Index-wide counts

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnly, idempotent and non-destructive, so the safety profile is covered. The description adds genuinely new behavioral context: no API key required on the free tier, zero arguments, and the shape of the response (flat object with snapshotAt, methodologyVersion, etc.). It stops short of noting rate limits or caching of the snapshot, which would have made it a 5.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Purpose and the returned figures are front-loaded, followed by usage and routing guidance. The long enumeration of metrics is justified because it tells the agent what it can quote, though it could be tightened with a grouping phrase.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With an output schema present, the description need not document return values in full, yet it still names the key fields. It covers when to call, what it returns, auth requirements, and the sibling alternative — nothing material is missing for a zero-argument read tool.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The tool takes no parameters, so the baseline is 4 per the rubric. The description confirms this explicitly ('Takes no arguments'), which is the only param-related thing an agent needs to know.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('Get the index's headline numbers') and enumerates exactly which figures are returned, including the snapshot date. It also explicitly distinguishes itself from the sibling pulse_lanes, so an agent can route between them without opening either schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives three concrete use cases (sizing the index, quoting a dated figure, checking data freshness before trusting a grade) and names an alternative tool with the condition that selects it ('use pulse_lanes when you need the lanes themselves'). Nothing is left to inference.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.