The Browser Tools Every Developer Actually Needs in 2026

At some point in your career you develop a set of tools you reach for without thinking. Not because you planned it. Because you got burned enough times by the alternatives.

You pasted a JWT into a random decoder site and only afterward wondered whether it just sent your token to a server. You formatted JSON in a tool that crashed on a 2MB payload. You tested a regex in a browser console by writing a throwaway script, running it, realising the flags were wrong, and running it again. You converted a Unix timestamp by asking a language model, which gave you the wrong timezone.

These are all solved problems. The tools exist. The issue is knowing which ones are worth keeping.

This is the list that belongs in your bookmarks bar. Tools that developers genuinely reach for while writing code, debugging APIs, and reviewing pull requests. All run entirely in your browser. No data leaves your device.

Quick Reference

Data and Code

The tools you'll open every day when working with API responses, config files, or query logic.

JSON Formatter and Validator

Raw API responses are unreadable on a single line. The JSON Formatter and Validator fixes that with properly indented, syntax-highlighted output and error messages that pinpoint the exact position of the problem when input is invalid.

It catches things most formatters miss: numbers that exceed JavaScript's safe integer limit (the Twitter ID precision bug), duplicate keys, and JSONC trailing commas that standard parsers reject. When an API response looks wrong and you can't figure out why, this is the first tab to open.

SQL Formatter

A 40-line query as a single string with mixed-case keywords isn't a code review. It's a puzzle. The SQL Formatter reformats SQL across MySQL, PostgreSQL, SQLite, and T-SQL with consistent keyword casing, indented subqueries, and aligned join conditions. Paste the query, format it, then ask for review. Most WHERE clause logic bugs get caught at review time when the query is actually readable.

Regex Tester

Regex is easy to write and easy to get wrong. The Regex Tester shows matches in real time, highlights every capture group, and lets you test against multiple inputs at once. Test against adversarial inputs, not just the happy path. Nested quantifiers can cause catastrophic backtracking, and you won't find out until it's already a production problem.

Encoding and Decoding

Both tools here process everything locally. Credentials and sensitive payloads never leave your browser.

Base64 Encoder and Decoder

Base64 shows up constantly. JWT tokens are three Base64URL-encoded strings joined by dots. HTTP Basic Auth headers encode credentials in Base64. CSS data URIs embed images inline as Base64. Most developers use it every day without realising it.

The Base64 Encoder and Decoder handles both standard Base64 and the URL-safe variant, Base64URL. Mixing them causes silent decoding failures, so the variant matters. Got an opaque token back from an API? Decode it here before building any logic on top of it.

URL Encoder and Decoder

A space in a query parameter becomes %20 or a plus sign depending on context, and the difference can break things. An unencoded ampersand splits the query string at the wrong position. An unencoded hash terminates the path before the server sees the query.

The URL Encoder and Decoder encodes individual components and decodes percent-encoded strings back to readable form. Reach for it when you're constructing query strings manually, debugging a redirect that's stripping parameters, or reading a URL that's been encoded multiple times by an automated system.

Auth and Identity

Two tools for authentication work that backend and full-stack developers deal with constantly.

JWT Decoder

Three Base64URL strings separated by dots. That's a JWT. The header holds the algorithm and key ID. The payload holds every claim: expiry, issuer, subject, audience, and any custom fields your auth service adds.

The JWT Decoder decodes all three sections in the browser without sending the token anywhere. That matters when the payload contains user data or credentials. When auth is broken in production and the error is generic, decoding the token usually tells you the cause in under a minute. Is it expired? Does the issuer have a trailing slash? Does the audience not match? The payload has the answers.

UUID and ULID Generator

UUID v4 is random and universally supported but fragments B-tree indexes at scale. UUID v7 fixes that with a timestamp prefix that keeps sequential inserts sequential. ULID is 26 characters, millisecond-precise, and sorts correctly as a plain string without a native database type.

The UUID and ULID Generator produces all three formats with bulk generation for when you need a set of IDs for a fixture, a migration, or a test run. It's faster than dropping into a REPL.

Debugging and Inspection

Three tools for the constant work of reading things: timestamps in logs, hashes in checksums, Markdown in documentation.

Unix Timestamp Converter

Timestamps in logs and API responses are almost always Unix format: seconds or milliseconds since January 1, 1970 UTC. The Unix Timestamp Converter converts in both directions, handles seconds and milliseconds automatically, and shows UTC and local time side by side.

When events in a distributed system look out of order and you're working out the real timeline, paste the timestamps here. Don't write a throwaway script. Don't ask an assistant that'll silently assume the wrong timezone.

Hash Generator

MD5 and SHA-256 are the wrong choice for password storage. Use bcrypt, scrypt, or Argon2 for that. For everything else, hashing is exactly right: verifying a downloaded file against a published checksum, generating a content fingerprint for deduplication, producing a compact cache key from request parameters, implementing Subresource Integrity for CDN assets.

The Hash Generator computes MD5, SHA-1, SHA-256, and SHA-512 entirely in the browser. Paste the content, get the hash, compare or store.

Markdown Preview

Every README and pull request description you write gets rendered as Markdown before anyone reads it. The rendering varies by platform. A table with correct syntax can wrap unreadably. A code block without a language hint loses syntax highlighting. A task list won't render if the platform doesn't support GFM.

The Markdown Preview renders exactly as GitHub would, tables, strikethrough, and task list checkboxes included. Write locally, paste here, verify the output, push. Ten seconds and no commit just to fix a broken table.

Converting and Optimizing

Data rarely arrives in the shape you need it in. These three tools handle the unglamorous work of turning one format into another without losing anything along the way.

CSV to JSON Converter

A product manager exports a spreadsheet. You need it as JSON to seed a test database or feed a script. The CSV to JSON Converter parses the file with a configurable delimiter (comma, semicolon, tab, or pipe) and converts numbers and booleans to their real types instead of leaving everything as quoted strings.

It also runs the other direction. Flatten a JSON array back into CSV when a client wants "the data in Excel," which happens more often than any API design would suggest.

JSON to TOON Converter

LLM APIs charge per token, and a JSON array of a thousand near-identical objects repeats every key name a thousand times. The JSON to TOON Converter rewrites uniform arrays into a compact tabular format that an LLM reads just as well as JSON, at roughly 40% fewer tokens.

Paste a database query result or an API response before it goes into a prompt. If the array is uniform, the token count drops immediately, and the conversion round-trips back to identical JSON.

SVG Optimizer

An icon exported from Figma or Illustrator carries editor metadata that never reaches the screen: layer names, comments, unused namespaces, six decimal places of path precision nobody asked for. The SVG Optimizer strips all of it and typically cuts file size by 40 to 70%.

Run it before committing any exported SVG to a repository, especially icon sets and logos that get requested on every page load.

Scheduling and Comparing

Cron Expression Builder

0 9 * * 1-5 runs at 9 AM on weekdays. Reading that at a glance is a skill most people never quite trust themselves with, so the wrong expression ships and a job runs every minute instead of every morning. The Cron Expression Builder translates the expression into plain English and previews the next five run times before it goes anywhere near a crontab or a GitHub Actions workflow.

Text and Code Diff

Not every comparison is a JSON diff. Config files, Dockerfiles, and prose all need a plain line-by-line or word-by-word comparison instead of structural parsing. The Text and Code Diff tool highlights additions and removals with the same Myers diff algorithm git uses, and switches to word-level diffing for prose where line-level highlighting is too coarse.

The Real Cost of Searching Every Day

Every tool on this list solves a problem you'll hit this week.

Searching for a JSON formatter four times a week takes maybe thirty seconds each time. That's roughly two hours a year on one tool. Across ten tools it's a week of work gone to friction that doesn't need to exist.

All of these are at developertoolkit.dev. Nothing is sent to a server. No sign-up, no rate limit, no email prompt before you can paste.

Bookmark it. The next time you open a new tab looking for a formatter, it'll already be there.