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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and openWorld, so the safety profile is covered by structured data. The description adds useful context the annotations do not: it hits a live external service (Open-Meteo) and costs nothing. It does not disclose units, timezone handling, forecast granularity, or failure behavior for out-of-range coordinates.

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?

A single dense line, front-loaded with the resource and scope, with no filler. It is arguably too compressed rather than too long — the brevity is a coverage problem, not a waste problem, so structure is rewarded but not perfect.

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 2-parameter read tool with full schema coverage and rich annotations, most of what an agent needs is already present elsewhere. However, there is no output schema, so the description is the only place to signal what actually comes back — units (C vs F), temperature vs precipitation fields, and how the 3-day portion is structured are all absent.

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%, with both lat and lon documented including format, valid ranges, and worked examples, so the schema does the heavy lifting. The description only names 'lat/lon' and adds no format, ordering, or rounding constraints beyond it. Baseline 3 applies.

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 the resource (weather), the scope (current conditions plus a 3-day range), the input domain (lat/lon), and the upstream provider (Open-Meteo). The phrase '3-day range' is slightly ambiguous — it reads as a 3-day forecast but never says 'forecast' — which keeps it short of a 5. No sibling operates in this domain (fx_rates, validate_iin, track_parcel), so no differentiation is required.

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?

There is no when-to-use or when-not-to-use guidance at all — no mention of whether it is meant for a point lookup versus a listing's location, no prerequisite or fallback. The only decision-relevant cue is the trailing 'Free.', which hints at cost but does not route the agent to any alternative.

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