Every developer has the same ritual. You need to format some JSON, so you Google "json formatter online." You click the first result. You're greeted by:
- A banner ad covering half the screen
- A cookie consent popup
- A newsletter modal
- A layout that hasn't been updated since jQuery was cool
You paste your JSON, click format, and it works. But you feel dirty.
I got tired of this. So I built JSON Knife — 19 developer tools that are fast, clean, and free. No ads, no signup, no popups. Just tools.
What's in the box
Here's the full list:
| Tool | What it does |
|---|---|
| JSON Formatter | Beautify, minify, syntax highlighting |
| JSON Validator | Find exactly where your JSON is broken |
| JSON Diff | Compare two JSON objects side by side |
| JSON ↔ YAML | Convert between JSON and YAML |
| JSON ↔ CSV | Convert flat JSON arrays to CSV and back |
| JSON ↔ TOML | Convert between JSON and TOML |
| Regex Tester | Live matching with group extraction |
| SQL Formatter | Format and minify SQL with dialect support |
| JWT Decoder | Inspect JWT header and payload |
| Cron Generator | Visual builder with human-readable explanations |
| Docker Compose | Build docker-compose.yml visually with templates |
| Mermaid Editor | Create diagrams with live preview |
| Git Commands | Searchable reference with workflow templates |
| Base64 | Encode and decode |
| URL Encode | Encode and decode URL strings |
| UUID & Hash | Generate UUIDs and compute SHA hashes |
| Epoch Converter | Unix timestamps ↔ human dates |
| Color Converter | HEX, RGB, HSL, HSB with contrast checker |
| HTML Entities | Encode and decode HTML entities |
Try it: tools.shanecode.org
Why I built it this way
Everything runs in your browser
Zero server calls. Your data never leaves your machine. I paste production configs, API keys, and real JWTs into these tools daily — I needed to trust them completely.
The entire site is a static SvelteKit app hosted on Cloudflare Pages. There's no backend. No database. No analytics tracking your keystrokes.
Svelte 5 was the right call
I built this with Svelte 5 and its new runes reactivity system. Every tool updates instantly as you type — no debouncing, no "click to format" buttons where they aren't needed. The JSON formatter highlights syntax in real-time. The regex tester shows matches as you edit the pattern.
Svelte 5 compiles away the framework overhead, so the tools feel native. The entire site loads in under a second on a cold cache.
The tools I actually use
Out of 19, three get daily use from me:
Cron Generator — I can never remember cron syntax. Is the day-of-week field 0-indexed or 1-indexed? Does */5 mean every 5 or every 5th? The visual builder eliminates the guesswork. You click the schedule you want and it generates the expression with a plain-English explanation.
Docker Compose Builder — Writing YAML by hand is asking for indentation bugs. The builder has templates for common services (Postgres, Redis, Nginx, Node) and generates valid YAML with proper structure. I use it every time I scaffold a new project.
JSON Diff — When an API response changes and you can't figure out what's different, paste the old and new responses and see exactly which keys changed, were added, or were removed.
What I learned building this
1. Developer tools are SEO gold
Every tool page targets a specific search query. "JSON formatter online" gets hundreds of thousands of searches per month. "Cron expression generator" gets tens of thousands. By building 19 tools, I'm casting 19 nets.
Each tool page has its own meta tags, its own SEO content block explaining what the tool does and when to use it, and its own entry in the sitemap. It's a lot of upfront work, but it compounds.
2. "No ads" is a feature
The bar for developer tools is underground. If your tool loads fast and doesn't assault users with popups, you've already differentiated. I put "No ads, no popups. Free." in the meta description and it's the most effective copy I've written.
3. Ship the boring version first
The first version of JSON Knife had exactly one tool: a JSON formatter. I shipped it, used it myself for a week, then added the validator. Then the YAML converter. Then I couldn't stop.
Each tool took 1-3 hours to build. The Mermaid editor was the most complex (live diagram rendering). The Base64 encoder was the simplest (20 minutes). Starting small let me build momentum.
4. Cross-linking your own products works
JSON Knife is free, but it's also a funnel. At the bottom of the page, there are cards linking to my other products:
- SvelteUI Pro — a premium Svelte 5 component library
- SvelteShip — a SaaS starter template for SvelteKit
- MetaScrape — a URL metadata extraction API
The free tool brings developers in. The paid products are there when they need them. No hard sell, just a small section at the bottom.
Tech stack
For the curious:
- Framework: SvelteKit with adapter-static (fully pre-rendered)
- Styling: Tailwind CSS 4
- Hosting: Cloudflare Pages (free tier)
- Backend: None. Everything is client-side JavaScript.
- Build time: ~2 seconds
- Bundle size: Each tool page loads only what it needs
Total hosting cost: $0/month.
What's next
I'm planning to add more tools based on what developers actually use. A few on the shortlist:
- Markdown preview
- JSON Schema validator
- CIDR/subnet calculator
- .env file editor
If there's a tool you reach for daily that's stuck behind ads and popups, I'd love to hear about it.
Try it out: tools.shanecode.org
I'm Shane, a solo developer building tools at shanecode.org. If you're working with Svelte 5, check out SvelteUI Pro (component library) and SvelteShip (SaaS starter). If you need URL metadata extraction, MetaScrape has a free tier.
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