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

With annotations already covering the safety profile (readOnly, idempotent, non-destructive, closed-world), the description adds substantive behavioral detail: aggregation only, a five-lender minimum per bucket, metrics of min/avg APR and distinct-lender count, and the latest fresh FreeRateUpdate snapshot as the data source. There is no contradiction with the annotations.

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?

The description is two sentences and front-loads the core purpose before adding scope and exclusion details. Every clause earns its place by clarifying output metrics, aggregation limits, or the data source.

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?

For a parameterless read-only tool with no output schema, the description adequately explains the return shape (min/avg APR and distinct-lender count per product bucket), the aggregation constraint (minimum five lenders), and the data freshness source. Annotations cover the safety semantics, leaving no critical gap for correct invocation.

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 zero parameters, so the schema already fully describes the input. The description adds no parameter meaning because there are none, which matches the baseline of 4 for a parameterless tool.

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?

The description states a specific verb (summary) and resource (network-aggregate advertised-rate), plus the exact metrics returned and the per-bucket lender threshold. It also distinguishes this tool from per-lender siblings with the phrase 'Aggregates only — no per-lender rates.'

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?

It gives clear context that this is for network-aggregate data and excludes per-lender rates, which tells the agent when not to use it. However, it does not explicitly name an alternative tool such as get_mortgage_rates or get_lender_score for per-lender requests, so the guidance stops short of fully routing the agent.

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