AI Foundationspredict · compress · act

concepts → Mechanism

Mechanism

Tool use

also called function calling

decade9 connections

the model asks for a function to be run, and reads the result back

Where it sits

The prism has six jobs across and eight layers down. Its primary cell isact × L6. Hatched cells cannot exist — a GPU does not learn, an institution does not infer.

What must come first — and what it unlocks

Left to right is reading order, derived from the prerequisite_of edges. Nothing here is hand-ordered: the diagram is the graph.

nothing comes first — this is a starting pointTool useAgentModel Context Protocol

Unlocks: Agent · Model Context Protocol

What kind of thing it is — and what it is made of

It is made of: Tool schema, Code execution, API, Computer use.

How it goes wrong — and what answers that

known failure modes
Prompt injectioninstructions hidden in content the model reads, obeyed as if you had typed them

Where to read it

The chapter that introduces it, and any chapter that uses it again.

34Hands and Function Callsact 8 · The Agent Infrastructure

Where it comes from

Every connection

All 9 edges touching this node, grouped by relation family — the sections above are highlights from this list. Colours match the relation families inthe atlas.

Structure · 4
has as a partTool schemaFormat
has as a partCode executionMechanism
has as a partAPIProtocol
has as a partComputer useMechanism
Order · 2
must come beforeAgentSystem
must come beforeModel Context ProtocolProtocol
Flow · 2
is used byAgent harnessSystem
Failure · 1
fails byPrompt injectionFailureMode

This page is a projection of one node in src/data/concepts.ts. It has no prose file of its own — 230 declared edges produce all 236 of these pages. Edit an edge and both endpoints change.