agent-wrap-tool

Agent Tool Wrappers

Middleware around an agent's tool execution, the same way client.CallWrapper and server.HandlerWrapper wrap RPCs.

Every tool call an agent makes runs through model.ToolHandler:

type ToolHandler func(ctx context.Context, call model.ToolCall) model.ToolResult
type ToolWrapper func(model.ToolHandler) model.ToolHandler

WrapTool (exposed as micro.AgentWrapTool) registers a wrapper: it takes the next handler and returns a new one. Code before next(...) runs before the tool, code after runs after. That single seam covers the whole lifecycle — before/after hooks, timing, metrics, retries, inspecting results.

What this example does

One flaky weather service and one agent with two wrappers:

• observe — times every call and records a per-tool count, logging the correlation ID (call.ID) carried through from the provider. It observes; it changes nothing.
• retry — re-runs a call whose result is an error, up to three attempts. The weather service fails the first time it's hit and succeeds after, so retry turns a transient failure into a success the model never sees.

Wrappers compose outermost-first: observe is registered first, so it wraps retry and sees one logical call even when retry runs the tool twice.

micro.NewAgent("forecaster",
    micro.AgentServices("weather"),
    micro.AgentProvider(provider),
    micro.AgentAPIKey(apiKey),
    micro.AgentWrapTool(m.observe, retry(3)),
)

Wrappers vs. guardrails

Developer wrappers run outside the built-in guardrails (MaxSteps, LoopLimit, ApproveTool), so they see every call and its result — including a guardrail's refusal. The flip side: a retry wrapper's next is the full guardrail stack, so each retry is also counted by loop detection. Keep LoopLimit at or above your retry count, or set AgentLoopLimit(0) when a wrapper owns the repetition.

See the Agent Guardrails guide for the full picture.

Run

Needs an LLM provider key:

export ANTHROPIC_API_KEY=sk-ant-...   # or OPENAI_API_KEY, GEMINI_API_KEY, ...
go run main.go