Tool call
The model's structured request to do something in the world — Bash("rm -rf …"), Read("/etc/passwd"), an HTTP fetch, a database query — emitted as a name plus arguments for the host to execute. It is the moment intent becomes effect, which makes it the highest-value point of control in the whole stack: the model layer decides what an agent wants, the tool layer decides what it can, and only the second is enforceable.
See also action layer · PreToolUse hook · MCP
Related terms
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Action layer
Agents & architecture
The enforcement surface at the tool call, as opposed to the prompt layer, which tries to classify text before the model sees it.
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PreToolUse hook
Agents & architecture
A callback the agent host invokes after the model has requested a tool call but before the call executes, handing over the tool name and arguments and…
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MCP
Agents & architecture
An open protocol, introduced by Anthropic in 2024 and now broadly adopted, that standardises how agents connect to external tools and data sources.
Agents & architecture
Where the attacks above actually land. The vocabulary here is worth precision, because the difference between "the model decided" and "the tool ran" is the difference between a risk and an incident.