Most free dev tools online only handle one file at a time. Resize one image, convert one CSV, decode one JWT — and if you have 40 files instead of 1, you're either doing it manually or paying for a "pro" tier just to unlock batch support.
So I built FreeToolDev: a collection of free, browser-based batch utilities, built from the ground up to handle multiple files or entries at once.
What's in it (9 tools so far)
- Bulk Image Resize/Convert/Compress — resize, convert, or compress dozens of images at once
- CSV to JSON (Batch) — with automatic UTF-8/EUC-KR/UTF-16 encoding detection
- Base64 Encode/Decode — batch, line by line
- Bulk QR Code Generator — up to 100 codes at once
- JWT Decoder (Batch) — fully client-side, no signature verification claimed
- RSS Generator, Sitemap Generator
- IP/DNS/SSL Bulk Lookup
- Site Crawler & Audit — crawls up to 40 pages, checks broken links and meta tags
How it's built
Everything runs client-side — nothing gets uploaded to a server. No account, no signup, completely free. The heavier tools (site crawling, SSL lookups) use a small Cloudflare Worker as a backend, since a few things (like SSL cert lookups via crt.sh) can't be done purely in the browser due to CORS.
What I learned
Building for batches instead of single files changes a lot of small decisions — chunked parsing so large CSVs don't freeze the tab, sequential processing with progress indicators for image conversion, queuing with concurrency limits for SSL lookups so you don't hit rate limits. None of it is complicated individually, but it's the kind of detail that's easy to skip when you're just building a single-file tool.
If you build one-off scripts to batch-process files, I'd love to hear what other "one at a time" tools annoy you the most — might be the next thing I add.
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