What Is Claude Code? How Agentic Coding Tools Write and Run Code

Most people’s mental model of an AI coding tool is autocomplete: you type, and the model finishes your sentence or your function. Claude Code works differently. Instead of suggesting the next few lines, it’s built to take an instruction — “fix this failing test,” “add pagination to this API,” “refactor this module” — and carry it out: reading the relevant files, writing the changes, running the project’s own commands to check its work, and reporting back what it did. It’s one of the clearest examples of what an AI agent looks like applied specifically to software development.

What Is Claude Code?

Claude Code is Anthropic’s agentic coding tool, built around its Claude models. Rather than living only inside a chat window, it runs where developers actually work — in the terminal, and integrated into popular editors — and it’s given direct access to a project’s files and command line. That access is what separates it from a typical chatbot: it doesn’t just describe what code to write, it opens the files, makes the edit, runs the test suite, reads the output, and keeps iterating until the result actually works.

How It Actually Works

At a high level, Claude Code operates in a loop that looks something like this:

  • Understand the request. It reads the relevant parts of the codebase to figure out how the project is structured before making any changes, rather than guessing based on the prompt alone.
  • Plan the approach. For anything beyond a trivial fix, it works out a sequence of steps — which files need to change, what order to change them in, what might break.
  • Take action. It edits files directly and runs real commands: installing dependencies, running the test suite, checking linter output, making git commits.
  • Verify and iterate. It reads back the results of what it just ran — a failing test, a compiler error, unexpected output — and adjusts, rather than assuming the first attempt was correct.

For larger jobs, Claude Code can also delegate: breaking a big task into pieces and running focused subagents on individual parts of it, which is the same multi-agent pattern showing up across agentic coding tools generally. One agent might explore how a feature is currently implemented while another writes the replacement, with the results combined at the end.

Connecting to the Rest of a Developer’s Tools

A coding agent is only as useful as what it can reach. Claude Code supports the Model Context Protocol (MCP), an open standard that lets an AI agent connect to external tools and data sources — a project management board, a database, a design file, an internal API — in a consistent way, rather than needing a one-off integration built for every single tool a team uses. That matters in practice: it’s the difference between an agent that can only see the code in front of it and one that can check a ticket’s requirements, pull real data to test against, or open a pull request against the team’s actual workflow.

Claude Code vs. Traditional Autocomplete Tools

Earlier AI coding assistants were largely built around suggestion: you write code, and the model predicts a likely continuation, which you accept or reject line by line. Claude Code is built for a different unit of work entirely — not “what’s the next line,” but “finish this task.” That shift matters for how it’s used. A developer might hand it a bug report and walk away, rather than sitting and reviewing every individual suggestion as it’s typed. It’s a meaningfully different workflow from editor-native tools like Cursor, which blend inline suggestions with agent-style edits inside a familiar editor interface, and it sits on the more autonomous end of the spectrum compared to fully hands-off systems like Devin-style agents, which are designed to work through entire tickets with even less back-and-forth.

What It’s Good At

In practice, agentic coding tools like Claude Code tend to perform well on tasks that have a clear, checkable definition of done: fixing a specific failing test, implementing a well-scoped feature, migrating code from one pattern to another across many files, or cleaning up and documenting an existing codebase. Having the model actually run the tests and read the real output, rather than just generating plausible-looking code, is what makes these multi-step jobs more reliable than single-shot code generation.

Where It Still Needs a Human

Agentic coding tools are not a replacement for engineering judgment. A few limits worth knowing:

  • Ambiguous requirements still need a human to resolve. An agent can execute a well-defined task reliably; it can’t read a stakeholder’s mind about what “better” means for a vague request.
  • Review still matters. Code that passes its own tests can still contain design decisions, security issues, or architectural trade-offs a reviewer needs to weigh in on.
  • Knowledge of very recent libraries or internal conventions can be incomplete — the kind of limitation covered in our explainer on an AI model’s knowledge cutoff — which is part of why giving the agent access to the actual codebase and live tool connections, rather than relying on memory alone, makes such a difference.

The Bigger Picture

Claude Code is part of a broader shift in how AI gets used in software development: away from suggestion-based tools that assist a developer typing code, and toward agents that are handed a task and trusted to complete it, checking their own work along the way. It’s one entry in a fast-moving field that includes editor-based tools and more autonomous systems alike — worth understanding in the context of how the major AI labs are each building out their own take on agentic development tools.

The Bottom Line

Claude Code represents a different category from both simple autocomplete and from fully autonomous engineering agents: a tool that reads a codebase, plans a change, makes it, verifies it by actually running the project, and reports back — with a developer still in the loop to review the result. As agentic coding tools mature, understanding that distinction between suggestion, assisted execution, and full autonomy is becoming essential for any team deciding how to bring AI into its development workflow.