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

Annotations already declare read-only, open-world, non-destructive, non-idempotent. The description adds substantial context beyond that: provenance returned, SI unit normalisation, no API key required, explicit rate limits (60/hour, 300/day per IP and session), quota fallback behaviour, and licence warnings.

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 data-format details are front-loaded in the first two sentences, with rate limits and provenance after. It is somewhat long and includes a low-value promotional sentence ('TerraMCP is a Wrench AI service'), but no sentence is severely wasteful.

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 usefully notes that source data and provenance are returned and units are normalised to SI. Rate limits, auth model, and date-range limits round it out; only the exact return shape remains unspecified, which is acceptable.

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 schema already documents station_id, data_type enum, and the start/end date constraints. The description restates the same enum meanings and date window rather than adding syntax or edge-case detail, so 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: fetch NRFA daily flow or catchment rainfall observations for historical catchment analysis. It also disambiguates 'station_id' as a numeric NRFA gauge identifier, not an EA station ID, which separates it from sibling tools like ea_hydro_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 clear invocation context (station_id, data_type codes, ordered YYYY-MM-DD dates within 366 days) and states open-data access with anonymous limits. It does not, however, say when to prefer this over nrfa_station_info or other series siblings, so 'when-not' guidance is missing.

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