Every developer accumulates a set of small utilities they reach for without thinking. Decode a token to see why auth is failing. Pretty-print a minified API response. Work out what 0 17 * * 5 actually means before it fires in production.
None of these are hard problems. They are just friction, and friction repeated forty times a week adds up. Here are thirteen browser tools worth keeping one tab away, grouped by the problem they solve.
Working with data formats
1. JSON Formatter
The most-reached-for tool in any developer's kit. API responses arrive minified, and a minified payload with deep nesting is unreadable. JSON Formatter indents it and validates the structure at the same time.
That validation is the underrated part. When an API returns something your parser rejects, the fastest way to find out why is to paste it into a formatter and let it point at the character where things went wrong — usually a trailing comma, a single quote where JSON demands double, or an unescaped newline inside a string.
2. CSV to JSON and JSON to CSV
The most common data-wrangling task there is. Someone sends a spreadsheet export and your import expects JSON, or you have API output that a colleague wants in Excel. CSV to JSON and JSON to CSV handle both directions, including the parts people get wrong by hand — quoted fields containing commas, embedded newlines, inconsistent headers.
3. YAML and XML formatters
YAML's indentation sensitivity makes it uniquely easy to break in ways that are invisible to the eye. A tab where spaces were expected, or a key indented one space too far, changes the structure silently. YAML Formatter catches it before your pipeline does.
XML Formatter earns its place whenever you touch SOAP endpoints, sitemaps or configuration files — all of which are still very much alive regardless of how they are regarded.
Debugging what is actually happening
4. JWT Decoder
When authentication fails, the token usually explains it. JWT Decoder splits a token into header, payload and signature so you can read the claims directly.
Nine times out of ten the answer is in exp — the token expired. The rest are usually a wrong aud or iss, a missing scope, or a clock-skew problem where nbf is slightly in the future.
Worth understanding: the header and payload of a JWT are Base64-encoded, not encrypted. Anyone holding the token can read them. That is by design, and it is exactly why you should never put anything sensitive in a JWT payload. Decoding one does not verify it — verification requires checking the signature against the key.
5. API Tester
Before you write client code, confirm the endpoint does what the documentation claims. API Tester lets you fire a request with custom headers and a body, and inspect the raw response.
This separates two very different bugs: the API is wrong, or your code is wrong. Establishing which one you are dealing with first saves an enormous amount of time.
6. HTTP Status reference
Everyone knows 404 and 500. The useful ones are the codes you meet rarely and have to look up every time — 422 versus 400, when 409 is right, what 429 implies about retrying. HTTP Status is a quick reference for choosing the correct code rather than defaulting to 400 for everything.
7. Webhook Tester
Webhooks are difficult to debug because the sender is out of your control and the receiver is often behind a firewall. Webhook Tester gives you an endpoint that captures whatever arrives, so you can see the actual payload and headers a provider sends — which is frequently not quite what their documentation describes.
Patterns, schedules and identifiers
8. Regex Tester
Regular expressions are write-once, debug-forever. Regex Tester highlights matches live as you type, which turns a guessing game into an iterative one.
The real value is testing against the inputs that break things: the empty string, a string with a newline, one with Unicode, one that is nearly a match. Most regex bugs in production are not "it does not match" — they are "it matches something it should not".
9. Cron Generator and Parser
Cron syntax is terse and unforgiving, and the cost of a mistake is asymmetric: a job that runs too often is noisy, but a job that silently never runs can go unnoticed for months.
Cron Generator builds an expression from plain requirements, and Cron Parser translates an existing one back into English. Before changing a schedule in a live system, parsing it first is a habit worth having.
10. Unix Timestamp Converter
Logs and databases store epoch seconds; humans do not read epoch seconds. Unix Timestamp converts in both directions.
It is also how you catch the classic seconds-versus-milliseconds bug — if a date lands in 1970, you passed seconds where milliseconds were expected, or the value was truncated somewhere upstream.
11. UUID Generator
UUID Generator produces identifiers for test fixtures, seed data and migrations. Useful when you need a valid-format identifier immediately rather than booting an application to generate one.
Frontend and delivery
12. Code Beautifier and minifiers
Code Beautifier makes minified source readable, which is how you investigate a bug in a third-party bundle you do not have the source for.
Going the other way, CSS Minifier and JS Minifier are handy for one-off assets that are not part of a build pipeline — a landing page, an embedded widget, an email template.
13. Color Contrast checker
Accessibility requirements are specific: WCAG AA wants a contrast ratio of at least 4.5:1 for normal text and 3:1 for large text. Eyeballing it does not work, particularly with mid-tone greys, which are exactly where designs tend to fail.
Color Contrast gives you the ratio and pass/fail against each level. Grey-on-white body text and white-on-brand-colour buttons are the two places this catches problems most often.
Honourable mentions
- Fake Data Generator — realistic test records without using real customer data in a development database.
- Diff Viewer — compare two config files or API responses when the difference is one character somewhere in four hundred lines.
- SQL Formatter — for the inherited 200-line query written as a single line.
- Number Base Converter — hex, binary, decimal, octal. Permissions, colour values, bitmasks.
- Chmod Calculator — because nobody remembers whether it is 644 or 755 without thinking.
- DNS Propagation Checker — after a DNS change, the only useful question is whether it has propagated where your users are, not where you are.
- Website Status Checker — settles "is it down, or is it just me" in three seconds.
A note on pasting things into web tools
Developer tools handle sensitive material routinely — production tokens, customer records, internal configuration. It is worth a moment's thought about where that data goes.
Tools that run entirely in your browser process the input on your own machine; nothing is transmitted. Tools that need a server — anything checking DNS, fetching a URL or resolving an IP — necessarily send something, because the work cannot happen locally.
The practical habit: before pasting a real production JWT or a live API key into any online tool, consider whether you could use an expired token or a redacted sample instead. Usually you can, and it costs nothing.
All the tools above are free to use on ZeeSharp, with no sign-up needed to try them.