Week 2: Installing & First Run¶

What you'll learn: - LLM providers (Anthropic, OpenAI, Ollama) - API keys vs. subscriptions - The OpenCode TUI and keyboard shortcuts - The /init command and AGENTS.md - Your first real task: fix a typo

What is an LLM Provider?¶

A company (or service) that runs a language model and gives you access to it.

OpenCode is provider-agnostic — works with multiple providers.

Three main options: 1. Anthropic (Claude) 2. OpenAI (GPT) 3. Local Ollama (offline, free)

Option 1: Anthropic (Claude)¶

What: Claude family of LLMs (Opus, Sonnet, Haiku)

Access: API key or Claude.ai subscription

Cost: Pay-as-you-go (~$0.003 per 1K input tokens with Sonnet)

Best for: Learning. Excels at coding. Default for this course.

Sign up: console.anthropic.com

Option 2: OpenAI (GPT)¶

What: GPT-4, GPT-4o, GPT-3.5-turbo

Access: API key or ChatGPT Plus subscription

Cost: Pay-as-you-go (~$0.005 per 1K input tokens for GPT-4o)

Best for: If you already have an OpenAI account.

Trade-off: More expensive, but widely adopted.

Sign up: platform.openai.com

Option 3: Local Ollama¶

What: LLM server runs on your machine

Access: Free, no API key needed

Cost: Zero (after download)

Best for: Offline work, privacy, no budget

Trade-off: Models less capable than cloud APIs. Okay for Weeks 1–3.

Download: ollama.ai

API Keys vs. Subscriptions¶

Aspect	API Key	Subscription
How	Secret token + pay per request	Monthly flat fee
For	OpenCode + integrations	Web chat only (Claude.ai, ChatGPT)
Cost	$5–30/month if careful	$20/month flat
For this course	Use API key	Don't use subscription

Why API key? Granular control, cost transparency, works with OpenCode.

The OpenCode TUI¶

What: Terminal interface for conversation + file editing + commands

Layout: - Top: Message history - Bottom: Input box - Right: Mode switcher [plan | build]

Key shortcuts: - Enter — Send prompt - Tab — Switch modes - Ctrl+C — Interrupt - Ctrl+L — Clear screen

The Two Modes¶

Plan Mode¶

Read-only
Can investigate, ask questions
No approval prompts
Safe to explore

Build Mode¶

Full access (read, edit, run bash)
Will ask approval for dangerous ops
Use after planning
For making changes

Workflow: Plan first → Build second

The `/init` Command¶

What: Analyzes your project and generates AGENTS.md

What AGENTS.md contains: - Project type (Node.js? Python? Rust?) - Key directories (src/, tests/, docs/) - Code style conventions (Prettier? ESLint?) - What NOT to do (boundaries)

Why: Agent knows your project without you describing it every time

How to use it: Type init in OpenCode input, press Enter

What AGENTS.md Looks Like¶

# Project Conventions for [Project Name]

## Context
This is a Node.js application for [purpose].

## Key Directories
- `src/` — Source code
- `tests/` — Test files (Jest)

## Conventions
- Code style: ESLint + Prettier
- Testing: Jest (npm test)

## Out of Bounds
- Do not modify package.json
- Do not run npm install without asking

After /init runs: Read it aloud. Did the agent understand your project?

Your First Task¶

Scenario: Fix a typo in src/index.js - Wrong: consoel.log() - Right: console.log()

Steps: 1. Install OpenCode 2. Get API key (Anthropic or OpenAI) 3. Set ANTHROPIC_API_KEY env var 4. Run opencode 5. Ask agent to find the typo (plan mode) 6. Ask agent to fix it (build mode) 7. Verify: grep console.log src/index.js

Cost & Budget¶

For this 10-week course: - Weeks 1–3: ~$2–3 - Weeks 4–6: ~$5–10 - Weeks 7–10: ~$10–20 - Total: ~$20–30

Model choice matters: - Sonnet (Anthropic): Cheaper, good enough - GPT-4o (OpenAI): More expensive, faster - Ollama: Free, less capable

Pro tip: You can swap providers mid-course.

Common Questions¶

Q: Can I use OpenCode without an API key? A: Yes, with Ollama (local, free). Less capable but works.

Q: Do I pay for every keystroke? A: No. Only when you press Enter and send a prompt.

Q: What if I'm offline? A: Use Ollama. Download a model on another machine, then serve it locally.

Q: Can I switch providers later? A: Yes. Just change the env var (ANTHROPIC_API_KEY ↔ OPENAI_API_KEY).

Week 2 Labs¶

Lab 2.1: Install OpenCode + provider key. Fix a typo end-to-end.

Lab 2.2: Run /init on a real open-source project. Read AGENTS.md aloud.

Reflection: When did the agent get it wrong? Why?

Next Week: Plan vs. Build¶

In Week 3, you'll learn to use plan mode deeply: - How to explore codebases safely - When to stay in plan mode (code review, audits) - How to write better prompts for exploration

For now: Install. Get a key. Run your first task.