Skip to main content
The Tools view shows every tool your agents have called, aggregated across all traces. Use it to find slow tools that bottleneck agent performance, high-failure tools that need fixing, and underused tools that may indicate agents are routing poorly.
Zespan tools view showing tool call counts, failure rates, and latency breakdown

​
Tool list

The tool list shows all tools called in the selected time range:
ColumnDetails
Tool nameThe tool identifier from the SDK span
CallsTotal invocation count
Failure ratePercentage of calls that returned an error
Avg latencyMean duration per call
AgentsHow many distinct agents called this tool
Last calledTimestamp of the most recent call
Sort by failure rate to prioritize reliability work. Sort by avg latency to find performance bottlenecks.

​
Tool detail

Click any tool to open its detail page.

​
Call history

A paginated list of recent calls with timestamp, agent, input arguments (if storePrompts is enabled), return value summary, latency, and outcome.

​
Latency distribution

A histogram of call durations. A bimodal distribution (two peaks) often indicates cache hit vs cache miss behavior or fast vs slow execution paths.

​
Calling agents

A ranked list of agents that call this tool, with per-agent call counts and failure rates. If one agent has a much higher failure rate than others calling the same tool, the issue is likely in how that agent constructs the tool arguments.

​
Tool span types

Zespan records tool calls as spans of kind tool. Retrieval operations (vector search, document fetch) are recorded as spans of kind retriever. Both appear in the Tools view. See Span kinds for the full list of span types and what each captures.

​
Registering tools in code

Tools appear automatically when your agent makes calls that the SDK recognizes as tool spans. For custom tools, wrap the tool function with a manual span: 
import { startSpan } from "@zespan/sdk";

async function searchDatabase(query: string) {
  return startSpan({ name: "search-database", kind: "tool" }, async (span) => {
    span.setAttributes({ "tool.input": query });
    const result = await db.search(query);
    span.setAttributes({ "tool.output.count": result.length });
    return result;
  });
}
See Manual spans for full span API reference.

​
Next steps