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

Beyond the readOnly/openWorld/destructive annotations, it discloses that source data and provenance are returned, that hydrological units are normalised to SI, that no API key is required, and specific anonymous rate limits (60/hour, 300/day per IP and session) with key fallback behaviour and licence warnings. This is exactly the extra operational context annotations cannot carry.

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?

Purpose, usage, and return/units information are front-loaded and efficient, and the rate-limit and licence notes are useful. The 'TerraMCP is a Wrench AI service' sentence is branding that does not help the agent and is the main bit of waste.

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 still states what is returned (source data and provenance) and covers auth, rate limits, and unit normalisation. It does not detail the shape of the returned readings, but for a simple 2-param read tool this is nearly complete.

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 value by naming the exact sibling tool (rainfall_stations) that produces a valid station_id, which the schema only refers to generically as 'the corresponding provider's station discovery tool'. It adds marginal meaning on top of 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 (Get), resource (recent rainfall observations in mm), and scope (EA rainfall gauge), and it explicitly routes the agent to rainfall_stations for the station_id. An agent can distinguish this from rainfall_stations, nrw_readings, and tide_readings without opening any schema.

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?

It gives the concrete prerequisite 'Use a station_id from rainfall_stations' and explains the latest_n default, which tells the agent how to drive the tool. It stops short of explicit when-not-to-use guidance or naming alternative reading tools for non-EA regions, so it is clear context without exclusions.

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