# How I Built 5 Developer Tool APIs on a Raspberry Pi (And Listed Them on RapidAPI) > Source: > Published: 2026-08-24 07:48:51+00:00 This is a writeup of how I built and launched a small API hub — what worked, what didn't, and the tech stack behind it. The Problem As developers, we use the same tools over and over: prompt optimization, JSON validation, text analysis. These are small, repeatable tasks that don't need a full SaaS — they just need a reliable API endpoint. The Stack Runtime: Python FastAPI in a Docker container Host: Raspberry Pi 4 (8GB) in my garage Tunnel: Cloudflare Tunnel (zero open ports on router) Domain: kowhaigoods.com via GitHub Pages Marketplace: RapidAPI Hub The 5 Endpoints AI Prompt Optimizer POST /prompt-optimizer/optimize Send a raw prompt like "write me a blog post about dogs" and get back a structured prompt with: Role definition ("You are an expert content writer...") Task specification Constraints Output format guidance JSON Schema Validator POST /json-tools/validate Validates JSON data against a schema — useful for CI/CD pipelines and form validation. 3-4. JSON Formatter & Converter Format/beautify JSON with custom indentation, and convert between JSON ↔ CSV ↔ YAML. Text Readability & SEO Analyzer POST /text-analyzer/analyze Returns readability scores (Flesch-Kincaid, Gunning Fog, SMOG), SEO metrics (word count, keyword density, sentence structure), and improvement suggestions. What Worked Free tier is essential. 100 requests/month free. Nobody pays $9.99/mo for an API they haven't tested. SEO + FAQ schema drives organic traffic. Blog posts with FAQPage JSON-LD schema show up in Google's answer snippets. Cloudflare Tunnel is perfect for homelab hosting. No port forwarding, automatic SSL, DDoS protection built in. What Didn't Work (1/2) Reddit r/programming — strict anti-self-promo, post was removed. Use r/SideProject instead. Stack Overflow — any mention of your own product gets flagged. Don't bother. Direct cold outreach to devs — low response rate. Inbound (SEO + marketplace) works better. Try It Free tier: [https://rapidapi.com/kowhai-text-utilities](https://rapidapi.com/kowhai-text-utilities) Full API docs: [https://kowhaigoods.com/api-docs.html](https://kowhaigoods.com/api-docs.html) Blog: [https://kowhaigoods.com/](https://kowhaigoods.com/)