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

Annotations already cover safety (readOnlyHint true, destructiveHint false, openWorldHint true), and the description adds genuinely new context: returned source data with provenance, SI normalisation of hydrological units, anonymous rate limits (60/hour, 300/day) with key fallback, and licence warnings. It stops short of describing response shape or how 'latest' ordering is determined, so not a 5.

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 purpose and routing before operational details, and most sentences carry real information. The 'TerraMCP is a Wrench AI service' line and the trailing licence boilerplate are mildly extraneous but defensible provenance.

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 compensates by stating what is returned (source data and provenance) and how values are normalised, plus auth and rate-limit constraints. An agent has everything needed to call this correctly against a 2-parameter, read-only tool.

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 both parameters are already documented by the schema, and the description largely restates them ('latest_n is per measure'). It adds the useful provenance hint that station_id comes from flood_find_stations, but no new format or semantic detail. Baseline 3 applies.

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 ('Get recent observations across an EA station's measures') and scopes it to inspecting current conditions. It is clearly separable from sibling readers such as rainfall_latest, nrw_readings and sepa_values by naming the EA station measure scope.

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?

Explicitly routes the agent: station_id must come from flood_find_stations, and rainfall-only queries should use rainfall_latest instead. It also sets a boundary on interpretation ('Observations are not forecasts or design levels'), covering when-not usage.

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