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

Annotations cover the safety profile (readOnly, idempotent, openWorld), yet the description adds substantial non-annotation behavior: paid tool via x402 USDC on Base at $0.002 per successful call, and the specific failure mode that calling without payment returns a PaymentRequired object. It also discloses the CC BY 4.0 attribution obligation.

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-loaded with the use case, then return shape, then inputs, then payment/legal terms — a sensible order with no filler. It is a dense single paragraph that runs long, but each clause carries distinct information an agent needs.

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 no output schema, the description fully describes the return payload (current fields, hourly series, daily summaries with min/max, precipitation, dominant symbol). Combined with timezone, licensing, and payment behavior, an agent has everything needed to invoke and interpret the call.

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%, so the baseline is 3, but the description adds genuine meaning beyond the schema: it establishes that lat/lon and place are alternatives ("Give lat/lon, or a place name resolved via Wikidata") and that times are UTC. It doesn't restate bounds or the 1-48 hour range already in 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?

States a specific verb and resource: returns a weather forecast for a location, from a named source (MET Norway) with global coverage. It enumerates the exact payload (current conditions, hourly series, daily summaries), which clearly separates it from siblings like geocode, holidays, and fx_* tools.

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?

"Use for trip planning, logistics, event or outdoor decisions" gives clear positive usage context. It does not, however, name a when-not condition or point to a sibling alternative (e.g. geocode for resolving ambiguous names), so it stops short of full routing guidance.

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