Running & Testing Locally

From Reading to Doing

In Block 1, Claude read your code and explained it. That was impressive — but Claude Code is not just a reader. It’s a doer.

This block is where things get real. Claude will run npm install, start your dev server, execute your test suite, lint your code, and build a Docker image. And when something breaks — because we’re going to break something on purpose — Claude will diagnose the error, figure out the fix, and apply it.

This is the Bash tool in action: Claude’s ability to execute shell commands in your terminal, with a safety-first permission model that makes sure you’re always in control.

What We’ll Cover

1. The Bash tool — how Claude executes commands and reads their output
2. The permission model — why Claude asks before running things, and how to manage it
3. Project setup — npm install and npm run dev via Claude
4. Testing and linting — running the full quality pipeline
5. Docker builds — multi-stage image building
6. Error handling — the break-and-fix exercise
7. Context management — using /clear and /compact

The Permission Model

Here’s something important: Claude Code does not just run commands willy-nilly. When Claude wants to execute a shell command, it asks you first. You’ll see a prompt like:

Claude wants to run: npm install
Allow? (y/n)

This is intentional. Claude is powerful, and power requires guardrails. You stay in control of what actually executes on your machine. Over time, you’ll develop a rhythm — approve routine commands quickly, pause and think about unfamiliar ones.

You can also configure which commands are auto-approved and which always require confirmation. We’ll cover that customization in later blocks.

Context Management: /clear and /compact

As your conversation grows, Claude’s context window fills up. Two commands help manage this:

• /clear — nuclear option. Wipes the entire conversation and starts fresh. Use this when you’re switching to a completely different task.
• /compact — smart option. Claude summarizes the conversation so far into a compressed form, freeing up context space while retaining the key information. Use this when you’re deep into a long session and Claude starts feeling slow.

Think of /clear as closing all your browser tabs and starting over. /compact is more like bookmarking the important tabs and closing the rest.

Choose Your Format

Pick the format that matches how you are using the block: