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

Annotations cover the safety profile (readOnly, idempotent, openWorld, non-destructive), and the description adds substantial context beyond them: the full return shape (severity, area, county, river/sea, message text, last-changed, counts by severity) and, critically, the zero-result semantics that separate "nothing is happening" from "the call failed." With no output schema, this is exactly the burden the description should carry.

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?

Front-loaded with the core identity and authority claim, then scope, then return shape, then the edge case. Every sentence carries distinct information (provenance, geography, return fields, empty-result disambiguation) with no filler.

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 fully describes the return payload, the severity taxonomy, the geographic boundary, and the zero-warning case. An agent has everything needed to call it and interpret the result 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%, and the schema descriptions already explain limit, county format, and the min_severity scale including the non-obvious value 4 (include warnings no longer in force). The description adds no parameter-level details beyond the schema, 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 resource (flood warnings/alerts), the exact source (Environment Agency), and the geographic scope (England), and explicitly positions itself against less-authoritative approaches ("this is the feed the government broadcasts from, not a model"). It is immediately distinguishable from the sibling ukflood_areas and ukflood_station_readings tools.

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 clear trigger ("AUTHORITATIVE for 'is there a flood warning in <English place>'") and an explicit exclusion (England only; Wales/Scotland/NI publish elsewhere). It stops short of naming sibling tools (ukflood_areas, ukflood_stations_near) as alternatives, so routing between the flood tools is still partly inferred.

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