comparison · LoupeKit vs Web Developer
LoupeKit vs Web Developer: which one should you install?
Web Developer is the toolbar this whole category descends from, free and open source, and the Developer tab in LoupeKit is modelled on its menu on purpose. Disable styles, outline headings and tables, show alt text, populate forms, view response headers, validate - over a hundred commands in one menu, on Chrome, Edge, Firefox and Opera, with around a million users on Chrome alone. If what you want is those switches and nothing else, it is the right tool and it costs nothing.
Disabling JavaScript, clearing the cache and resizing the window, for nothing: Web Developer. The same toggles plus detection, diagnostics and audits of the whole page: LoupeKit.
Web Developer
Free · 1,000,000 users · Chromium and Firefox
A toolbar button opening a menu grouped into Disable, Cookies, CSS, Forms, Images, Information, Miscellaneous, Outline, Resize and Tools. Its own help page says the Firefox build lost the Disable group when Firefox removed the APIs behind it, and that the extension needs access to every site for all of its features to work.
LoupeKit
24-hour trial · ten surfaces · Chromium and Firefox
The same switches on one tab - styles off, outlines on, forms filled, images revealed, headers read, every one reversible - and nine more tabs beside it: the stack with the evidence for each match, ranked diagnostics, an SEO reader, an accessibility surface and an audit of how much of the markup reads as generated.
Feature by feature
Where LoupeKit stops, and why
- Disable JavaScript
- It needs the contentSettings permission, which grants control over every site’s scripts, cookies and images rather than the tab LoupeKit was opened on. The Developer tab lists the row with that reason instead of leaving it out.
- Clear cache and history
- It needs the browsingData permission, which can erase history, cookies, passwords and downloads across the whole profile. Four permissions and no host access is the line this extension holds.
- Open source
- The source is not published. What can be checked without it is stated instead: four permissions, no host permissions, and every request the extension makes named on the privacy page.
The same jobs, side by side
Turn off JavaScript to see what the page does without it
WEB DEVELOPER One click on Chrome. This is the product, and it is the right tool for it.
LOUPEKIT Refused, with the reason on the row: it needs the contentSettings permission, which covers every site.
Turn the stylesheets off
WEB DEVELOPER All, linked, embedded or inline, from the CSS group.
LOUPEKIT The same four, plus print styles, border-box and browser defaults - and Reset puts all of it back.
Fill a long form with test data
WEB DEVELOPER Populate form fields, from the Forms group.
LOUPEKIT Fill with mock data, and Form stress to push each field past what it expects.
See the page at a phone’s width
WEB DEVELOPER Resize the window to a preset, or open responsive layouts.
LOUPEKIT Side-by-side frames at genuine device widths, without touching the window.
Find out what the page is built with
WEB DEVELOPER Not what it is for.
LOUPEKIT 2614 technologies, each row showing the marker, URL or header that matched.
Find what is overflowing the viewport
WEB DEVELOPER Outline positioned and floated elements and look.
LOUPEKIT A ranked list with the cause named per row.
Pick Web Developer if
If you need to switch JavaScript off, clear the cache or set the window to an exact size, which it does and this extension will not ask the permissions to do. Or if a free, open-source menu of switches you have known for years is the whole job - nothing here is worth paying for to replace that.
Pick LoupeKit if
If the switches are where the question starts rather than where it ends: what the page runs, what it ships, what overflows, what fails accessibility, and how much of it reads as generated, from a panel that holds no host permissions.
Run both
Reasonable. Keep Web Developer for the browser-level switches and reach for this when the question is about the page itself.
On permissions
The rows this page concedes are the permission story told the other way round. Web Developer’s Firefox listing asks for every site, browsing data, cookies and history, and its Chrome manifest adds content settings - which is what lets it disable scripts and clear the cache, and its help page says as much. LoupeKit requests four permissions and no host permissions, and lists the toggles that would need more as refusals with the permission named.
CHECKED 22 OCTOBER 2026
Every figure about Web Developer on this page was checked on that day against its Chrome Web Store and Firefox add-on listings, chrispederick.com, and the manifest in its public repository, and nothing here is quoted from a review. Where a fact is not published anywhere we can point at, the table says so rather than estimating it. Products change; if something above is out of date, write to info@apptiary.com and it will be corrected.
Web Developer and every other product name on this site are the trademarks of their own owners. LoupeKit is not affiliated with, endorsed by or sponsored by any of them.