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

With no annotations present, the description carries the full burden. It communicates a read-only lookup ('Get current weather') but adds no context about response nature, caching, rate limits, or lack of side effects. The word 'current' does clarify real-time conditions as opposed to forecasts.

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 wording is tight and front-loaded, but the '[COST: ]' prefix is an unresolved placeholder that adds noise without information. Otherwise, the description is one efficient sentence.

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 zero-parameter tool with an output schema, the description covers the essential action but omits usage context and any note about the missing cost field. The presence of many sibling weather tools makes the lack of routing guidance more noticeable.

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 input schema is empty, so the description does not need to document parameters. There are zero parameters to describe, and the baseline for no-parameter tools is 4.

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 explicitly states the operation ('Get') and resource ('current weather in Tokyo'), which clearly distinguishes it from sibling city weather tools. The only ambiguity is the empty '[COST: ]' prefix, which is a placeholder rather than meaningful content.

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 provides no explicit guidance about when to use this tool over alternatives such as get_paris_weather or get_london_weather. The intended context is implied by the Tokyo city in the name and description, but no exclusions or alternative routing are stated.

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