C

Claude

Pick

Anthropic's family of AI models and the apps built on them: the Claude chat app, Claude Code for terminal work, and the API.

6 chapters49 tutorialsOfficial site

01 · Introduction

What Claude is

Claude is the name of Anthropic's AI models and of the products built on them.

  • The models come in tiers. Opus is the strongest and most expensive, Sonnet balances quality and cost, Haiku is the fastest and cheapest. Newer generations replace older ones under the same names.
  • Claude.ai is the chat app (web, desktop, mobile). It can read files, search the web, run code and remember your projects.
  • Claude Code is an agent that works in your terminal and editor: it reads a codebase, makes changes, runs commands and opens pull requests.
  • The API lets your own programs and workflow tools call the models.

The same model answers in all of them; what differs is the tools around it.

02 · When to use it

Which Claude for which job

  • Thinking and writing (briefs, analyses, long documents): the chat app with a Project that holds your reference files.
  • Repetitive work on a schedule: the API from a workflow tool, usually with Haiku or Sonnet.
  • Anything that touches code or files on your computer: Claude Code.
  • Connecting Claude to your tools (calendar, docs, databases): MCP servers in the desktop app or Claude Code.

03 · Setup

Getting started

Chat app: sign up at claude.ai. The free plan is enough to learn; Pro adds more usage, Projects and the desktop app features.

Claude Code:

  1. Install Node.js 18 or newer.
  2. Run npm install -g @anthropic-ai/claude-code.
  3. In a project folder run claude and sign in. Ask it to explain the project before asking it to change anything.

API: create a key in the Anthropic Console, add credit, and paste the key into your workflow tool or code. The API handbook shows the first call.

04 · How to use it

Day-to-day use

  • Put the standing instructions in one place: a Project's instructions in the app, a CLAUDE.md file for Claude Code, the system prompt in the API. Claude reads it every time.
  • Give examples of the output you want; one good example beats three paragraphs of description.
  • For long documents, attach the file rather than pasting; the app handles the splitting.
  • In Claude Code, let it run the tests and read the diff before you accept.
  • Use the cheaper model for sorting and summarizing, the strong one for judgment calls.

05 · Pitfalls

Pitfalls

  • Claude can be wrong with confidence. For facts, ask for the source and check it.
  • Chats have a size limit; a very long conversation gets slower and costs more per message. Start a new one when the topic changes.
  • Model names change over time. In automations, use the exact model id from the docs and expect to update it.
  • Claude Code works with your real files. Keep the project in git so any change can be undone.

06 · Resources

Where to go next

The documentation site covers all three surfaces; the tutorials here show them used for everyday work.

My notes

Sign in to keep private notes on this handbook.Sign in