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

Annotations already declare readOnly/openWorld/non-destructive, so the safety profile is covered. The description goes well beyond them with auth requirements ('no API key or signup required'), explicit rate limits (60/hour, 300/day per IP and session), anonymous fallback after quota, licence warnings, and unit normalisation to SI.

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 and the sibling routing are front-loaded, and the operational details (limits, licensing, units) are genuine context rather than filler. It is slightly long, and the 'TerraMCP is a Wrench AI service' branding sentence contributes little to tool selection.

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 tool with no output schema, the definition supplies everything an agent needs: what is returned ('source data and provenance'), the unit convention, auth/quota behaviour, and the sibling to use for observations. No material gap remains.

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% and the single parameter is fully documented in the schema. The description only restates that station_id is numeric, adding no format or edge-case detail beyond the schema's own 'not an EA station ID' note, so the 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?

Opens with a specific verb and resource ('Get NRFA gauging-station metadata, river, location and catchment area') and states the purpose (identify a historical flow record). It explicitly distinguishes itself from the sibling nrfa_get_timeseries, so an agent can route without opening either 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?

Names the alternative tool and the condition that selects it: 'use nrfa_get_timeseries for observations', implying this tool is for station metadata rather than time series. The required input ('Supply the numeric NRFA station_id') is stated up front.

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