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

With no annotations, the description carries the full burden and largely succeeds: it discloses the data source ('nearest live Open-Meteo relay within 75 km'), a signed receipt, the per-call price ($0.001), and a free tier (first 3 priced calls per caller). It does not cover failure modes (e.g., what happens when no relay is within 75 km) or auth specifics, keeping it short of 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?

Front-loaded with the core purpose and returned fields, then invocation, then pricing. Two compact sentences plus two short pricing clauses, each earning its place by conveying field/unit, source scope, cost, and quota information.

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 3-param tool with no annotations and no output schema, the description effectively supplies the return-value picture by listing the four measurement fields and units, along with source, cost, and quota. The main remaining gap is error/miss behavior when no relay falls within the radius.

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 a 3 is the baseline. The description adds genuine meaning beyond the schema by framing city and coordinates as alternatives ('Pass latitude and longitude, or a city'), a mutual-exclusivity relationship the schema does not encode; it also ties the result to a 75 km proximity constraint.

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 ('Current weather at a place') and enumerates the exact returned fields with units (temperature °C, humidity %, pressure hPa, wind m/s). The naming of the data source and 75 km radius / signed receipt scope makes it clearly distinguishable from siblings like air_quality_now and nearby_sensors.

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 description tells the agent how to invoke it ('Pass latitude and longitude, or a city') but gives no guidance on when to prefer it over air_quality_now, nearby_sensors, or other weather-adjacent siblings, nor any exclusion conditions. Usage is implied by the resource name rather than stated.

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