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

Annotations already establish readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds meaningful behavioral context beyond that: telemetry is transmitted only once or twice per day, which warns the agent that the 'current' reading may be several hours old. It also states no auth is required. These are valuable operational details that the annotations do not provide.

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. The action and return fields are front-loaded, the freshness caveat is in the second sentence, and the prerequisite plus licensing data is in the third. Every sentence earns its place and the description remains compact despite covering multiple pieces of information.

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 single-parameter read-only tool with an output schema present, the description is complete: it explains what the tool returns, how to get the input, how fresh the data is, and that no authentication is needed. There is no need to describe return values because the output schema already exists. Nothing an agent needs to call this correctly 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%, and the schema's parameter description already explains what station_no is and instructs the agent to obtain it from sepa-scotland.stations_search. The description repeats this prerequisite but adds no new meaning beyond the schema, so the baseline of 3 is appropriate.

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?

The description opens with a specific verb-and-resource pair: 'Get the latest telemetered rainfall reading for one SEPA gauge station by station_no.' It clearly states the scope (one station, current/latest) and enumerates the return fields (value in mm, timestamp, accumulation window, station name/coordinates), which distinguishes it from sibling tools like sepa-scotland.rainfall.history and sepa-scotland.rainfall.stations without needing to inspect their schemas.

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?

The description gives an explicit prerequisite: 'Call sepa-scotland.stations_search first to find a station_no.' This tells the agent exactly how to obtain the required input. However, it does not explicitly name the alternative for historical data (sepa-scotland.rainfall.history), so the when-not-to-use guidance is left to inference from the tool name rather than stated.

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