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

Annotations already cover read-only/open-world/idempotent status, but the description goes well beyond them: return content ('source data and provenance'), unit normalisation to SI, no API key requirement, explicit rate limits (60/hour, 300/day per IP and session), quota fallback behaviour, and licence warnings. That is substantive operational context an agent cannot get from the annotations.

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 routing are front-loaded in the first two sentences, and the operational details are densely packed. The branding sentence ('TerraMCP is a Wrench AI service') is pure filler, which keeps it from a 5.

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?

There is no output schema, but the description states what is returned (source data and provenance) and covers auth, rate limits, quota fallback and licensing. For a 4-parameter spatial lookup this is complete enough to call correctly.

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 a meaningful qualifier the schema lacks: coordinates must be *confirmed* WGS84 values and the measurement parameter is fixed to rainfall (i.e. no parameter selection exists). It adds value without duplicating the schema verbatim.

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 names a specific verb and resource ('Find nearby EA rainfall gauges and their measures') and scopes it ('rainfall-only monitoring'). It explicitly contrasts with the sibling flood_find_stations, so an agent can route 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 states when to use this tool ('rainfall-only monitoring') and when not to, naming the alternative ('Use flood_find_stations for river level, flow or mixed station discovery'). The precondition that coordinates must be confirmed WGS84 lat/lon is also given.

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