What is Harness?
The product code that runs a model on a task: the loop, tools, context, permissions and memory that turn single replies into finished work. Agentic loops work when a capable model meets a good harness; neither is enough alone.
weld · inspect · rework · pass
In an agent product, the harness is…
Write it in your own words in the app.
In real work
The new model helped, but the bigger jump came from the harness: the coding agent now runs the tests, reads the failures and tries again before replying.
In the illustration
Inside the cell the arm welds a seam, the camera inspects it and flags a gap, and the cell sends the arm back to rework it. On the second pass the inspection light turns green.
Sketch the harness for our coding agent in your model: the loop, the tools it can call, how it reads test failures and retries, and when it must stop and ask a person.
Try it now
The fastest way to learn a word is to use it. Open this line in the agent you already work in and watch what it does. Change the tool to the one you use.
Go further
01Practice
Make it stick
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02Verify
Prove you know it
Pass the quiz and keep it in a Skills Wallet you can share with anyone who needs proof.
03Career
Find the work that uses it
See which roles lean on this vocabulary, and what they pay in year one.
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