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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, which covers safety. The description adds useful context beyond the annotations: the data is real-time, comes from api.weather.gc.ca (MSC GeoMet OGC API - Features), and requires no authentication. There is no contradiction between the description and 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 well-structured sentences with no filler. The core action and conditional behavior are front-loaded, and the source/auth details are placed at the end without distracting from the main usage. 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?

With an output schema present, the description need not explain return values. The description covers the two optional parameters, the default behavior when location_id is omitted, the data source, and authentication requirements. An agent can successfully call this tool with just the description and schema; only a full station list for discovering location_id would be extra, but the example value provides enough guidance.

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%, and both parameters (limit, location_id) have detailed descriptions including defaults, range, and an example value. The tool description adds no parameter meaning beyond the schema, matching the baseline 3 for high coverage. It neither clarifies nor contradicts 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?

The description uses a specific verb, "Get real-time Air Quality Health Index (AQHI, 1-10+ scale) observations," and clearly identifies the resource and scope (Canadian monitoring location or all of Canada). It is clearly distinct from sibling msc-geomet tools (climate.daily, climate.stations, hydrometric.realtime) by subject, but it does not explicitly name an alternative, so it falls short of fully explicit sibling differentiation.

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 clearly states the two usage modes: provide location_id for a single location, or omit it to get the latest reading from every monitored location. It also notes the data source and no-auth requirement. However, it does not explicitly tell the agent when NOT to use this tool or point to an alternative (e.g., msc-geomet.climate.stations for station metadata), so no exclusions are given.

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