Free AI tools for developers

Zalt.me/tools has 64 free, browser-based tools, and 17 of them are built specifically for developers: JSON to TypeScript/Zod/JSON Schema, a CSV/JSON converter, a Regex Tester, a JWT Decoder, a Mermaid-powered diagram generator, an SQL Formatter, and more. Every one of them runs entirely client-side, no signup, no upload, no ads, free forever. If you write code and you are tired of pasting production data into random ad-filled converter sites, this is the alternative.

I am Mahmoud Zalt, an independent senior AI systems architect. I have shipped production software since 2010, that is 16 years, and I founded Sista AI (sistava.com), where I run autonomous AI agents in production, not demos. I built this tools collection because I needed these exact utilities myself, and I keep maintaining and using it in my own day-to-day work. Nothing here is a marketing gimmick I outsourced, it is what I actually reach for when I am debugging a JWT or reformatting a CSV export.

Why these matter if you write code for a living

Every one of these jobs already has a "free tool" somewhere on the internet. That is exactly the problem. Search "json to typescript" and you land on a page with three ad networks fighting for the same pixel, a countdown before your result renders, and no way to know whether your input is being logged. For a throwaway string that is just annoying. For a JWT from your production auth flow, an API key sitting in a config file, or a CSV export with customer emails in it, it is a real risk you should not be taking for a five-second conversion.

The tools on zalt.me/tools run entirely in your browser. Nothing is uploaded, there is no backend call, no server ever sees what you paste. That means you can drop a real access token into the JWT Decoder or a live database export into the CSV converter without wondering where it just went. It also means they are fast: no round trip, no loading spinner, no third-party script deciding when your result shows up. You paste, you get the answer, you go back to the terminal.

The second reason is context-switching cost. When a task pulls you off your machine, out of your editor and terminal, into a browser tab full of ads, you lose your train of thought. A page that opens instantly, does one job, and gets out of your way keeps you in flow. That is the actual design goal behind every tool here, not an afterthought.

None of this is complicated engineering. Quicktype, Papa Parse, KaTeX, Prettier, and the Web Crypto API already do the hard work, these tools are thin, fast interfaces on top of libraries that already exist. The value is not a clever algorithm, it is removing the friction between you having a piece of data and getting the answer you need from it, without an ad network, a login wall, or a mystery server in between.

Data conversion: JSON, CSV, YAML, Base64

This is the most common developer task there is: turning one data shape into another. These four cover almost everything that comes up in a normal week.

• JSON to TypeScript/Zod/JSON Schema, paste a JSON payload from an API response and get typed interfaces, Zod schemas, or a JSON Schema back instantly, powered by quicktype.
• CSV/JSON converter, move between spreadsheet exports and JSON payloads without hand-writing a parser, built on Papa Parse so it handles quoting and edge cases correctly.
• YAML/JSON converter, useful for Kubernetes manifests, GitHub Actions files, and configs where you need to check the same structure in the other format.
• Base64 encoder/decoder, decode a JWT payload segment, an env var, or an embedded image without opening a REPL.

Also worth knowing about in this category: the Timestamp/Unix converter for turning epoch values into readable dates, and the Number Base Converter for hex, binary, and decimal.

A typical week for me: an API returns a payload I have never seen the shape of, I paste it into the JSON to TypeScript tool and get an interface I can commit straight into the project. A client sends a spreadsheet of product data, it goes through the CSV/JSON converter and comes out as the array my import script expects. Neither of those needs a script of its own, and neither is worth opening an editor for.

Debugging: JWTs, regex, hashes, IDs

The tools you reach for mid-debugging session need to be fast and trustworthy with sensitive input, because that is exactly what you are about to paste into them.

• JWT Decoder, paste a token and see the header, payload, and expiry decoded instantly, without the token ever leaving your machine.
• Regex Tester, test a pattern against real sample strings with live match highlighting before it goes anywhere near your code.
• Hash Generator, generate MD5, SHA-1, SHA-256, and more, for checking file integrity or comparing values quickly.
• UUID/ULID/NanoID generator, generate proper unique IDs on the spot using the Web Crypto API, no need to spin up a script for it.

Round it out with the URL Encoder/Decoder and Query Builder for untangling a messy redirect URL or building a query string by hand.

The JWT Decoder in particular gets more use than anything else in this list. A user reports being logged out unexpectedly, support forwards you their token, and you need to check the expiry and claims in the next thirty seconds, not after copying it into a script and remembering the base64 decode syntax again. Paste, read, close the tab.

Docs and diagrams: Mermaid, LaTeX, SQL, formatting

Writing code is half the job, explaining it is the other half. These are the ones I actually use for documentation, architecture notes, and cleaning up code before it goes into a pull request.

• Diagram from Text, describe a flow or paste Mermaid syntax and get a rendered architecture or sequence diagram for a README or design doc.
• LaTeX Editor, write and preview math notation live, powered by KaTeX, useful for technical docs or academic-adjacent writing.
• SQL Formatter, turn a one-line query dump from a log file into something you can actually read and review.
• Code Formatter, run Prettier on a snippet without opening a project, handy for cleaning up code before pasting it into a ticket or a message to a teammate.

The diagram tool earns its place because most architecture diagrams die in a design tool nobody else on the team has access to. Mermaid syntax is plain text, so the diagram lives in the same pull request as the code it describes, and anyone can update it without learning a new app.

AI-adjacent tooling: tokens, cost, prompts

If you are building anything with LLMs, three more tools save real time and real money.

• AI Tokens Counter, paste a prompt or a document and see the exact token count using gpt-tokenizer, before you find out the hard way that it does not fit the context window.
• LLM Cost Calculator, compare live pricing across every major provider, pulled from the OpenRouter API, so you can estimate a request's cost or pick a cheaper model before it ships in code.
• AI Prompt Builder, structure a prompt with the right sections instead of guessing at formatting from scratch every time.

These three get used constantly when I am estimating the running cost of an agent workflow or deciding which model to route a task to at Sista AI. This is not theoretical for me, it is the same math that goes into real production decisions, and prices change often enough that a static blog post about pricing is out of date within weeks. Pulling live numbers from OpenRouter keeps the comparison honest.

Quick reference: task to tool

If you already know what you need, here is the shortest path to it.

Frequently Asked Questions

Is it safe to paste a real API key or JWT into these tools?

Yes. Every tool runs entirely in your browser using client-side JavaScript. Nothing you paste is uploaded, logged, or sent to a server, there is no backend call to intercept. That is the whole point of building them this way, so you can use real data without exposing it.

Do I need to install anything or sign up?

No. Open the page and use it. There is no account, no email capture, no extension to install, and no rate limit.

Are these tools actually free, or is there a catch later?

Free forever, no catch. There is no premium tier hidden behind these tools and no trial period. I built them for my own use and keep them free for anyone else who needs the same thing.

Why not just use an existing site like a random "json to ts" converter?

You can, but most of those sites are ad-funded, slower to load, and give you no way to verify what happens to your data once you hit convert. These tools skip the ads, skip the server round trip, and keep everything local to your machine.

Can I use these tools for commercial or client work?

Yes, there are no usage restrictions. Use the output in client work, your own product, internal tooling, whatever you need.

Built by a developer, for developers

These 17 developer tools are a small part of a bigger collection I use myself, and I keep adding to it as new needs come up. If one of these saves you a context switch today, it did its job.