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

Annotations already cover read-only, idempotent, open-world and non-destructive semantics, so the bar is lower. The description adds genuinely new behavioral context: a free daily allowance followed by $0.002 USDC per call via x402, plus the fact that the payload includes the latest reading. It does not mention rate limits, latency, or data freshness beyond that.

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?

A single dense sentence that front-loads the resource and resolution before the pricing detail. No filler, though the pricing clause in the same sentence slightly crowds the core capability.

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 values need no explanation, and annotations carry the safety profile. Cost and the hour window are covered; what remains thin is any hint about data recency/latency or how station ids should be sourced, which siblings like tides__search would supply.

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 all four parameters and their defaults, making 3 the baseline. The description adds one fact not in the schema — the max of 72 hours — but nothing about datum choices, units, or station id format.

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+resource: 'Observed 6-minute water levels' with the resolution and the inclusion of the latest reading. The word 'Observed' implicitly separates it from the sibling tides__predictions, but no sibling is named explicitly.

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 when-to-use guidance relative to tides__predictions, tides__conditions, or tides__station. The only contextual statement is a pricing/allowance note, which tells the agent about cost, not about tool selection.

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