"Which element should the agent click next? Here's the page…"
LLM
Writes its answer as text
2 · Output
Free text
Looking at the page, the best next step is probably the Checkout button, since the cart already has two items. However, you could also go back and…
3 · Extra step
Parser
Your code has to dig the answer out of the text.
Breaks when wording or format changes
Decision
"Checkout"?
If the parser got it right
1 · Input
State + typed question
state: {page: "cart"}
choice:
- Add to cart
- Checkout
- Back
Jev
Picks one of your options, with probabilities
2 · Output
Structured answer
{"choice": "Checkout"}
Checkout0.91
Add to cart0.06
Back0.03
No parsing step
The answer is always one of the options you defined
Decision
Checkout
Your code acts on it directly
Always a valid option, not always the right one. Jev can't return output your code fails to parse, but it can still pick the wrong option. Keep deterministic assertions as your source of truth.
Illustrative example · probabilities are not real Jev output