Did you check addons.opera.com? There is one called JSONViewer.

Answer from Erik Dahlström on Stack Overflow
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Opera
addons.opera.com › en › extensions › details › json-lite
JSON Lite extension - Opera add-ons
These extensions and wallpapers are made for the Opera browser. ... Features: - Format JSON and JSONP responses - Select and format JSON on every page - Collapsible arrays, objects and long values - Collapse all childs with Ctrl(Command) + Click - Collapse property also on all sibling items with Alt(Option) + Click - Count items and properties in a collection - Show collection sizes - Do its best to show large (10MB+) JSON files - Do its best to show invalid JSON files - Do not sort objects with numeric keys - Do not round large numbers - "Save as..." saves the original JSON document - Select and copy a working JSON from the formatted JSON
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Opera
addons.opera.com › en › extensions › details › json-beautifier
JSON Beautifier extension - Opera add-ons
This extension monitors JSON pages and converts them into a human-readable object. You can view, edit, search through values and keys. You can even change the format of a key or drag it into a new place.
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Opera
addons.opera.com › en › extensions › details › json-formatter-beautifier
JSON Formatter & Beautifier extension - Opera add-ons
JSON Formatter & Beautifier that takes raw, unformatted JSON data and transforms it into a well-structured and indented format. This transformation makes it significantly easier for developers, data analysts, and other users to comprehend the ...
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GitHub
github.com › tulios › json-viewer › issues › 163
Doesn't trigger on Opera when installed through compatibility layer - possible fixes? · Issue #163 · tulios/json-viewer
There is Chrome extensions compatibility layer add-on for Opera, which allow installation of Chrome extensions on Opera, as name suggests. However although JSON Viewer installs just fine on Opera, and options page works perfectly, it doesn't ...
Published   Aug 07, 2017
Author   xZero707
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Opera
forums.opera.com › topic › 66786 › is-it-possible-to-disable-the-default-json-viewer
Is it possible to disable the default JSON viewer? | Opera forums
October 6, 2023 - If it is not possible to disable it is there any way for an extension to take precedence over the default viewer? ... @leocg Yes it does, open https://jsonplaceholder.typicode.com/posts in Opera and you'll see a page that looks like the screenshot I posted.
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WebExtension.ORG
webextension.org › listing › json-beautifier.html
Json Beautifier :: WebExtension.ORG
Not only can the extension beautify server files, but it can also beautify local JSON files (starting from version 0.1.3). Please make sure that the "allow access to file URLs" option is enabled for this extension on the "chrome://extensions" page. This step is necessary if you are on a Chromium-based browser such as Chrome, Edge, or Opera.
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GitHub
github.com › pd4d10 › json-viewer
GitHub - pd4d10/json-viewer: Port of Firefox's JSON Viewer for Chromium-based Browsers
Port of Firefox's JSON Viewer for Chrome and Opera · Install it from Chrome Web Store · Opera users could use this extension: Install Chrome Extensions · Try https://httpbin.org/headers after installation · Open Allow access to file URLs to make file:/// work ·
Starred by 249 users
Forked by 32 users
Languages   JavaScript 69.4% | TypeScript 29.9% | CSS 0.7%
Find elsewhere
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Opera
addons.opera.com › en › extensions › details › jsonviewer
We cannot provide a description for this page right now
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Stack Overflow
stackoverflow.com › questions › 11118967 › how-to-view-json-objects-in-opera-in-webdriver-automation-testsjava
How to view json objects in opera in WebDriver Automation Tests(java) - Stack Overflow
I executed selenium webdriver tests for nodejs projects am unable to view the json objects in opera(11.64).I get a modal box(download file) asking to save the file but even after downloaling it shows "No registered application for this extension." Any idea on this. Manually I can view it when I added json viewer extension or JsonHero extention.But I face this issue only when I execute the tests(webdriver-version 2.21.0).
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Jsonview
jsonview.com
JSONView - View JSON in Firefox and Chrome | BenHollis.net
A Firefox and Chrome extension that pretty-prints JSON data.
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Chrome Web Store
chromewebstore.google.com › detail › json-viewer-pro › eifflpmocdbdmepbjaopkkhbfmdgijcc
JSON Viewer Pro - Chrome Web Store
A completely free extension to visualise JSON response in awesome Tree and Chart view with great user experience and options. It…
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Mozilla Add-ons
addons.mozilla.org › en-US › firefox › addon › jsonview
JSONView – Get this Extension for 🦊 Firefox (en-US)
May 17, 2025 - JSONView was built to display JSON documents in an easy to read format, which is still nice if you don't like the default viewer. The document is formatted, highlighted, and arrays and objects can be collapsed.
Rating: 4.1 ​ - ​ 81 votes
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Chrome Web Store
chromewebstore.google.com › detail › json-formatter › gpmodmeblccallcadopbcoeoejepgpnb
JSON Formatter - Chrome Web Store
To make JSON Formatter work properly on all kinds of sites, in the extension permissions, change "Allow this extension to read and change all your data on websites you visit" from "On Click" to "On all sites," if not already set.
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DEV Community
dev.to › rezmoss › json-viewer-plus-the-last-json-extension-youll-ever-need-4mab
JSON Viewer Plus: The Last JSON Extension You'll Ever Need - DEV Community
November 20, 2024 - Hey fellow developers! Let me tell you a story about why I created JSON Viewer Plus. Like many of... Tagged with chrome, extensions, webdev, json.
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Jsongrid
jsongrid.com
JsonGrid - All-In-One JSON Solution
🚀 New! JSONGrid Web Inspector Try our new Chrome DevTools extension to view JSON responses in JSONGrid.
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Opera
addons.opera.com › es-419 › search
Resultados de búsqueda - Complementos de Opera
Ver todo · x · Mostrar los objetos JSON transformándolos en HTML resaltado y editable por sintaxis para validarlos, formatearlos y guardarlos. Puntuación: Número total de puntuaciones:29 · Fast JSON viewer - highlights, shows items count/size, ...