About CodeLint.Dev
CodeLint.Dev is a free collection of more than 120 online tools for developers, finance professionals, and people working with AI. Every tool runs entirely inside your browser — nothing you paste, type, or upload is ever sent to a server. It exists to give you fast, reliable utilities without sign-ups, paywalls, rate limits, or surveillance.
Why we built it
Most online developer tools work by uploading your data to a remote server, processing it there, and sending the result back. That is convenient, but it means your JSON payloads, API responses, JWT tokens, environment files, and other sensitive data leave your machine and pass through infrastructure you do not control. For many of us, pasting an internal API key or a customer record into a random website is simply not acceptable.
CodeLint.Dev takes the opposite approach. Every formatter, validator, converter, generator, and calculator is implemented in JavaScript that runs on your own device. Once a page has loaded, most tools keep working even with your network disconnected. Your data never becomes our data.
What makes it different
100% client-side
Processing happens in your browser. We have no servers that receive your tool input, so there is nothing for us to log, store, or leak.
Instant & offline-capable
No round trip to a server means results appear immediately, and most tools keep working after the page has loaded even without a connection.
Built for real work
Tools include detailed explanations, usage steps, and FAQs — and the blog covers the underlying standards with RFC references and code examples.
Free, with no account
No sign-up, no trial, no premium tier and no rate limits. The interface can also be switched into 19 languages from the header.
What you'll find here
The catalogue is organised into three broad areas:
- • Technical tools — JSON, GeoJSON, and code formatters; JWT, Base64, and URL encoders; regex testing; diffing; hashing; UUID and password generation; date/time utilities; barcode and QR generators; audio utilities; reference data; and network/security helpers.
- • Finance tools — loan and mortgage calculators, compound interest, investment returns, tax estimators, currency conversion, and payment-card validation.
- • AI tools — token counters, cost calculators, prompt builders, model comparisons, and in-depth reference guides for working with large language models.
Who builds it
Mimamsa
Founder & Engineer, CodeLint.Dev
Mimamsa builds and maintains CodeLint.Dev — the whole catalogue, from the JSON and GeoJSON linters through the finance calculators to the AI token and cost tooling. The site grew out of a straightforward frustration: most online utilities upload your data to someone else’s server to do work a browser can do locally, which makes them unusable the moment the input contains an API key, a customer record, or a salary figure. Every tool here is written to run entirely on your own device, and each one ships alongside a written explanation of the standard or formula behind it rather than a bare widget.
Several tools here — the tax estimators, the mortgage and loan calculators, the credit-score model — deal with money, and it is worth being explicit about what they are. They are arithmetic. Each one states the method it uses and, where the result depends on a jurisdiction, which rules it is applying and as of when. None of them is financial advice, none of them knows your circumstances, and none of them should be the last word on a decision that matters. If you find one that is wrong, say so and it will be fixed.
How the project stays free
CodeLint.Dev is supported by unobtrusive advertising and optional reader donations. That revenue covers hosting, domain, and the time spent building and maintaining new tools. Advertising never changes the core promise: your tool input stays in your browser and is never sold or shared. You can read exactly what we collect — and what we don't — in our Privacy Policy.
Get in touch
Questions, bug reports, and tool suggestions are always welcome. Email support@codelint.dev, visit the contact page, or find the project on GitHub. If a tool has saved you time, you can also support its development .