10 Free Online Developer Tools That Save Hours Every Week
Ten free browser-based developer tools for everyday coding tasks. Format JSON, test regex, decode JWTs, generate UUIDs, and much more with no downloads needed.
The Browser as Your Toolbox
Every developer has a shortlist of utility tasks they hit a few times a week. Formatting a mangled JSON response. Testing a regex pattern. Decoding a JWT to check user roles. Generating UUIDs for test data. Converting a Unix timestamp to something a human can actually read.
The traditional approach to each of these involves either installing a standalone app, spinning up a throwaway script, or remembering the right CLI flag for a tool you last used three weeks ago. Each detour costs two to five minutes. Across a workweek, that adds up.
Browser-based tools remove the friction. You open a tab, paste your data, and get the result. No install. No dependency tree. No CLI history to scroll through. The data stays in your browser's memory. The round trip is measured in milliseconds, not in "let me find that script I wrote."
Here are ten browser-based tools that replace the most common small-task detours, with concrete scenarios for each one.
1. JSON Formatter and Validator
You hit an API endpoint that returns a 3,000-character JSON string as one unbroken line. You need to find a specific nested field. Scrolling horizontally through a single-line blob is not a debugging strategy.
The JSON Formatter pretty-prints the response in one click. Indentation reveals the object hierarchy. Nested arrays stop being a wall of brackets and become scannable blocks. Numbers, strings, and nulls each get their own visual space.
Before formatting, run the response through the JSON Validator. It catches syntax errors at the exact line and column. A trailing comma after the last array element. An unquoted key in an object. A missing closing bracket three levels deep. The validator pinpoints each one with an error message and position, so you are not counting brackets by hand.
Real use case: your CI pipeline fails with a JSON parse error from a config file. You copy the config into the validator and it highlights line 47, column 12: a trailing comma. You fix it in 15 seconds instead of staring at the file for five minutes.
Combine the two: validate first to confirm the structure is sound, then format for readability. If you format first, the formatter may produce garbage output from a syntax error, wasting a step.
2. Regex Tester
Writing a regular expression without real-time feedback is a guessing game. You compose a pattern, run it against a test string in a script, get back true or false or a partial match, adjust the pattern, run again. Each iteration takes 20 to 60 seconds depending on your toolchain.
The Regex Tester highlights matches in real time as you type both the pattern and the test string. You see exactly which characters the capture groups are pulling in. You see whether the * is being too greedy or the + is missing edge cases.
Real use case: you need to extract all email addresses from a 200-line log file. You paste the log into the test string area and start building the pattern. You immediately see that \w+@\w+\.\w+ misses addresses with dots in the local part. You add the dot to the character class and see the matches light up. Five iterations in under a minute, versus ten minutes of run-adjust-rerun.
The tester supports common flags: global, case-insensitive, multiline, and dot-all. The match list shows each capture group's value separately, so you can verify that group 1 is the username and group 2 is the domain.
3. JWT Decoder
You are debugging an authentication issue. A JWT appears in a request header, a browser's localStorage entry, or a server log. You need to know: who is this token for, when does it expire, and what roles or permissions does it carry.
The JWT Decoder decodes the header and payload instantly. Paste the token and you see the algorithm used to sign it (HS256, RS256, ES256), the token type, the subject claim, the expiration timestamp, the issued-at time, and any custom claims your auth system attaches.
Real use case: a user reports that they cannot access an admin endpoint. You grab the token from the browser's Network tab, decode it, and check the roles claim. The token only has ["user"], not ["admin"]. Issue identified in 30 seconds. Before you would have pasted the token into a CLI JWT tool, or worse, written a throwaway script to split on dots and base64-decode each segment.
The decoder does not verify the signature. That is the server's job, and it requires the secret key or public key. What the decoder shows you is what anyone who has possession of the token can read. If the exp claim is in the past, the token is expired. If the sub does not match the expected user ID, the token was issued for someone else.
4. Base64 Encoder and Decoder
Base64 encoding shows up everywhere: binary data embedded in JSON payloads, PEM certificate files, data URIs in CSS, and the payload segment of JWTs. You need to encode a string for a test request or decode a payload to inspect its contents.
The Base64 Encoder/Decoder handles standard Base64 and the URL-safe Base64url variant used in JWTs and URL query parameters. Encoding and decoding happen in both directions with a single click.
Real use case: you are writing a test for an API endpoint that expects a Base64-encoded binary payload. You type the raw string into the encoder, copy the Base64 output, and paste it into your test fixture. Done in 10 seconds. Without the tool, you would open a terminal, run echo -n "test data" | base64, copy the output, close the terminal.
The URL-safe variant replaces + with - and / with _ and strips the trailing =. If you are decoding a JWT payload that ends with - and _ characters, switch to Base64url mode. Standard Base64 will produce garbled output.
5. Hash Calculator
You need to verify that a downloaded file matches its published checksum. Or you need to compute the SHA-256 digest of an API response body to include in a request header. Or you want to see what a password's hash looks like for educational purposes (never store raw hashes for passwords in production).
The Hash Calculator supports MD5, SHA-1, SHA-256, and SHA-512. It accepts text input for quick hashing and file input for checksum verification. File hashing runs in the browser using the Web Crypto API. Your file is never uploaded to a server.
Real use case: you download a Docker image tarball that comes with a SHA-256 checksum file. You drag the tarball into the Hash Calculator, select SHA-256, and compare the output against the published checksum. They match. The file was not corrupted or tampered with during download. The verification takes 20 seconds.
For production use, SHA-256 is the minimum. MD5 and SHA-1 are broken for security purposes and should only be used for non-cryptographic integrity checks like detecting accidental corruption.
6. Diff Checker
Two versions of a config file. Two API responses from different environments. Two commits of a function. Spotting the differences by eye is slow, error-prone, and mentally draining.
The Diff Checker does word-level and line-level comparison. Paste the original on the left, the modified version on the right. Added lines appear in one color, removed lines in another, and changed words are highlighted inline within lines.
Real use case: you are reviewing a teammate's pull request that modifies a 400-line YAML config. The PR description says "updated resource limits." You copy the old config and the new config into the Diff Checker. It highlights three changed lines: the CPU limit went from 500m to 1000m, the memory limit from 256Mi to 512Mi, and the replica count from 2 to 3. Review done in one minute.
For JSON responses, run both versions through the JSON Formatter first, then diff the formatted output. This way you get clean structural diffs instead of noise from whitespace differences.
7. UUID Generator
You are writing a database seed script and need 50 unique IDs. Or you are creating a test fixture and need a stable but unique identifier. Or a tracking system expects a UUID as the correlation ID.
The UUID Generator produces UUID v4 values using crypto.getRandomValues(), a cryptographically secure random number generator built into the browser. You can generate a single UUID or batch-generate up to 100 at once.
Real use case: you are preparing a seed script for a Postgres database with 20 sample users. You open the UUID Generator, set the batch count to 20, click generate, and paste the list into your INSERT statement. Ten seconds. The alternative is writing a loop in your seed script or generating them one at a time in a CLI.
UUID v4 is random. For time-ordered UUIDs (v7), you need a different generator. Most use cases in development and testing are fine with v4.
8. Unix Timestamp Converter
A log entry contains the timestamp 1716998400. An API response includes created_at: 1698796800. A database column stores expires: 1735689600. When were these moments?
The Unix Timestamp Converter converts between Unix timestamps and human-readable dates in your local timezone. Paste a timestamp and get back a formatted date with day, month, year, hours, minutes, and seconds. Or pick a date and time from a calendar widget and get the corresponding timestamp.
Real use case: you are investigating an incident and the logs show events at timestamp 1717000000. You convert it and see it was 2:46 AM UTC on May 30, 2024. That lines up with the scheduled maintenance window. Without the converter, you would run date -d @1717000000 in a terminal, or do mental math from the epoch.
The converter also shows the timestamp in milliseconds (JavaScript-style) and the ISO 8601 string format that most APIs expect.
9. SQL Formatter
An ORM debug log or application trace dumps a 200-line SQL query as a single unbroken line. Uppercase and lowercase are mixed. Indentation does not exist. Subqueries blur into JOINs.
The SQL Formatter formats the query with uppercase keywords, consistent indentation, and proper clause alignment. SELECT columns each get their own line. JOIN conditions are indented under the JOIN keyword. WHERE clauses align at the operator. Subqueries are nested visually.
Real use case: your application's slow query log shows a query that took 12 seconds. You copy it from the log, paste it into the SQL Formatter, and now you can actually read it. You spot a missing index on the JOIN column and a Cartesian product from an omitted ON clause. Fix identified in two minutes instead of twenty.
The formatter supports MySQL, PostgreSQL, and standard SQL dialects. For dialect-specific syntax like Postgres's :: cast operator or MySQL's backtick quoting, select the corresponding dialect.
10. Cron Expression Generator
Every CI/CD pipeline schedule, every server crontab, every Kubernetes CronJob uses cron expressions. And every developer has had the experience of staring at 0 */6 * * 1-5 wondering whether that means every six hours on weekdays or something else entirely.
The Cron Generator translates between cron syntax and plain English. Paste 30 9 * * 1-5 and read "At 09:30 AM, Monday through Friday." Or build a schedule from dropdown menus: pick the minute, hour, day of month, month, and day of week, and the tool outputs the cron expression.
Real use case: you are setting up a scheduled pipeline that should run at 3:00 AM on the first day of every month. You select minute 0, hour 3, day of month 1, every month, every day of week. The generator outputs 0 3 1 * *. You paste it into your CI config. No counting asterisks. No second-guessing whether the fields are zero-indexed.
The generator also shows the next five execution times based on the expression, so you can verify that your "every other Friday" schedule actually lands on Fridays.
The Common Thread
All ten tools process data locally in your browser. There are no file uploads to a server, no accounts required, and no session tracking. This matters for two reasons.
First, privacy. Your API responses, JWTs, proprietary source code, and configuration files never leave your machine. You can paste a production token or a client's codebase into any of these tools without exposing it to a third-party service.
Second, speed. Because there is no network round trip for each operation, the tool responds the moment you finish typing or clicking. Formatting a 50 KB JSON payload takes milliseconds, not the two to five seconds a server round trip would add.
Try them now: browse the full tools directory to see every available tool organized by category. Bookmark the ones you reach for weekly. Every tool on the page runs locally in your browser with no account required.