What this is

JSONCraft is a suite of 23 free developer tools that run entirely in your browser — formatters, validators, converters and generators for JSON, YAML, CSV, TOML, XML, regex, base64, hashes, UUIDs, timestamps and cron expressions. No file you load and no value you type is uploaded to a server. Every parse, transform and conversion happens locally on your device, and the result is visible only to you.

Why it exists

Most developer tools online today follow the same pattern: a slow page filled with intrusive ads, a paywall hiding the actually useful features, a forced signup, and an upload step that puts your data on someone else's server. After running into one too many of those, the operator (an independent developer based in Spain) started building self-contained alternatives one tool at a time. JSONCraft is the result for the developer category.

The design philosophy has stayed the same since the first commit: every tool must work without an account, without uploading anything sensitive, and without locking the obvious feature behind a "Pro" button. If a feature genuinely needs server-side computation, it is documented as such and the alternative is offered.

How it is funded

JSONCraft is free, with no signup, no premium tier and no upsell. The site is funded by display ads (Google AdSense) shown around the tools, and by occasional Buy Me a Coffee tips from people who liked the result and wanted to say thanks.

This means the site is sustainable without harvesting your data, gating tools behind a paywall, or pushing you toward a desktop app. If you find one of the tools genuinely useful and want to support continued development, the Buy Me a Coffee link in the footer is the most direct way.

Who is behind it

JSONCraft is built and maintained by Marco B., an independent developer based in Spain. The site is part of a small portfolio of utility web apps (CompoundVision for finance, AllYouNeed for general tools, JSONCraft for developers, OpenImages for image work, OpenPDF for PDFs, PingThat for networking). Each one shares the same private-by-default design.

If you would like to talk to a human about a tool, a bug or a feature you wish existed, the Contact page has a feedback form that lands in the operator's inbox within a few hours during EU working days.

How tools work in your browser

The site is built with Astro, Svelte 5 and Tailwind CSS 4, deployed on Cloudflare Pages. Each tool delegates to a well-tested open-source library or to a native browser API rather than reinventing the parser:

• JSON — formatter, viewer, graph, JSONPath and JSON Schema use the native JSON.parse and JSON.stringify; schema validation uses Ajv.
• YAML / TOML — js-yaml for YAML parsing and serialization; @iarna/toml for TOML.
• CSV — PapaParse, configurable for delimiters, quoted fields and newline conventions.
• XML — native DOMParser + XSLT for formatting.
• Hashes — Web Crypto API SubtleCrypto.digest for SHA-1, SHA-256 and SHA-512; SHA-3 family from an audited polyfill where the browser does not expose it.
• UUIDs — Web Crypto crypto.randomUUID() for v4 (RFC 4122 conformant).
• Regex tester — your browser's native RegExp engine (V8 on Chrome/Edge, SpiderMonkey on Firefox, JavaScriptCore on Safari). Behaviour differences for lookbehind and unicode property escapes follow the engine, not a polyfill.
• Base64 / URL encode — native btoa/atob + TextEncoder/TextDecoder for Unicode-safe round-tripping.
• Cron expression builder — own parser that follows POSIX cron plus the Quartz extensions (?, L, W, #); next-run preview computes in your browser.

No third-party trackers run beyond aggregate Google Analytics 4 (with EU/UK consent gated to "denied" by default). Tool inputs never leave your browser, so there is nothing on a server to ask about under GDPR Article 15 — the full data flow is documented in the Privacy Policy.

Standards we follow

Where a tool implements a published specification, the implementation aims to follow the spec verbatim rather than a forgiving subset. If a discrepancy is found, the bug is in the tool, not in the spec.

• JSON — RFC 8259 and ECMA-404.
• YAML — YAML 1.2 (covering YAML 1.1 compatibility quirks for booleans like yes/no).
• TOML — TOML 1.0.0 (the @iarna/toml library has not yet upgraded to TOML 1.1.0; new 1.1.0 features like extended inline-table syntax may parse incorrectly).
• CSV — RFC 4180 with optional UTF-8 BOM handling.
• UUIDs — RFC 4122 (v4 only — random, not name-based).
• Base64 — RFC 4648 standard + URL-safe variant.
• JSON Schema — draft 2020-12 (older drafts validated via Ajv compatibility modes).
• JSONPath — Goessner's syntax (the de facto reference; the newer RFC 9535, Standards Track since February 2024, has small differences our implementation has not adopted yet).
• Cron — POSIX 1003.2 with Quartz extensions; the builder makes the dialect explicit.

Built for humans and AI engines

Each tool page emits a JSON-LD HowTo schema with the actual step-by-step instructions for using that tool. This is invisible to human readers (it lives in the page's structured-data block) but visible to AI engines like ChatGPT, Perplexity, Bing AI and Claude when they scrape the page for citation extraction. That is why an AI assistant asked "how do I format JSON" or "how do I build a cron expression" can give a short, accurate answer linking back to the specific JSONCraft tool — the steps come from the same source that drives the in-page UI, not from an LLM's best guess.

Google deprecated the HowTo SERP rich-result for non-recipe pages in August 2023, but schema.org structured data remains the canonical semantic layer of a page for crawlers. JSONCraft keeps it because AI-engine citation lift is measurable in bot-traffic logs (GPTBot, PerplexityBot, ClaudeBot, CCBot), independent of whether Google renders a rich snippet.

Editorial independence

The advertising network (Google AdSense) does not influence which tools are built or how they work. There are no sponsored articles, no "best of" lists pushing affiliate links, and no editorial choices made to favour an advertiser. If a tool exists on the site, it is because it was useful enough to the operator to build and ship it.