The most expensive mistake in agent work is using an agent where a script belongs. It is also the most common one, because agents are exciting and scripts are not. This article offers four questions that settle it, and the evidence from this rig's own decisions.
The four questions
Is it ambiguous? If the input varies in ways rules cannot enumerate — a messy brief, an unclear spec, a weird repo state — judgment is required, and that is an agent's home turf.
Does it repeat? Same input, same output, every time. Repetition is a script's home turf. An agent on a deterministic job burns tokens for variance you did not want.
What does failure cost? Cheap failure (a draft nobody ships, a suggestion nobody takes) tolerates agents. Expensive failure (payments, publishing, anything client-facing) needs deterministic paths and guardrails.
Who must audit it? If a decision needs to be traced after the fact — compliance, billing, client disputes — you need either normal code or a fully logged agent with provenance attached.
A decision in sequence
The measured before and after
The hybrid pattern that usually wins
Most real work is a script with an agent at the edges: deterministic pipeline for the 90% that repeats, agent for the 10% that needs judgment, with the handoff explicit.
Where to go next
This site's own routing system is a working instance of the hybrid pattern: cheap workhorse for routine work, frontier escalation only when the questions above say the judgment is real.
- The multi-agent journey — the architectural history behind this heuristic
- Proof, not prompts — how auditability attaches to whatever you choose