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

Annotations already cover readOnly, idempotent, openWorld and non-destructive traits, so the bar is lower. The description earns credit by disclosing the billing model (free daily allowance, then $0.002 USDC via x402) and the 7-day horizon, which are real behavioral facts absent from structured fields.

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 tight sentences with the core capability front-loaded and the pricing caveat second. No filler and no repetition.

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?

Output schema exists so return values needn't be explained, and annotations plus schema cover safety and parameters. The description adds the two things an agent can't get elsewhere: scope horizon and cost model.

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%, so the schema already documents days, datum, units, and station. The description restates the 7-day limit but adds nothing on datum or units of measurement, so the baseline 3 is appropriate.

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: predicted high/low tide times and heights, with a scope limit (up to 7 days from today). It distinguishes itself implicitly from tides__water-level via 'Predicted' vs observations, but never names a sibling, so it falls short of a 5.

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 and no alternatives named. An agent cannot tell from the text whether to use predictions, conditions, or water-level for a given question; only the word 'Predicted' hints at the future-facing case.

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