Developer Guides
Copy-paste tutorials for common API problems — CORS fixes, validation, PDFs, geolocation, and more.
Fix CORS Errors in JavaScript: the 5-Minute Proxy Solution
Browsers block cross-origin fetches that lack an Access-Control-Allow-Origin header. Fix it in five minutes by routing the request through a CORS proxy.
2026-06-09
Validate Email Addresses in One API Call (Free Tier)
Validate email syntax, MX records, disposable domains, role accounts, and typo suggestions with a single GET request. Free tier: 1,000 checks per month.
2026-06-09
Merge PDFs Programmatically with a Simple REST API
Combine PDF files with one REST call. Send URLs or base64 inputs, get the merged document back as base64. No native libraries, free tier included.
2026-06-09
Free Currency Exchange Rate API with Live ECB Rates
Convert currencies with European Central Bank reference rates, refreshed each business day. 30+ currencies, free tier of 1,000 requests per month.
2026-06-09
Free IP Geolocation API: Country, City, Timezone in One Call
Resolve any IPv4 or IPv6 address to country, city, coordinates, and timezone with one GET request. GeoLite2-backed with no per-call data fees.
2026-06-09
Convert Coordinates to Plus Codes (Open Location Code) via API
Encode latitude and longitude into Plus Codes (Open Location Code) and decode them back via REST. Geohash, distance, and coordinate conversion included.
2026-06-09
Redact PII from Text Before It Hits Your Logs or an LLM
Detect and redact emails, phone numbers, SSNs, credit cards, and IPs in one request. Returns masked text plus counts by type; detect-only mode included.
2026-06-09
Generate QR Codes via API: PNG, SVG, or Data URI
Generate QR codes server-side with one GET request. PNG bytes, scalable SVG, or an embeddable data URI, with size, margin, and color options.
2026-06-09
Loan & Mortgage Calculator API: Monthly Payments and Amortization
Calculate monthly loan payments, total interest, and a full amortization schedule with one GET request. Plus compound interest, ROI, VAT, and tip math.
2026-06-24
Generate Mock Test Data via API (Seeded & Reproducible)
Generate realistic fake users, addresses, and companies as JSON with one request. Pass a seed for reproducible fixtures in tests, demos, and dev databases.
2026-06-24
Parse User-Agent Strings via API: Browser, OS & Device
Turn any User-Agent string into structured browser, engine, OS, and device fields with one GET request. No local UA database to ship or keep updated.
2026-06-24
Phone Number Validation API: Validate & Format to E.164
Validate phone numbers, detect country and line type, and format to E.164 and national formats with one GET request. Built on Google's libphonenumber.
2026-06-24
Resize, Convert & Compress Images via API
Resize, crop, convert (WebP/PNG/JPEG), and compress images with a single API call. No native image library to install and no servers to run.
2026-06-24
zxcvbn as an API: Password Strength Scoring + HIBP Breach Checks
Run Dropbox's zxcvbn password strength estimator as an API call — realistic crack times and feedback — plus Have I Been Pwned breach checks via k-anonymity. Nothing stored.
2026-07-01
DNS Lookup API: A, MX, TXT, and More Records in JSON
Query A, AAAA, MX, TXT, NS, CNAME, and SOA records for any domain over HTTPS with one GET request. JSON in, JSON out — no dig or resolver required.
2026-06-24
Sunrise & Sunset API: Golden Hour, Solar Position, Moon Phase
Get sunrise, sunset, golden hour, dawn/dusk, solar position, and moon phase for any coordinates and date with one GET request. Pure astronomical math, nothing stored.
2026-07-02
Unit Conversion API: Length, Mass, Temperature, and 7 More Categories
Convert between metric and imperial units — length, mass, temperature, volume, area, speed, data size, time, pressure, energy — with one GET request. Category auto-detected.
2026-07-02
WCAG Contrast Checker API: Ratios, AA/AAA, and Color Conversion
Check WCAG 2.x contrast ratios with AA/AAA pass-fail, convert colors between hex/RGB/HSL/HSV/CMYK, and generate palettes — one pure-math API call.
2026-07-02
NAICS Code API: Semantic Lookup from Any Business Description
Classify companies into 2022 NAICS codes from plain-English descriptions with a 0–100 match rating. Semantic matching finds the right code even when your words differ from the official titles — from $0 for 1,000 calls/month.
2026-07-06