forge

An in-browser code playground built on the Monaco editor with a Rust + axum backend on Fly.io. Type code and a pure-logic tokenizer analyzes it server-side, streaming back live token counts, complexity metrics, and diagnostics — balance checks, unterminated literals, marker comments. The backend also re-indents brace-delimited code on request.

Highlights

• Rust language toolkit — a dependency-free, C-family tokenizer (the real engine) feeds an analysis pass that reports tokens, aggregate metrics, and diagnostics. Pure logic, fully unit-testable, no I/O in the core.
• Analyze-on-type — the editor debounces keystrokes and POSTs the buffer to the backend, which returns tokens, diagnostics, and metrics for a live readout.
• Real diagnostics — delimiter balance (with mismatch and unclosed detection), unterminated strings and block comments, and TODO/FIXME markers, each with line/column positions.
• Server-side formatter — a conservative indentation normalizer that re-indents by net delimiter depth (ignoring brackets inside strings and comments) and leaves multi-line string interiors untouched.
• Monaco editor — the engine behind VS Code, integrated via a dynamic, client-only import with light/dark themes wired to the site theme.
• Honest states — request timeouts and backend errors surface clearly rather than failing silently.

Tech stack

Frontend: Next.js 14 (App Router) · TypeScript · Tailwind CSS · Framer Motion · @monaco-editor/react Backend: Rust · axum · tower-http (CORS) · serde (deployed on Fly.io)

Project structure

Path	Purpose
server/src/lexer.rs	Pure C-family tokenizer with positions
server/src/analyze.rs	Metrics, balance checking, and diagnostics
server/src/format.rs	Conservative indentation normalizer
server/src/handlers.rs	HTTP handlers over the pure core
web/components/playground/	Monaco editor, toolbar, diagnostics, metrics bar
web/lib/api/	Typed fetch client and the shared wire types
web/lib/hooks/	Debounced analyzer, theme, scroll spy, reduced motion

Local development

# terminal 1 — the language toolkit service
cd server
cargo run
# serves http://localhost:8080 (POST /analyze, POST /format)

# terminal 2 — the playground
cd web
npm install
NEXT_PUBLIC_API_URL=http://localhost:8080 npm run dev

Open http://localhost:3000.

Scripts

Command	Action
npm run dev	Start the dev server
npm run build	Production build
npm run lint	ESLint (next/core-web-vitals)
npm run typecheck	TypeScript, no emit
cargo run	Run the toolkit service
cargo build --release	Release build of the server

Deployment

• Backend → Fly.io from server/ via its Dockerfile, on an always-on machine.
• Frontend → Vercel with the project Root Directory set to web, and NEXT_PUBLIC_API_URL set to https://<your-app>.fly.dev (no trailing slash).

License

MIT — see LICENSE.