Agents and tools

An agent is a model loop that can call tools (APIs, shell, retrievers, browsers), observe results, and continue until it stops or abstains. Classic framing: ReAct (reason + act) (Yao et al., 2022).

Agent tool loop

Why tools

Pure next-token prediction invents facts. Tools ground actions:

search / retrieve
code execution
calendars, tickets, payment APIs (dangerous — gate hard)
compile / dump / expect in a Spark world

Failure modes (engineer checklist)

Failure	Mitigation
Invented tool names/args	Strict schemas; validate
Infinite loops	Step budgets; circuit breakers
Unsafe side effects	Dry-run; allowlists; human gate
Prompt injection via tool output	Treat tool text as untrusted
“Looks done” without evidence	Expect / tests / journals

Spark surface

Language: with tools [&] — see programming guide / function catalog.
Behavior + tool loop diagram: docs/images/diagram-behavior-tool-loop.svg
Model aspects tools row — Model aspects
Dry tools return stub:local until live gated.

sequenceDiagram
         participant U as User
         participant M as Model
         participant T as Tool
         U->>M: goal
         M->>M: reason
         M->>T: act
         T->>M: observe
         M->>U: answer or abstain

Spark does not claim autonomous ops on production store systems from this hive page — factory + product gates still apply.

Next: Evaluation · Safety · Factory.