Verify File Association Settings
The most common cause for missing syntax highlighting is an incorrect file association. If Codium does not recognize .md files as Markdown, it will treat them as plain text. First, open any Markdown file in the editor. Look at the bottom right corner of the status bar where the language mode is displayed. If it says "Plain Text" or "Unknown," you need to change it.
Click on the language indicator in the status bar and select "Markdown" from the dropdown list. This action changes the view for the current file only. To make this change permanent for all future Markdown files, you must update your user settings. Open the Command Palette by pressing Ctrl+Shift+P (or Cmd+Shift+P on macOS) and type "Configure File Association for '.md'". Select this option and ensure that markdown is the primary language associated with the .md extension. This step ensures that every time you open a new document, Codium applies the correct syntax rules immediately.
Install Essential Extensions
Codium, being a free and open-source fork of Visual Studio Code, does not include all proprietary Microsoft extensions by default. While basic text editing works out of the box, advanced features like syntax highlighting often rely on specific community or Microsoft-hosted extensions. Navigate to the Extensions view by clicking the square icon on the left activity bar or pressing Ctrl+Shift+X.
Search for "Markdown" in the search bar. You will likely see two prominent options: "Markdown Language Features" and "Markdown All in One." The "Markdown Language Features" extension provides core syntax highlighting, preview capabilities, and link checking. Install this extension if it is not already present. If you find that the highlighting still appears broken or minimal, consider installing "Markdown All in One" as well, which adds additional formatting shortcuts and enhanced visual cues. Restart Codium after installation to ensure the extension hooks into the editor's grammar system correctly.
Check Theme Conflicts
Sometimes the issue is not with the Markdown parser itself, but with the color theme applied to the editor. A poorly configured theme may lack definitions for Markdown-specific scopes, causing headings, links, and code blocks to appear in the same color as regular text. Go to File > Preferences > Color Theme and cycle through different installed themes. Try switching to a standard theme like "Dark+" or "Light+" to see if the highlighting returns.
If a custom theme breaks Markdown syntax, you have two choices. First, you can switch back to a known-good theme while you investigate the custom one. Second, you can edit the theme's JSON file to add missing scope mappings. For most users, simply switching to a default theme resolves the visibility issue. Ensure that your theme is compatible with the version of Codium you are running, as older themes may not support newer grammar updates.
Validate Grammar Files
In rare cases, the underlying TextMate grammar file used by Codium to parse Markdown may be corrupted or missing. This usually happens after a failed update or manual modification of the extension folders. To diagnose this, open the Developer Tools by pressing Ctrl+Shift+I (or Cmd+Option+I on macOS). In the console tab, look for any errors related to "grammar" or "syntax." If you see errors indicating that a grammar file could not be loaded, it suggests a deeper installation problem.
To fix this, you may need to reinstall the Markdown extension. Uninstall the current Markdown extension from the Extensions view, then reinstall it. This forces Codium to re-download and register the grammar files. Additionally, check if you have any local overrides in your workspace settings that might be disabling syntax highlighting. Open your workspace settings JSON file and look for keys like editor.tokenColorCustomizations or files Associations that might be interfering. Remove any suspicious entries and reload the window.
Alternative Configuration Methods
If the graphical interface methods do not resolve the issue, you can manually configure file associations via the settings JSON file. Open the Command Palette and select "Preferences: Open Settings (JSON)." Add the following entry to the files.associations object:
"*.md": "markdown"This explicit declaration overrides any default behavior and forces Codium to treat all files ending in .md as Markdown documents. Save the file and reopen your Markdown documents. This method is particularly useful if you are working in a multi-root workspace where folder-specific settings might be overriding user preferences. It provides a robust fallback when UI-based configuration fails.
For more information on managing code analysis and syntax rules in other languages, you might find How to Change VSCode Code Analysis Mode for C helpful, as the principles of extension management and grammar configuration are similar across different programming languages. Additionally, understanding how to manage file states is crucial when debugging syntax issues, so reading Open file from previous commits without overwriting working copy can help you recover previous configurations if a recent change broke your setup.
Frequently Asked Questions
Why does my Markdown preview show raw HTML?
This happens when the Markdown extension is not active or the file is not recognized as Markdown. Ensure the language mode in the status bar is set to "Markdown." If it is, try restarting the editor to refresh the preview engine. The preview relies on the same grammar as the syntax highlighting, so fixing one usually fixes the other.
Can I use custom CSS to fix missing highlights?
No, syntax highlighting is determined by TextMate grammars, not CSS. CSS controls the visual styling of the editor, such as font size and background colors, but it cannot define which tokens are colored red or blue. You must rely on the extension's grammar file to assign semantic scopes to your text.
Does Codium support GFM (GitHub Flavored Markdown)?
Yes, the standard Markdown extensions in Codium support GitHub Flavored Markdown, including tables, strikethroughs, and task lists. If these features are not highlighted, ensure you have the latest version of the "Markdown Language Features" extension installed. Older versions may have limited GFM support.
What should I do if the extension marketplace is inaccessible?
If you cannot access the internet within Codium, you can download the extension .vsix file from the official GitHub releases page on another computer. Transfer the file to your machine and install it using the "Install from VSIX" option in the Extensions view. This allows you to manually patch the editor without network connectivity.
Are there risks in manually editing grammar files?
Editing grammar files directly carries a risk of breaking syntax highlighting entirely if the Regular Expressions are malformed. It is generally safer to disable extensions or switch themes rather than modifying internal grammar JSON files. Only attempt manual edits if you have a backup of the original files and understand the structure of TextMate grammars.