# CSS Diagnostics

> Highlight potentially invalid or erroneous HTML markup

Canonical page: [https://chrome-stats.com/d/css-diagnostics](https://chrome-stats.com/d/css-diagnostics)

## Overview

- **ID:** `css-diagnostics`
- **Platform:** Firefox
- **Type:** Firefox add-on
- **Status:** Available
- **Publisher:** Atanas Atanasov
- **Category:** web-development
- **Version:** 1.0
- **Last updated:** 2019-04-21
- **First published:** 2019-04-21
- **Size:** 54 KB
- **Data as of:** 2026-09-06
- **Store listing:** [Firefox Add-ons Store](https://addons.mozilla.org/firefox/addon/css-diagnostics/)
- **Website:** [https://atanas.info](https://atanas.info/)

## Description

CSS Diagnostics is a Firefox add-on that highlights potential errors in your HTML markup. It outlines erroneous elements in yellow or red rectangles, indicating warnings or errors in your code. You can choose to fix these issues as per your requirement.

## Rankings

- #147,371 — Overall

## Permissions and access

### Permissions

- `activeTab`
- `storage`
- `contextMenus`

### Content script matches

- `<all_urls>`

## Safety

- **Risk impact:** Moderate risk impact
- **Risk likelihood:** Moderate risk likelihood

### Analysis details

- Allows access to all websites, posing a significant security risk as it can monitor and modify data from any visited site.
- This extension has low user count. Unpopular extensions may not be stable or safe.

> Some risk analysis details are omitted from this free response. [Upgrade to view the full analysis](https://chrome-stats.com/pricing).

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Source: [Chrome-Stats](https://chrome-stats.com/d/css-diagnostics)