Developer Tools

A web app that bundles 35+ everyday developer tools — JSON and format converters, regex helpers, string and time utilities, encoding/hashing tools, color and network calculators, fake-data and QR generation, Markdown ⇄ PDF conversion, and quick HTTP/MIME reference tables.

The application is split into two pieces:

• backend/ — a FastAPI service exposing every tool as a typed JSON endpoint under /api/....
• frontend/ — a Vite + React + TypeScript single-page app served by the backend in production.

In production both ship in a single Docker image. In development you can run them as two processes (Vite proxies /api to the API).

Tools

JSON

• Validator — validate JSON, optionally against a JSON Schema.
• Schema Generator — produce a draft-04 JSON Schema from a sample.
• Sample Generator — generate sample data conforming to a schema (handles enum, pattern, format, allOf/anyOf/oneOf, if/then/else).
• String ⇄ JSON Converter — turn JSON into an escaped string and back.
• Parser — pretty-print JSON.
• JSONPath — evaluate a JSONPath expression against a JSON document.

Convert

• Format Converter — convert between JSON, YAML, TOML, XML, and CSV (CSV round-trips a list-of-objects shape).
• cURL Converter — turn a curl command into fetch, axios, and Python requests code.

RegEx

• Checker — test a pattern against a string. Each call is bounded to 1 s of CPU and rate-limited (15/min by default) to mitigate ReDoS.
• Generator — suggest a regex for an input; recognises emails, phone numbers, ISO dates, and SSNs.

String

• Diff Viewer — side-by-side diff with line numbers and per-row colouring.
• Char/Word Counter — character/word/line count, with optional custom delimiter.
• Column Extractor — pull a column out of delimited text.
• Clean Text — strip leading/trailing whitespace plus hidden/zero-width and control characters; preserves case and internal whitespace, with an optional toggle to collapse runs of spaces (keeping newlines).
• Text Statistics — char/word/sentence counts plus min/max/avg word length.
• Random Number / Random String / Shuffle Letters.

Encoding

• Base64 — encode/decode UTF-8 text.
• URL Codec — URL-encode/decode text and parse a query string into key/value pairs.
• Hash & HMAC — MD5/SHA-family digests and keyed HMAC digests.
• JWT Viewer — decode HS256 tokens.
• JWT Signer — sign a payload with HS256/384/512.
• UUID — generate (v1/v3/v4/v5/v7) and inspect/validate UUIDs.
• Case Converter — convert between camelCase, snake_case, kebab-case, CONSTANT_CASE, Title Case, and more.

Time

• Time Converter — accepts ISO-8601, epoch seconds, epoch milliseconds, and YYYY-MM-DD HH:MM:SS Postgres timestamps; emits Eastern, UTC, UNIX, day-of-week/year, leap-year, and several locale formats.
• CRON Scheduler — build a CRON expression from form fields.
• CRON Next Runs — list the next N times a CRON expression will fire, in a chosen timezone.

Calc

• Color — convert a color between hex, RGB, HSL, and OKLCH, and check WCAG contrast ratios.
• chmod Calculator — convert Unix permissions between numeric and symbolic forms.
• CIDR Calculator — derive network/broadcast addresses, host range, and host count for an IPv4/IPv6 subnet.

Document

• Markdown ⇄ PDF — render Markdown to a downloadable PDF (headings, bullets, fenced code) or extract text from a PDF.
• Markdown Preview — render Markdown to HTML (fenced code, tables, lists).

Fake Data

• Generator — build a synthetic dataset of up to 1000 records with 25+ field types (names, emails, vehicle make/model pairs, license plates, etc.) and export as JSON or CSV.
• Lorem Ipsum — generate filler words, sentences, or paragraphs.
• QR Code — encode text or a URL as an SVG QR code.

Reference

• HTTP Statuses — searchable reference of HTTP status codes.
• MIME Types — common Content-Type / file-extension reference.

Architecture

┌────────────────────────────────────────────────┐
│              single Docker image               │
│                                                │
│  uvicorn (FastAPI)                             │
│     ├─ /api/*  → routers/ → services/          │
│     │      json, convert, regex, string,       │
│     │      encoding, codec, time, calc,        │
│     │      document, fake_data, misc           │
│     └─ /*      → SPA (Vite build)              │
└────────────────────────────────────────────────┘
                        │
                        └── redis  (slowapi rate limiting)

• Pure-function services in backend/app/services/ hold the heavy lifting; routers stay thin. This is what makes the helpers easy to unit-test.
• Pydantic v2 request/response models on every endpoint give automatic validation and a useful /docs (Swagger) page.
• slowapi sits in front of expensive routes (/api/regex/check, /api/json/sample). It uses Redis when REDIS_URL is set and falls back to in-memory storage otherwise.

Local development

Prerequisites: Python 3.10+, Node 20+, uv.

Backend

cd backend
uv sync                              # install deps into .venv
uv run uvicorn app.main:app --reload # http://localhost:8000
uv run pytest                        # run the test suite

OpenAPI docs: http://localhost:8000/docs.

Frontend

cd frontend
npm install
npm run dev                          # http://localhost:5173

The dev server proxies /api → http://localhost:8000, so just run both processes side by side.

Docker (single command, recommended)

docker compose up --build
# everything on http://localhost:8000

One container: a multi-stage build assembles the SPA with node:20-alpine, then python:3.12-slim installs runtime deps with uv sync --no-dev and serves both the API and the built SPA from a single uvicorn process. SPA_DIST points at the built assets.

Docker (dev with hot reload)

docker compose -f docker-compose-dev.yml up --build
# API:    http://localhost:8000
# Vite:   http://localhost:5173

Docker (prod with nginx + redis + TLS)

For deployments that want TLS termination and Redis-backed rate limiting:

docker compose -f docker-compose-prod.yml up --build

You'll need self-signed certs in certs/ (see below) before bringing up the nginx container.

For HTTPS, generate (or replace) certs/nginx-selfsigned.{crt,key}:

mkdir -p certs && cd certs
openssl req -x509 -nodes -days 365 -newkey rsa:2048 \
  -keyout nginx-selfsigned.key -out nginx-selfsigned.crt

Configuration

All settings are read from environment variables (or a backend/.env file).

Variable	Default	Description
LOG_DIRECTORY	logs/	Log file directory; created on startup.
REDIS_URL	(unset → in-memory)	Storage URI for the slowapi limiter.
SPA_DIST	<repo>/frontend/dist	Path to the built SPA.
CORS_ORIGINS	http://localhost:5173,http://127.0.0.1:5173	Allowed dev origins.
RATE_LIMIT_DEFAULT	60/minute	Default per-IP limit.
RATE_LIMIT_REGEX_CHECK	15/minute	Limit on /api/regex/check.
RATE_LIMIT_JSON_SAMPLE	30/minute	Limit on /api/json/sample.

API quick reference

Every endpoint returns JSON unless noted. All POST bodies are JSON.

Method	Path	Notes
POST	/api/json/validate
POST	/api/json/schema
POST	/api/json/sample	rate-limited
POST	/api/json/convert
POST	/api/json/parse
POST	/api/convert/format	JSON/YAML/TOML/XML/CSV
POST	/api/convert/jsonpath	evaluate a JSONPath expression
POST	/api/convert/curl	curl → fetch / axios / requests
POST	/api/regex/check	rate-limited; 1 s timeout
POST	/api/regex/generate
POST	/api/string/diff	structured hunks
POST	/api/string/count
POST	/api/string/columns
POST	/api/string/clean
POST	/api/string/stats
POST	/api/string/random-number
POST	/api/string/random-string
POST	/api/string/shuffle
POST	/api/encoding/base64
POST	/api/encoding/jwt	decode
POST	/api/codec/url	URL encode/decode
POST	/api/codec/url/parse	parse query string
POST	/api/codec/hash	MD5/SHA digests
POST	/api/codec/hmac	keyed HMAC digest
POST	/api/codec/case	case conversion
POST	/api/codec/uuid/generate	UUID v1/v3/v4/v5/v7
POST	/api/codec/uuid/inspect	parse/validate a UUID
POST	/api/codec/jwt/sign	sign HS256/384/512
POST	/api/time/convert
POST	/api/time/cron
POST	/api/calc/cron-next	next N cron run times
POST	/api/calc/color	hex/RGB/HSL/OKLCH
POST	/api/calc/contrast	WCAG contrast ratio
POST	/api/calc/chmod	numeric ⇄ symbolic
POST	/api/calc/cidr	subnet calculator
POST	/api/calc/markdown	Markdown → HTML
POST	/api/document/md-to-pdf	streams application/pdf
POST	/api/document/pdf-to-md	multipart upload
GET	/api/fake-data/types	list of supported field types
POST	/api/fake-data/preview
POST	/api/fake-data/export	streams CSV or JSON
GET	/api/misc/http-statuses	HTTP status reference
GET	/api/misc/mime-types	MIME-type reference
POST	/api/misc/lorem	lorem ipsum generator
POST	/api/misc/qr	SVG QR code
GET	/api/health

Contributing

1. Fork the repo and create a branch.
2. Make changes; add or update tests in backend/tests/.
3. Ensure cd backend && uv run pytest and cd frontend && npm run build both pass.
4. Open a PR.

License

MIT — see LICENSE.