How I Built 10 FastAPI Micro-APIs for AI Agents, RAG & B2B SaaS ($0 Infra & Free Tiers)

keenfolk1-lgtm — Thu, 29 Oct 2026 19:04:42 +0000

Building modern AI agents, RAG pipelines, and B2B SaaS products often means paying $49–$199/mo for bloated enterprise subscriptions just to solve one specific microservice problem — like stripping HTML noise before embedding, blocking prompt injections, catching disposable/alias trial abuse, or generating vector PDF invoices without a heavy headless Chrome container.

Over the past few weeks, I built and deployed a suite of 10 focused FastAPI micro-APIs on RapidAPI Hub — engineered for low latency, clean JSON schemas, and generous free tiers (150–250 requests/month at $0.00/mo).

Here is a look at the architecture, code examples, and how I solved Render's 750-hour free-tier workspace ceiling across 10 concurrent services.

1. AI, RAG & Security Stack (`CleanRead AI`, `PromptShield AI`, `RankPulse SEO`)

CleanRead AI — Web-to-Markdown & Breadcrumb RAG Chunker

Raw HTML wastes 80–90% of an LLM's context window on navbars, inline SVGs, and scripts. Worse, naive character chunking loses section hierarchy.

Live Hub: CleanRead AI on RapidAPI
What it does: Extracts clean GitHub-Flavored Markdown and splits documents into heading-contextualized chunks ("Guide > Installation > Docker") with token estimates.

PromptShield AI — `<5ms` Prompt Injection, PII & Secret Firewall

Live Hub: PromptShield AI on RapidAPI
What it does: Deterministically catches instruction overrides (including Base64-encoded and Zero-Width Unicode obfuscated jailbreaks), redacts Luhn-verified credit cards, IBANs, SSNs, emails, and 13 cloud/AI secret formats (sk-proj-..., AWS, GitHub PAT, Stripe) in under 5ms.

import requests

resp = requests.post(
    "https://promptshield-ai-prompt-injection-pii-secret-guard-api.p.rapidapi.com/api/v1/scan",
    headers={
        "X-RapidAPI-Key": "YOUR_RAPIDAPI_KEY",
        "X-RapidAPI-Host": "promptshield-ai-prompt-injection-pii-secret-guard-api.p.rapidapi.com",
    },
    json={"text": "Contact user@example.com with key sk-proj-1234567890abcdefghij", "redact_mode": "placeholder"},
).json()
print(resp["sanitized_text"])
# -> "Contact [EMAIL_1] with key [OPENAI_API_KEY_1]"

RankPulse SEO — On-Page Audit, SERP Pixel Simulator & AI Search (GEO)

Live Hub: RankPulse SEO on RapidAPI
What it does: Audits proportional Arial pixel widths (600px desktop / 540px mobile), JSON-LD @graph schemas, /llms.txt, and RFC 9309 robots.txt access across 8 AI crawlers (GPTBot, ClaudeBot, PerplexityBot, OAI-SearchBot, Google-Extended, CCBot).

2. B2B Lead Enrichment & Anti-Fraud Stack (`MailShield`, `StackRadar B2B`, `DialGuard`)

MailShield — Disposable Email & Anti-Fraud Verification API: Detects 100k+ temp-mail domains, fingerprints disposable MX servers (1secmail, h-email.net), unmasks Gmail +alias & dot tricks (j.doe+trial99@googlemail.com -> jdoe@gmail.com), and checks live MX/SPF/DMARC.
StackRadar B2B — Tech Stack, DNS & Contact Lead API: Extracts 115+ technology signatures, B2B buying/hiring signals (is_actively_hiring, has_payment_checkout), corporate email provider (Google Workspace vs M365), and public contact emails/socials from any domain.
DialGuard — Global Phone, Carrier, Timezone & TCPA API: Validates phones across 240+ countries (libphonenumber + IANA tzdata), formats to E.164 & WhatsApp (wa.me), detects mobile vs VoIP, and verifies FCC TCPA quiet hours (8am–9pm recipient local time) before AI voice agents (Vapi, Bland, Twilio) dial.

3. FinTech, PDF Invoicing & Media Stack (`FinGuard`, `InvoiceForge`, `QrForge Studio`, `StreamSnap`)

FinGuard — IBAN, EU VAT, Card Luhn & Global Tax Check API: 79-country ISO 13616 IBAN decomposition, live European Commission VIES VAT company lookup, French SIREN / Australian ABN checksums, and EU B2B Reverse-Charge tax calculation.
InvoiceForge — Instant PDF & HTML Invoice & Receipt API: Pure-Python Vector PDF 1.4 (%PDF-1.4) & HTML5 invoices, quotes, credit notes, and PAID webhook receipts in <5ms with Decimal-exact multi-rate VAT accounting across 28 ISO 4217 currencies.
QrForge Studio — Custom QR, WiFi, vCard & Payment SVG API: Vector SVG & high-DPI PNG QR codes with square | rounded | dots modules, center badges, and European EPC SEPA Instant Bank Transfer QR codes.
StreamSnap — Social Video No-Watermark & Audio Extractor API: Direct CDN no-watermark MP4 video & MP3 audio stream extractor for Whisper AI transcription & creator bots.

Solving the Render Free-Tier 750-Hour Math Across 10 Services

Render gives 750 Free Instance Hours / month shared across the entire workspace. If you naively ping 10 services every 10 minutes (24/7), you consume 10 × 24h × 31d = 7,440h/mo and suspend your entire account in 3.1 days.

Instead, I built a quota-safe GitHub Actions monitor (3x/day every 8 hours + RapidAPI's 1x/day daily health check). Since each wake window lasts 15 minutes (0.25h), all 10 services consume just 310h / 750h (41.3%) per month — leaving 440h/mo (~1,760 active 15-minute traffic windows) for real API users while automatically opening a GitHub Issue alert if any endpoint ever degrades.

Try the APIs (Free Tiers Live)

All 10 APIs are live on RapidAPI Hub with interactive Swagger playgrounds and permanent $0.00/mo Basic plans:
👉 Explore the full 10-API Portfolio on RapidAPI Hub (keenfolk1lgtm)

Feedback, feature requests, or questions about the FastAPI / Render architecture are super welcome in the comments!

DEV Community: keenfolk1-lgtm

How I Built 10 FastAPI Micro-APIs for AI Agents, RAG & B2B SaaS ($0 Infra & Free Tiers)

1. AI, RAG & Security Stack (CleanRead AI, PromptShield AI, RankPulse SEO)