open_meteo_weather$0.002 per call — Current weather from Open-Meteo (no API key, no signup). Given lat/lon returns temperature (C), apparent temperature, humidity, wind speed, precipitation and a WMO weather code. Params: lat, lon (required).
| Name | Required | Description | Default |
|---|---|---|---|
| lat | Yes | Latitude | |
| lon | Yes | Longitude |
Changes observed during successful MCP inspections.
Input schema / properties / latAdded value: +{
+ "description": "Latitude",
+ "type": "number"
+}Input schema / properties / lonAdded value: +{
+ "description": "Longitude",
+ "type": "number"
+}Input schema / properties / qRemoved value: -{
- "description": "JSON or key=value input for the tool",
- "type": "string"
-}Input schema / requiredAdded value: +[
+ "lat",
+ "lon"
+]Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden and does well: it discloses cost ($0.002 per call), the auth profile (no API key, no signup), and the payload contents. It omits error behavior, rate limits, data freshness/caching, and units for wind speed and precipitation.
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 price and source, then the return contract, then the required params — a sensible order with almost no waste. The closing 'Params: lat, lon (required)' largely duplicates the schema and could be dropped.
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 two-parameter read tool with no annotations and no output schema, the description covers cost, auth, input contract, and return fields, which is nearly everything an agent needs. Missing units and error/timeout behavior are the only real gaps.
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, so the schema does the heavy lifting; the description merely restates that lat and lon are required. It adds no coordinate convention (WGS84, decimal degrees) or valid ranges beyond 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 resource and scope ('Current weather from Open-Meteo') and enumerates the returned fields (temperature, apparent temperature, humidity, wind speed, precipitation, WMO code). The 'current' qualifier implicitly separates it from forecast/historical variants, though no sibling is named for routing.
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?
Usage is implied by 'Current weather' plus 'Given lat/lon', so an agent can infer it is the tool for current conditions at a coordinate. There is no explicit when-not-to-use, no alternative named, and no mention of forecast/historical coverage limits.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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