Most "how to use Claude" advice splits into two camps: people who live in claude.ai for writing, and people who only touch the API to build something. I use both, plus Claude Code, and they solve genuinely different problems — treating them as interchangeable is where most of the frustration comes from.
claude.ai is where thinking happens — drafting an article, working through a framework, arguing with myself about whether a use case is actually worth building before I touch a line of code. Projects and long context mean I can keep an entire line of thinking in one place instead of re-explaining the background every session.
Claude Code is where building happens — it reads the actual codebase, runs the actual build, and iterates against real output instead of me copy-pasting snippets back and forth between a chat window and my editor. Using plan mode before a large change, and letting it run its own tests and lint, catches mistakes I'd otherwise ship and only notice in review.
The API is where it stops being a conversation and becomes part of a system — an agent that takes a real input, a message, a document, an event, and does something with it. That's where the same identity and scoping discipline I use in agent work generally actually matters, because now it's running unattended.
The single tip that moves the needle more than any other: be as specific about context and constraints as you'd be briefing a new hire, not typing into a search box — what you're trying to accomplish, what "done" looks like, what's explicitly off-limits. Vague prompts get vague output, regardless of which of the three surfaces you're using.
Three tools, three jobs: do the thinking in claude.ai, do the building in Claude Code, do the running in the API. Trying to make one of them do all three is usually where people get stuck.