🔌 API Integration — External Data

What Is an API?

An API is essentially like a restaurant order form. At a restaurant, you look at the menu, write down your order, and hand it to the kitchen. The chef makes your food and sends it out.

APIs work the same way. You send a “request,” and the server returns “data.” For example, if you request “give me the disclosure list for Samsung Electronics,” the FSS server sends back the disclosure data.

The key point is — you’re using functionality someone else built. If Google built an AI model, you can call that AI via API. If the FSS organized disclosure data, you can fetch that data via API.

Popular Free APIs

Pointing AI to Official Documentation

The most important thing when using APIs is the official documentation. No matter how smart AI is, without official docs it might not know the exact API call format. Parameter names and authentication methods in particular need the docs to be accurate.

There are 4 ways to give AI the official documentation.

Method 1: Save docs as a file

Save the DART API official documentation as dart-api-docs.md.
Then reference that document to write the code.

Claude Code fetches the docs from the official site, saves them as a file, and references that file to write code. Save once and it stays available for future reference.

Method 2: Pass the URL directly

Reference this documentation:
https://opendart.fss.or.kr/guide/main.do

Method 3: Use context7

use context7
Create code that generates images using the Google Gemini API.

Adding “use context7” to your prompt makes Claude Code automatically find and reference the latest library docs. Especially useful for libraries that update frequently.

Method 4: Record in CLAUDE.md

## API Info
- DART API docs: https://opendart.fss.or.kr/guide/main.do
- Gemini API docs: https://ai.google.dev/docs
- Read API keys from .env file

Record API info in CLAUDE.md and Claude Code automatically references it every time, no need to explain again. Definitely record APIs you use frequently in your project.

Content Generation With Gemini API

Google’s Gemini API can handle text, images, and video—it’s a powerful multi-modal AI API. The free tier is sufficient for personal projects, though there are per-minute request limits. Heavy usage requires a paid upgrade.

Getting an API Key

GEMINI_API_KEY=your-api-key-here

Text Generation Example

Using the Gemini API,
create a 60-second Shorts script
on "vibe coding for office workers".
Include per-scene narration + visuals + subtitles.
Read the API key from .env.

Claude Code writes code to call the Gemini API, runs it, and creates the script file for you. You just check the result.

What Gemini Can Do

Automated DART Disclosure Collection

DART is the Electronic Disclosure System operated by Korea’s Financial Supervisory Service. It provides free access to all public filings—annual reports, quarterly reports, material disclosures, and more—for listed companies.

Instead of manually visiting the DART website and clicking through one by one, you can fetch everything at once via API.

Getting an API Key

DART_API_KEY=your-api-key-here

Disclosure Collection + Analysis

Use the DART API to fetch Samsung Electronics'
disclosures from the last 3 months,
select the important ones,
and create an analysis report as report.html.
Read the API key from .env.

Claude Code calls the DART API to fetch the disclosure list, evaluates importance, selects key filings, and creates a polished HTML report. Investment research that used to take 2 hours daily now finishes in 2 minutes.

More possibilities

• Financial statement comparison

  “Create a comparison chart of Samsung and SK Hynix’s revenue/operating profit over the last 3 years”

• Disclosure alert system

  “Check new disclosures for my 10 watchlist stocks every morning and summarize”

• Annual report key extraction

  “Extract just the risk factors and new business initiatives from this company’s annual report”

Shorts Automation Pipeline

Combine the APIs we’ve learned so far and you can build something amazing: a Shorts content auto-production pipeline. From script to video, the entire process can be automated.

Full Pipeline

Create a 60-second Shorts script on
"How to earn $1000/month with vibe coding after work".
Split into 5 scenes with narration, visual description, and subtitles per scene.
Also generate background images for each scene using the Gemini API.

One prompt generates both the script and images simultaneously. What would take a human half a day can be done in under 10 minutes.

Try It Yourself

Pick one challenge below and try it yourself. All use free APIs.

The Gemini API key is in .env.
Generate 5 "motivational messages for office workers".
Each in a different tone (humor, serious, touching, motivational, witty).

The DART API key is in .env.
Fetch Kakao's disclosures from the last month
and organize title, date, and type in a table.

Collect today's "AI" related news,
organize the top 5 stories with title, summary, and source,
and create news-briefing.html.

Verification Checklist

API Best Practices

Essential tips for using APIs safely and efficiently. Follow these and you’ll work cleanly from the start.

GEMINI_API_KEY=your-api-key-here
DART_API_KEY=your-api-key-here
NAVER_CLIENT_ID=your-client-id-here

## API Integration
- DART: https://opendart.fss.or.kr/guide/main.do
- Gemini: https://ai.google.dev/docs
- All API keys read from .env
- DART daily call limit: 10,000