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 adds non-obvious operational context the agent cannot get elsewhere: refresh cadence ('fetched about every 30 minutes') and that each part carries as_of and the official source, which tells the agent how to judge data staleness.

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-loads the resource and freshness, then the payload contents, then the selector parameter. Every sentence carries information; the trailing example input is mild redundancy given the schema already shows the enum and default.

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?

No output schema exists, but the description compensates by naming the returned sections, their fields, and the as_of/source metadata. For a zero-required-parameter read-only tool this is close to fully sufficient; only exact field-level shapes are left implicit, which is reasonable.

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 coverage is 100% and the enum parameter already documents each value and the default, so the description largely restates what the schema provides. The one small addition is the framing of 'psi' as haze/air-quality readings, but that meaning is already present in the schema's parameter description.

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 resource and verb ('Latest NEA readings for Singapore') and enumerates exactly what is returned: 24-hour weather forecast fields by region/period and 24-hour PSI/PM2.5 with the air quality descriptor. No sibling in the list covers weather or air quality, so there is no ambiguity to resolve.

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?

Gives clear context for when to use each mode ('weather' for forecast, 'psi' for haze/air-quality) and states the default when omitted, plus a concrete example input. There are no competing sibling tools, so the absence of explicit exclusions is not a meaningful gap.

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