Installing a tool for a quick one-off task is a bad trade: 10 minutes finding the right package, another 5 configuring it, and then you never touch it again. Every tool below runs in the browser. No install, no account, nothing stored on a server. Paste your input, get your output.
1. JSON Formatter & Validator
Paste a raw JSON blob and the formatter indents it with 2-space or 4-space nesting, your choice. Invalid JSON doesn't fail silently: you get the exact line and column where the syntax breaks. Useful when an API response comes back minified and you need to read it, or when a config file refuses to parse and you can't spot the missing comma.
Everything runs in the browser. The JSON never leaves your machine. Try the JSON Formatter & Validator.
2. JWT Decoder
Paste a token and the decoder splits it into its three parts: header, payload, and signature. You see the algorithm, the claims (sub, exp, iat, and any custom ones), and the expiry as a readable timestamp rather than a Unix epoch. Nothing is verified — this is a read tool, not an auth tool — but it's exactly what you need when debugging an auth issue and you want to know what's actually inside the token you're holding. Client-side, nothing stored. Try the JWT Decoder.
3. Regex Tester
Write a pattern, paste your test string, and every match highlights immediately. Supports the standard flags: g for global, i for case-insensitive, m for multiline. If your pattern has capture groups, those show separately. The feedback is instant — no submit button, no waiting. Browser-side only. Try the Regex Tester.
4. UUID Generator
Generates RFC 4122 version 4 UUIDs: random, 128-bit, formatted as xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx. You can generate up to 100 at once and copy the full list with one click. Useful for seeding a database, generating test fixtures, or anywhere you need unique IDs without hitting a service. Client-side randomness, nothing logged. Try the UUID Generator.
5. Hash Generator
Type or paste any text and get its MD5, SHA-1, SHA-256, and SHA-512 digests simultaneously. All four update as you type. The practical use case is usually verifying a file checksum or checking whether two strings produce the same hash — the kind of thing where you just need the output fast, not a library integration. Everything runs client-side. Try the Hash Generator.
6. Base64 Encoder / Decoder
Encodes text to Base64 or decodes it back. There's a URL-safe mode that replaces + with - and / with _, which matters when the Base64 string ends up inside a URL or a JWT. Common use: encoding credentials for an HTTP Basic auth header, or decoding an email attachment that arrived as Base64 text. Client-side. Try the Base64 Encoder / Decoder.
7. URL Encoder / Decoder
Percent-encodes special characters so they're safe inside a URL, or decodes a percent-encoded string back to plain text. The tool handles both directions: encode a raw query parameter value before adding it to a URL, or decode an incoming URL string to read what it actually says. Spaces become %20, ampersands become %26, and so on. Client-side. Try the URL Encoder / Decoder.
8. Text Diff Checker
Paste two blocks of text and the tool shows exactly what changed: additions in green, deletions in red, line by line. Useful for comparing two versions of a config file, spotting what changed between two API responses, or reviewing a quick edit before committing it. No file upload needed — paste directly. Client-side. Try the Text Diff Checker.
9. Unix Timestamp Converter
Converts in both directions: a Unix epoch (seconds or milliseconds) to a human-readable date and time, or a date to its epoch value. The output includes both UTC and your local timezone. Epoch timestamps show up everywhere in logs, API responses, and JWT exp fields — this is the fastest way to check what one actually means without writing a one-liner in your terminal. Client-side. Try the Unix Timestamp Converter.
10. Cron Expression Builder
Build a cron schedule visually: pick minutes, hours, days, months, and weekdays through a UI, and the expression updates live. The tool also shows the next 10 fire times in plain datetime format so you can confirm the schedule does what you think it does before dropping it into a crontab or a scheduler config. Client-side. Try the Cron Expression Builder.
These are ten of the most-used tools in the developer section at at-use.com. The full collection covers more ground: formatters, converters, network tools, and text utilities — all free, all browser-side.