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

Annotations already declare readOnlyHint=true, idempotentHint=true, openWorldHint=true, and destructiveHint=false, so safety and idempotency are covered. The description adds useful behavioral detail about the forecast interval (3-hour steps) and the fields returned, but it omits rate-limit behavior and the _apiKey handling already documented in the schema. With annotations carrying the safety profile, a 3 is appropriate.

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 front-loaded with the core purpose and delivers the key fields in one sentence, followed by a compact example. It is efficient and has no wasted sentences, though the example slightly duplicates the schema example.

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?

Given the simple read-only nature of the tool, fully documented schema, and existing annotations, the description is nearly complete. The only material gap is the lack of explicit comparison with current_weather, which would help an agent choose correctly between the two. No output schema exists, so the description is not expected to explain return values.

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 every parameter is fully documented in the input schema. The description reinforces the city/coordinates option and shows an example call, but does not add syntax or semantic details beyond what the schema already provides. Baseline 3 applies when the schema does the heavy lifting.

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 and resource — retrieving a multi-step weather forecast — and enumerates the returned fields (temperature, conditions, wind speed, precipitation probability). It is clear what the tool does, but it does not explicitly differentiate itself from the sibling tool current_weather, leaving the agent to infer that this tool is for future steps rather than current conditions.

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?

Usage is implied through the phrase 'multi-step weather forecast' and the example call, which suggests use when forecast data over time is needed. However, there is no explicit guidance on when to choose this tool over current_weather or how to interpret the required inputs. No exclusions or alternatives are named.

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