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

Annotations already declare readOnly, destructive=false, openWorld, and non-idempotent. The description adds two useful facts beyond them: authentication is required and results are returned as normalised SI values with source provenance. It does not explain the non-idempotency, rate limits, or pagination.

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?

Only two sentences, but the first is tautological filler that repeats the tool name, and the informative content is thin. It is short due to under-specification rather than genuine conciseness.

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, 0% parameter coverage, four required fields, three enums, and a rich sibling set, the description leaves an agent without the information needed to select or correctly invoke the 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?

Six parameters at 0% schema description coverage and the description names none of them. It says nothing about station_id, property, start/end formats, period granularity, or the statistic enum, so it fails to compensate for the total coverage gap.

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 largely restates the tool name ("TerraMCP authenticated router: ea_hydro_series") and adds only "Returns normalised SI data and source provenance." It never states the actual resource, namely hydrological time series for Environment Agency stations, so an agent cannot distinguish it from siblings like nrfa_get_timeseries or usgs_daily.

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?

There is no when-to-use guidance and no mention of alternatives, despite several overlapping time-series siblings (nrfa_get_timeseries, usgs_daily, flood_get_readings). The only context is "authenticated," which is not usage routing.

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