Kroki vs Wandbox

Kroki puts a single unified HTTP API in front of two dozen open-source diagram-as-code renderers, including PlantUML, Mermaid, GraphViz, D2, BPMN, Excalidraw, and WaveDrom, so callers send diagram source text and get back an image with no local toolchain to install. A GET request embeds the (deflate+base64-encoded) diagram directly in the URL, making it trivial to drop live diagrams straight into Markdown or HTML. The project and its public instance at kroki.io are free and open source, with self-hosting via Docker documented for anyone who needs a private instance.

Wandbox is a free "social compilation service" built by melpon and kikairoya, offering 175 compiler configurations across 35 languages — from mainstream C++, Python, Rust, and Go to niche picks like Lazy K and Pony — including nightly HEAD builds of GCC and Clang. Its REST API needs no key: POST source code, a compiler ID, and options to /api/compile.json (or the /ndjson variant for streamed output) and get back compile/runtime output plus a permanent shareable permalink, while /api/list.json enumerates every compiler and its supported switches. The project was rewritten in 2024–2026 from a legacy Ruby backend to Rust (feline) and Remix (canine), which is why the old kennel2/API.rst docs path 404s — the live API endpoints themselves are unchanged.