Tools Viewer

All Tools - Best free online tools for developers

ToolsViewer brings together some of the best free online tools for developers in one place. Filter by topic, browse a category, or search by name. No signup online tools, ever.

Built to Be the Best Free Online Tools for Developers

ToolsViewer was built around a clear goal: to offer some of the best free online tools for developers without requiring payment or registration. There is no account to create, no card to add, and no upgrade prompts interrupting your work. Open a tool, complete the task, and move on.

Every tool on this page runs client-side wherever possible, which means your HTML, your JSON, your regex patterns, and your email drafts stay on your device unless you choose to export or share them. That is the reasoning behind a no signup online tools approach - fewer steps between you and the result you need.

Tools on this page are organized into four categories: Viewers, Formatters, Converters, and Testers. Use the search box if you already know a tool's name, select a popular filter if you are searching by task, or browse each category to see what is available. New tools are added to this free online tools directory on an ongoing basis.

Tools
40+
Groups
19+
Price
Free
Account
Not required

Popular filters:

YAML1

Moving configuration between YAML and JSON is a routine task, and a small formatting error can cause big problems. These tools convert your data quickly in the browser, so your files stay on your device.

JSON11

Working with JSON means constantly checking syntax, fixing small mistakes, and reshaping data for other tools. These JSON tools let you validate, repair, compare, and convert it right in your browser, with nothing sent to a server.

HTML22

HTML is easy to break when you’re constantly editing, testing, or moving markup between tools. These HTML tools help you view, format, validate, and work with your code directly in the browser, without the need to upload it to third-party services.

Viewers3

Nothing is worse than sending an email or pushing a page live only to find a rendering bug five minutes later. The two tools in this group let you preview your work exactly as it will appear - in an inbox, in a browser, or on a phone screen - before anyone else sees it.

Formatters4

Messy JSON and broken XML slow everyone down. These two formatters catch syntax errors instantly, pretty-print anything you paste, and turn cramped, unreadable data into something a human - or the next tool in your pipeline - can actually use.

Converters20

Sometimes the format you have is not the format you need. These converters move data between JSON and XML in a single step, which removes the need to copy data into third-party sites that may store it on their own servers.

Testers2

Regular expressions are powerful and famously easy to get wrong. This tool turns cryptic patterns into something you can actually see, test, and fix - without opening ten browser tabs just to look up syntax.

Validators3

A missing closing tag or nested element in the wrong place can break a layout in production. These validators check HTML structure in your browser so you can fix issues early - without uploading files to a third-party checker that keeps a copy of your markup.

Extractors2

Sometimes you do not need the whole page - you need the table, the tree, or the structured bits buried inside HTML. These extractors pull usable data out of markup on your device so you can move it into spreadsheets, APIs, or the next step in your workflow.

Decoders1

HTML entities and escaped strings are fine for machines and a headache for humans. These decoders unescape &, <, and the rest back into plain text in your browser - private, fast, and without pasting sensitive copy into a random online decoder.

Encoders1

Dropping raw text into HTML is how broken pages and XSS headaches start. These encoders escape the characters that need escaping so your content can sit safely inside markup - processed locally, with nothing uploaded to someone else's server.

Escapers1

Quotes, ampersands, and angle brackets mean one thing in prose and another in HTML. These escapers handle the special characters that break attributes and elements, so your snippets stay valid when you paste them into templates or emails.

Parsers1

Paste HTML and get a clear read on element counts, depth, and document stats without spinning up a local project. These parsers run in your browser so you can inspect structure quickly when you are debugging, documenting, or cleaning up inherited markup.

Editors3

Not every change needs a full IDE. These editors let you tweak HTML, email, JSON, or XML with live tools in the same tab - free, no signup, and designed so your drafts stay on your device while you work.

Diff Checker2

Guessing what changed between two HTML revisions wastes time and misses regressions. This diff checker snapshots a baseline, highlights added and removed lines, and keeps the comparison in your browser so you can review markup changes before you commit or send.

Minifiers2

Comments and extra whitespace inflate HTML that has to load fast. These minifiers strip the noise for delivery while leaving the work on your device - handy when you want smaller output without trusting a minify-as-a-service with your source.

Structure1

Nested sections, orphaned nodes, and deep trees are hard to see in a flat code view. These structure tools open a DOM-style outline of your HTML so you can navigate hierarchy, spot odd nesting, and understand the page shape before you refactor.

Inspectors3

When something looks wrong, you need details - matches, outline nodes, or rendered context - not another download. These inspectors surface what is going on inside your markup or pattern so you can diagnose issues privately in the browser.

Compressors2

Every extra byte of whitespace is another millisecond on a slow connection. These compressors tighten HTML for delivery in your browser, so you can ship leaner markup without routing your content through an external compression service.

FAQ

Why does my JSON file show a syntax error when I try to use it?
JSON syntax errors are almost always caused by a trailing comma, an unquoted key, or a missing bracket. Open JSON Formatter & Converter, paste your file, and it highlights the exact line where the format breaks, so you can fix it in seconds instead of scanning the whole file by hand. This is especially useful when working with large configuration files or API responses, where a single misplaced character can be difficult to spot manually.
How can I preview an HTML email before sending it to a client or subscriber list?
Use HTML Email Builder to paste your HTML and preview it as it would appear in Gmail, Outlook, Apple Mail, and Yahoo. This lets you catch layout breaks, broken images, or dark mode issues before the email reaches an inbox.
How do I convert an XML file into JSON without writing a script?
Open XML Formatter & Converter, paste or upload your XML, and use the built-in convert option to turn it into JSON instantly. This works well for API responses, configuration files, and SOAP or WSDL data that need to move into a JSON-based system.
Why is my regular expression not matching the text I expect?
A small mistake, such as an unescaped special character or the wrong quantifier, is the most common reason a pattern fails. RegEx Visualizer & Explainer highlights each match live as you type and steps through your pattern piece by piece, so you can see exactly where it stops matching.
How can I check if my HTML code will display correctly across different browsers?
HTML Viewer renders your HTML, CSS, and JavaScript live as you edit, so you can preview layout, spacing, and structure before publishing. Catch broken tags or unclosed elements early, and compare how the same markup looks as you tweak it. This is particularly helpful when a page looks correct in one browser but breaks in another, since small markup errors are usually the underlying cause.
What is the easiest way to check an email for dark mode display issues?
HTML Email Builder includes a dark mode toggle that simulates how an HTML email will look when a recipient's email client switches to dark mode, which helps you catch invisible text or clashing background colours before sending a campaign.
How do I validate XML data before importing it into another system?
Paste your XML into XML Formatter & Converter and use the validate option to check for structural errors, unclosed tags, or invalid characters. This is useful before importing SOAP, WSDL, or configuration files into another application.
Can I convert JSON data into CSV or XML for a spreadsheet or another system?
Yes. JSON Formatter & Converter supports converting JSON into XML and CSV formats directly in your browser, which is useful when moving API data into a spreadsheet or a system that expects a different format.
How do I debug a regex pattern that only fails on certain inputs?
Use the step debugger inside RegEx Visualizer & Explainer to walk through your pattern against different sample inputs. It shows which part of the pattern matches and which part fails, which is faster than testing by trial and error in a code editor.
Are these tools free to use, and do I need to create an account?
Yes. Every tool on this page is part of a set of the best free online tools for developers, with no signup, no account, and no payment required to use the core features.