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

With no annotations, the description carries the full behavioral burden and does substantial work: it discloses that the tool is paid ($0.003 USDC on Base via x402), names the data provider, and enumerates the forecast horizons and variables returned despite no output schema. Not disclosed are failure behavior for unresolvable places, precedence when both place and lat/lon are supplied, or latency/rate limits.

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?

Three sentences, zero filler, and the most important information (what data, over what horizons) is front-loaded before the input modes and the payment note. The paid-call detail is placed last where it belongs as a caveat rather than a headline.

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 four-optional-parameter read tool with no annotations and no output schema, the description covers what is returned and what it costs, which is enough for correct selection and invocation. It could be more complete by explaining precedence between place and lat/lon and what happens on an unresolvable location, but no critical piece is missing.

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 lat, lon, days and place are all documented in the schema itself, including the 1-10 range and default of 7 for days. The description adds only that place and lat/lon are alternative addressing modes, which the schema already conveys via 'instead of place'. Baseline 3 applies since 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?

States a specific verb+resource ('Weather now and forecast for any place') plus the exact data covered: current conditions, 24-hour hourly, up to 10 days of daily min/max, precipitation, wind and conditions. It also names the upstream provider (MET Norway), so an agent knows the source and coverage without opening the schema. No sibling weather tool exists, so differentiation is unnecessary.

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 invocation guidance: 'Pass a city or address, or lat and lon' establishes the two mutually exclusive input modes, and 'for any place' signals unrestricted geographic scope. It stops short of explicit when-not-to-use conditions (e.g. what to do for historical weather or for a place it cannot resolve), so it is clear context but not full routing guidance.

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