Every developer keeps a handful of small utilities within arm’s reach — the ones you reach for a dozen times a day without thinking. This is a curated checklist of ten free, browser-based tools that cover the most common day-to-day tasks. All of them run locally in your browser, so nothing you paste is uploaded to a server.
What “working correctly” actually looks like. Every tool in this checklist has a published, verified output on its own page, so you can tell a broken tool from a correct one. Three you can check against anything else:
hellohashes to5d41402abc4b2a76b9719d911017c592in MD5; a trailing comma in JSON produces Expected double-quoted property name in JSON at position 7 (line 1 column 8); and our colour picker extracts all six colours of the illustration we drew ourselves. Those are on the Conversion Lab and the individual tool pages — the point of a checklist is that each item is checkable.
1. JSON formatter
Machine-generated JSON is often crammed into one unreadable line. A JSON formatter beautifies it into a clear indented structure, minifies it back down for transport, and validates the syntax so you catch a stray comma before your code does.
What to look for: does it tell you where the error is? Ours reports a trailing comma as ✗ JSON syntax error: Expected double-quoted property name in JSON at position 7 (line 1 column 8) [L1:8] — the position matters more than the wording, because parsers report where they gave up, not where you slipped.
2. Base64 encoder / decoder
When you need to carry binary or special characters through a text-only channel — email, JSON, data URIs, JWTs — Base64 is the answer. A good Base64 tool handles full UTF-8 (so Chinese, Japanese and emoji survive the round trip) and offers a URL-safe mode.
A quick check that an encoder is doing UTF-8 properly: Hello, World! must come back as SGVsbG8sIFdvcmxkIQ==. If a tool gives you something shorter, it dropped the exclamation mark or mangled the byte length.
3. Hash generator
Verifying a downloaded file, comparing two blobs of text, or learning how hashing works? A hash generator that uses the browser’s native Web Crypto API gives you SHA-256 and SHA-512 instantly, without sending your input anywhere.
Verify a hash tool against a value you can reproduce offline. hell0 under MD5 is 73b43f17232b391b9123adf40c1b65dd — one character away from hello, and nothing in common with its digest, which is the avalanche property you want to confirm before trusting the tool with a checksum.
4. UUID generator
Need a batch of unique identifiers for database keys or test data? A UUID generator produces RFC 4122 v4 IDs using a cryptographic random source — copy a hundred at once.
The property worth testing is not “does it look random” but “is the format right”. Ours generated 1000 identifiers with 1000/1000 unique, all 36 characters, all with version digit 4.
5. Unix timestamp converter
Logs and APIs love storing time as a Unix timestamp, which humans can’t read at a glance. A timestamp converter turns those numbers into local and UTC dates (and back) and shows a live current timestamp.
The feature that saves the most time is showing local and UTC at once. 1767225600 returns Local: 2026-01-01 08:00:00 UTC: 2026-01-01 00:00:00 on our machine — the two lines differ by the offset, and that difference is where timestamp bugs live.
6. Word counter
Whether you’re writing an essay, tuning an SEO article, or squeezing a post under a character limit, a word counter gives you words, characters, sentences, paragraphs and reading time as you type.
Ask what it counts. A three-sentence English paragraph gave us 33 words, 169 characters and 137 without spaces — three numbers that disagree by design, and a tool that shows only one of them is hiding the disagreement.
7. Case converter
Renaming variables or tidying titles? A case converter switches between camelCase, snake_case, kebab-case, Title Case and more in one click.
Test it with an acronym before you trust it on identifiers. HTTP response code becomes HttpResponseCode in PascalCase and http_response_code in snake_case in ours — the acronym is flattened, which is what most style guides want but is still a decision you should see happen.
8. URL encoder / decoder
Special characters and non-ASCII text break URLs. A URL encoder percent-encodes query parameters correctly and decodes the cryptic %XX strings you copy from an address bar.
The test case that separates a correct encoder from a lazy one is a query string. ?q=x&r=y must come back fully escaped as %3Fq%3Dx%26r%3Dy; a tool that leaves ? or & alone is encoding a value as if it were a whole URL.
9. A diff / text-compare tool
When two files “look identical” but behave differently, a diff tool highlights the exact characters that changed. (Coming soon to our toolbox.)
Check what it does with an inserted line rather than a changed one. Ours returns alpha + beta gamma — one marked line and the neighbours unmarked, which is how you tell a real insert from a change.
10. A regular-expression tester
Regex is powerful and easy to get wrong. A live tester that highlights matches as you type turns trial-and-error into something you can actually reason about. (Coming soon.)
The feature that matters is showing match positions, not just a count. Against <b>bold</b> and <i>it</i>, the lazy pattern <.+?> reports 4 match(es) in ours and lists them as #1"<b>"@0 #2"</b>"@7 #3"<i>"@16 #4"</i>"@21 — the offsets are what let you see that the greedy version swallowed the whole string.
How to choose a good online tool
Not all “free” tools are equal. A few things worth checking:
- Does it run locally? If a tool processes your data in the browser (like the ones above), your input never leaves your device — important for anything sensitive.
- Is it fast? Static, CDN-served tools load instantly and respond without a network round trip.
- Is it honest about its limits? For example, a hash tool that skips MD5 because it’s insecure is telling you something useful.
Bookmark the handful you use most, and you’ll shave a surprising amount of friction off your day. You can find all of the tools above, free and privacy-first, right here on Yunknow Toolbox.