How to Build a Website SEO Audit Tool in JavaScript (Free APIs)

Ever wanted to quickly check a website's SEO health without paying for expensive tools like Ahrefs or Semrush? You can build your own basic SEO auditor in under 100 lines of JavaScript using free APIs. In this tutorial, we'll build a CLI tool that: Scrapes any page for meta tags, headings, and links Checks DNS records and hosting info Takes a visual screenshot Generates a clean audit report What You'll Need Node.js 18+ A free API key from Agent Gateway (200 free credits, no card required) Step 1: Get Your API Key curl -X POST https://api.frostbyte.world/api/keys/create Save the key from the response. Each API call costs 1 credit, so one full audit uses ~4 credits. Step 2: The SEO Audit Script Create seo-audit.js : const API_KEY = process . env . FROSTBYTE_KEY || ' your-key-here ' ; const BASE = ' https://api.frostbyte.world ' ; async function api ( path ) { const res = await fetch ( ` ${ BASE }${ path } ` , { headers : { ' x-api-key ' : API_KEY } }); return res . json (); } async funct