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

Annotations already cover read-only and world-open behaviour, so the bar is lower; the description still adds real value with anonymous rate limits (60/hour, 300/day per IP and session), keyed fallback, no-signup, SI normalisation and licence warnings — behaviour genuinely not captured in annotations. Docked one point for the 'TerraMCP is a Wrench AI service' marketing filler, which is not behavioural context.

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 constraints are front-loaded, which is good, but the tail drifts into vendor boilerplate and licensing legalese. The rate-limit sentence earns its place; the 'TerraMCP is a Wrench AI service' clause does not.

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, and the description compensates by noting it returns source data and provenance (with SI normalisation). With annotations covering safety and the schema covering all four parameters, an agent has what it needs to call this correctly; only the return shape remains loosely specified.

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 the baseline is 3. The description restates the parameter codes and the 'optional USGS- prefix' that the schema already documents, adding the 366-day pair constraint but nothing the schema lacks.

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') plus resource and scope ('USGS daily mean discharge, stage or water temperature for historical US monitoring analysis'), and the USGS source cleanly separates it from the NRFA/SEPA/EA/NRW siblings that also serve hydrology series.

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?

Gives a context ('historical US monitoring analysis') and the parameter code mapping, which implies when to reach for it, but never states when-not to use it or names an alternative tool. Usage is implied rather than prescribed.

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