The question: What turns a model into a product?
The model never changes, the harness does
A model with no harness is an expert shut in a phone box: it can advise you, it cannot touch anything. The harness is the workstation you set up around it, and it always assembles the same four organs: access (what it can see), tools (what it can do), rules (how it is to work) and guardrails (what limits the damage).
One point the diagram makes visible: in the whole of this workstation, only one part is probabilistic, the model. All the rest is ordinary software, deterministic. Change workstation and watch: the model does not move, its capabilities do.
What this workstation can doIt answers you, and that is all. It looks nothing up and does nothing.
01Guardrailsdeterministic
What limits the damage when things go wrong.
Empty
02Rulesdeterministic
The standing instructions: the tone, the procedures, the prohibitions.
Empty
03The modelprobabilistic
The only probabilistic part of the workstation. Identical in all four cases: not one weight changes.
Constant
04Toolsdeterministic
What the model can do.
Empty
05Accessdeterministic
What the model can see.
Empty
The journey of a request
The same workstation, seen over time. The harness runs, the model decides.
Glossary terms
- harness
- large language model
- tool
- context
- prompt
- agent
- assistant
- tool calling
- MCP
- API
- guardrails
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