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Browser Extensions · head to head

Greasemonkey vs JSON Viewer

Greasemonkey logo

Greasemonkey

Browser Extensions

The original userscript manager, for Firefox

From
Free
Rated
-
Full reviewWebsite
JSON Viewer logo

JSON Viewer

Browser Extensions

View JSON documents in the browser

From
Free
Rated
-
Full reviewWebsite

The short version

  • Each has a real cost: Greasemonkey firefox only. There is no Chrome, Edge or Safari build and there never has been.; JSON Viewer the project is MIT licensed open source code hosted on GitHub with no vendor and no paid tier
  • They diverge on capability: Greasemonkey covers Userscript execution, JSON Viewer covers JSON formatting.
  • Prices and features above were last checked on 15 September 2026.

Where they differ

Only the attributes on which Greasemonkey and JSON Viewer actually diverge.

Attributes where Greasemonkey and JSON Viewer differ
AttributeGreasemonkeyJSON Viewer
Pricing modelopen-sourcefree
PlatformsFirefoxChrome, Firefox, Edge
FoundedUnknown2015

Identical on both: starting price (Free), free tier (Yes), user rating (Not yet rated), category (Browser Extensions).

What each one covers

Drawn from each product's published feature list. An absence here means we hold no record of it - not that the product lacks it.

Only in Greasemonkey

  • Userscript execution
  • Built-in script editor
  • GM. API
  • @resource support
  • Script localisation
  • Firefox for Android

Only in JSON Viewer

  • JSON formatting
  • Syntax highlighting
  • Tree view
  • Search functionality
  • Chrome support
  • Firefox support
  • Edge support

What people use each for

The jobs each tool is most often brought in to do.

Greasemonkey

  • Restyling or de-cluttering a site you use dailynot JSON Viewer
  • Automating a repetitive action on a web applicationnot JSON Viewer
  • Adding a missing feature to a site you do not controlnot JSON Viewer
  • Running userscripts on Firefox for Androidnot JSON Viewer
  • Writing and testing your own scripts in the browsernot JSON Viewer

JSON Viewer

No use cases recorded yet. See the JSON Viewer review.

Where each one falls short

Documented limitations, not opinions. Every one is a constraint you would hit in normal use.

Greasemonkey

  • Firefox only. There is no Chrome, Edge or Safari build and there never has been.
  • Its API diverged from the Tampermonkey conventions most shared scripts are written against, so a script from a sharing site may need adjusting to run.
  • The dashboard is plainer than Tampermonkey's, with no diff view when a script updates itself.
  • No cloud sync of the kind Tampermonkey and Violentmonkey offer; moving machines means exporting.
  • A userscript manager can read and rewrite every page you visit, so the security of the arrangement depends entirely on the scripts you choose to install.

JSON Viewer

  • The project is MIT licensed open source code hosted on GitHub with no vendor and no paid tier

Pricing, plan by plan

Greasemonkey

Free
  • Open sourceFree
    • Unlimited scripts
    • Built-in editor
    • No account required

JSON Viewer

Free
  • FreeFree
    • Syntax highlighting
    • Collapsible tree
    • Search

Which should you pick?

Choose Greasemonkey if

  • You need userscript execution.
  • You want to start without paying.
  • You work on Firefox.
  • You also want built-in script editor.
Greasemonkey review

Choose JSON Viewer if

  • You need json formatting.
  • You want to start without paying.
  • You work on Chrome, Firefox, Edge.
  • You also want syntax highlighting.
JSON Viewer review

Questions people ask

Is Greasemonkey or JSON Viewer better?
Neither clearly leads. Greasemonkey starts at Free and JSON Viewer at Free, and user ratings are close enough to be indistinguishable. Choose on capability and platform support.
Which is cheaper, Greasemonkey or JSON Viewer?
Greasemonkey starts at Free and JSON Viewer at Free.
Does Greasemonkey or JSON Viewer run on more platforms?
Greasemonkey runs on Firefox. JSON Viewer runs on Chrome, Firefox, Edge.
Can I use Greasemonkey for free?
Both have a free tier, so you can try either at no cost before committing.
What is Greasemonkey best used for?
Greasemonkey is most often used for restyling or de-cluttering a site you use daily, automating a repetitive action on a web application, adding a missing feature to a site you do not control, running userscripts on firefox for android. Of those, restyling or de-cluttering a site you use daily and automating a repetitive action on a web application are not what JSON Viewer is typically brought in for.
What can Greasemonkey do that JSON Viewer cannot?
Greasemonkey covers Userscript execution, Built-in script editor, GM. API, @resource support. JSON Viewer covers JSON formatting, Syntax highlighting, Tree view, Search functionality.

Answered from the vendors’ own pages

Greasemonkey: Is Greasemonkey still maintained?

Yes. Version 4.14 was released on 2 June 2026, and the project has an active repository, bug tracker and discussion groups.

Source
Greasemonkey: Does Greasemonkey work on Chrome?

No. It is a Firefox extension and has never shipped for Chrome. Violentmonkey and Tampermonkey are the equivalents there.

Source
Greasemonkey: Will Tampermonkey scripts run in Greasemonkey?

Often, but not always. Greasemonkey's API diverged from the conventions most shared scripts are written against, so a script may need its header or its GM calls adjusted.

Source
Greasemonkey: Does Greasemonkey run on mobile?

On Firefox for Android, from version 4.12. There is no iOS build, because Firefox on iOS cannot load extensions of this kind.

Source
Greasemonkey: What is the GM API?

The set of functions a userscript manager exposes to scripts, named after Greasemonkey, which defined it. Greasemonkey supports the promise-based GM. form including GM.xmlHttpRequest and GM.registerMenuCommand.

Source
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