The AI producer

Posted on Jun 28

20 Free APIs That Let You Build a SaaS in a Weekend (Cheat Sheet Inside)

#api #tutorial #productivity #opensource

I just finished documenting 20 production-ready APIs with copy-paste code snippets. No signups, no complex auth — just grab the endpoint and start building.

Here are 5 of the most powerful ones.

1. OpenAlex — 250M+ Academic Papers, Free

Want to add E-E-A-T authority to your content? OpenAlex gives you access to 250 million academic works.

import requests

url = "https://api.openalex.org/works"
params = {
    "search": "large language models",
    "filter": "from_publication_date:2025-01-01,open_access.oa_status:gold",
    "sort": "cited_by_count:desc",
    "per_page": 10,
    "mailto": "your@email.com"  # 5x higher rate limits!
}
response = requests.get(url, params=params)
for work in response.json()["results"][:5]:
    print(f"{work['title']} ({work['cited_by_count']} citations)")

Add ?mailto=your@email.com to any request and your rate limits go from 10/sec to 50/sec. No signup required.

2. CoinGecko — Real-Time Crypto Prices

Track 10,000+ cryptocurrencies. Zero authentication needed on the free tier.

url = "https://api.coingecko.com/api/v3/simple/price"
params = {
    "ids": "bitcoin,ethereum,solana",
    "vs_currencies": "usd",
    "include_market_cap": "true",
    "include_24hr_change": "true"
}
response = requests.get(url, params=params)
print(response.json())

Combine this with a QR code API and you've got a crypto portfolio tracker in 50 lines of code.

3. Open-Meteo — Weather Forecasts + Air Quality

No API key. No account. 10,000 requests per day. Free.

url = "https://api.open-meteo.com/v1/forecast"
params = {
    "latitude": 1.35, "longitude": 103.82,
    "daily": "temperature_2m_max,temperature_2m_min,precipitation_sum",
    "timezone": "Asia/Singapore",
    "forecast_days": 7
}
response = requests.get(url, params=params)
for i, date in enumerate(response.json()["daily"]["time"]):
    print(f"{date}: {response.json()['daily']['temperature_2m_max'][i]}C")

There's also a separate air quality endpoint. Two APIs for the price of zero.

4. OpenRouter — 100+ LLMs Through One API

This is the game-changer. Access GPT-4, Claude, Llama, Mistral, and 100+ other models through a single unified API. Some models are completely free.

headers = {"Authorization": "Bearer YOUR_KEY"}
payload = {
    "model": "meta-llama/llama-3.1-8b-instruct:free",
    "messages": [{"role": "user", "content": "Explain REST APIs in one sentence."}]
}
response = requests.post("https://openrouter.ai/api/v1/chat/completions",
                          headers=headers, json=payload)
print(response.json()["choices"][0]["message"]["content"])

Free models are perfect for prototyping. Pay-per-token for production.

5. Imgflip — Meme Generation API

Yes, there's an API for memes. 1,500+ templates, no auth required.

import requests
url = "https://api.imgflip.com/caption_image"
data = {
    "template_id": "181913649",
    "text0": "Writing docs from scratch",
    "text1": "Using a cheat sheet"
}
response = requests.post(url, data=data)
print(f"Meme: {response.json()['data']['url']}")

Build a social media bot that auto-generates memes about your niche. Viral content, zero effort.

The Full Collection

These 5 APIs are just the start. I documented 20 APIs across 4 categories:

Category	APIs
Data and Finance	CoinGecko, ExchangeRate-API, Alpha Vantage, OpenAlex, CrossRef
Content and Media	Imgflip, Open-Meteo, Sunrise Sunset, QR Server, Dictionary
Developer Tools	GitHub, Cloudflare, Vercel, Supabase, Railway
AI and ML	HuggingFace, Stability AI, OpenRouter, Whisper, ElevenLabs

Every API includes:

Base URL and authentication method
Rate limits
Key endpoints with copy-paste code
Pro tips and gotchas

Get the full cheat sheet — 24 pages, $9.99

3 Micro-SaaS Ideas Using These APIs

1. Crypto Dashboard (CoinGecko + Open-Meteo + QR Server)
Real-time prices + weather data + QR codes for sharing. Charge $5-15/month.

2. Research Summarizer (OpenAlex + CrossRef + Whisper)
Search papers, get citations, generate audio summaries. Sell for $9.99 one-time.

3. Content Repurposer (OpenRouter + ElevenLabs)
Convert blog posts to tweets, audio, and video scripts. $7-20/month SaaS.

Each of these can be built in a weekend. The APIs do the heavy lifting.

What's your go-to free API? Drop it in the comments — I might add it to Volume 3.

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