Custom Runtimes

Explains the case for a hand-rolled runtime when frameworks add more overhead than value, and when that choice is rational rather than not-invented-here.

Learn to build framework-free agent runtimes with 8 Python examples. Define tools, call chat APIs, dispatch tool calls, and enforce turn limits.

Build a ReAct loop as an HTTP API service in FastAPI or Express. Learn to define schemas, implement tools, and wrap the loop for robust agent execution.

A recipe for a pluggable tool-registration system inside a hand-rolled agent runtime, with schemas, allowlists, and safe dispatch.

Ten-plus practices for keeping a hand-rolled agent runtime maintainable as it grows: budgets, plugins, evals, observability, and exit discipline.