang-defaultis a mistake. By default Highlight.js errors out, but SE made it to use an automatic language detection instead.