LLM ToolsA learning lab

Field guide / 02

Give an agent a workspace

A coding harness connects a language model to your project, tools, and review process. Here is how to make that connection useful.

4 minute read · Reviewed October 2026

Model, agent, harness: what is the difference?

The model proposes
It interprets the context and generates text or a request to use a tool. It does not have access to your project unless an application provides that access.
The agent works through the task
It uses a model to choose actions, reads the tool results, and decides whether to continue, change approach, or finish.
The harness runs the process
It manages context, tools, permissions, and session state. A coding harness can connect the agent to files, a terminal, version control, and a browser.
You define and review the result
The editor and diff view help you inspect the work. Tests and a working preview provide evidence that the change meets your request.

Product boundaries vary: an editor can include a harness, and the same agent can appear in several interfaces. Compare the capabilities you need, not just the label on the product.

A useful loop for project work

  1. Brief. Describe one change, the relevant files, the audience, and how you will know it works.
  2. Inspect. Have the agent read the existing project and explain the intended approach when the task is complex.
  3. Build. Keep the work within a reviewable scope. Notice unexpected files, dependencies, or commands.
  4. Verify. Review the diff, run the relevant checks, and try the changed behavior yourself.
  5. Keep. Commit the useful change with a clear description. Record any remaining limitation.

Use a disposable practice project first. Review tool permissions before connecting private repositories or external accounts. A successful test checks a specific behavior; it does not establish that every part of an application is correct.

Explore the tools and their documentation

These are examples to investigate, not a ranking. Features, access requirements, and pricing change; use the official documentation for the version you are working with.