GenAI Field Guide

Agents and beyond

API vs. the web interface

The web interface is the vendor's harness, the vendor's preamble, one human, one conversation. The API is your code sending the prompt and receiving the reply, with everything else up to you.

≈1 minLandscape facts checked — re-verify before relying on them.
Web app The vendor sets thedefaults API Your code runs theworkflow Vendor setup Preamble · tools ·conversation Your setup System prompt ·tools · loops Interactive use One person · oneconversation Your checks Logs · validation ·token costs
Full control, no rails, pay per token.

What the API gives you, and costs you

You gain You lose
Your own system prompt and tools The vendor's safety rails and conveniences
Fixed output formats (JSON schemas) and lower creativity settings The chat's memory, projects, and file handling
Ten thousand calls in a loop, batches, logging Simplicity; you pay per token and own every failure
Deterministic code between steps, the pipeline pattern Nothing else; this is the point