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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so safety is covered. The description adds a genuinely useful behavioral fact the annotations cannot convey: the pricing model (free within a daily allowance, then $0.001 USDC per call via x402). It does not discuss rate-limit ceilings or result freshness, but the cost disclosure is meaningful added 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?

Two short sentences with zero waste. The scope statement is front-loaded ahead of the commercial detail, so the agent gets the 'what' first and the 'cost' second.

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?

An output schema exists, so return fields need not be explained, and the cost model is disclosed. The description stops short of noting coverage limits (England only, tidal gauges only) as an explicit exclusion, but for a zero-parameter listing tool this is close to complete.

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?

The tool takes zero parameters, so there is no parameter surface for the description to explain. Baseline of 4 applies; nothing is misleading or missing.

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?

Names a specific resource ('tidal level monitoring station') and bounds it geographically ('in England'), which implicitly separates it from the river-station siblings. It reads as a noun phrase rather than stating the verb (list/retrieve), but the operation is unambiguous.

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?

No guidance on when to pick this over sibling tools such as uk-flood__river-stations, uk-flood__stations-near, or uk-flood__station. The agent must infer from the phrase 'tidal level' alone that this is the tidal-station listing.

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