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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so safety is covered; the description goes beyond that by disclosing the cost model (free within a daily allowance, then $0.002 USDC per call via x402), which is real behavioral context an agent needs before calling. It stops short of pagination or result-limit behavior.

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?

Two sentences, zero padding, with the functional scope front-loaded and the billing note deferred. Every clause earns its place.

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?

An output schema exists, so return values need not be described; parameters are fully documented in the schema and annotations carry the safety profile. Adding cost and spatial scope makes this largely complete, with only minor gaps around result limits or pagination.

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?

Schema description coverage is 100%, so the schema already documents all five parameters, including the default radius of 20001 km and the YYYY-MM-DD format for starttime. The description only restates the radius/date concepts at a high level and adds no format or constraint detail beyond the schema.

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-free but precise scope: earthquakes filtered by a point-radius and a start date. This distinguishes it from the fixed-window siblings (earthquakes__m25-day, m45-week, significant-week) and from earthquakes__count/event, but it never names or contrasts with them explicitly.

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?

The phrasing 'within a radius of a point since a date' implies the spatial-proximity use case and implicitly separates it from the time-window siblings, but there is no explicit when-to-use statement, no named alternative, and no exclusion guidance.

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