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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so safety is covered. The description adds valuable behavioral context beyond annotations: it mentions data lag (up to 6 minutes), the return format (UTC timestamps, water height in feet/meters, quality flags), the auth requirement (no auth, public domain), and the data source. This fully discloses operational behavior without contradiction.

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?

The description is concise (about 5 sentences) and front-loaded with the core action, followed by return details, usage instructions, alternative, and use cases. Every sentence contributes value—no fluff or redundancy. The structure flows logically from what it does to when to use it.

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?

Given the presence of an output schema and rich annotations, the description is complete. It covers the main purpose, return format, defaults, latency, alternative tool, use cases, and source. It does not need to detail every parameter since the schema does that. For an agent to decide and invoke correctly, nothing essential is missing.

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 baseline is 3. The description reinforces defaults (e.g., 'default: last 24 hours' for date range, 'Datum defaults to MLLW') and mentions units (feet/meters) but does not add meaning beyond what the schema already provides. It summarizes the parameter usage but does not introduce new semantics.

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?

The description states a specific action ('Get verified observed water level readings') with a precise resource (NOAA CO-OPS tide gauge station) and clearly differentiates from sibling coops.tides.predictions by noting it provides observed data and that predictions are for future forecasts. It also mentions the 6-minute interval and the distinction between observed vs. predicted, making the tool's scope 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?

The description explicitly instructs when to use this tool versus the alternative: 'Observed data may lag real-time by up to 6 minutes; use coops.tides.predictions for future forecasts.' It also lists concrete use cases (flood monitoring, storm surge analysis, historical tide research, comparing observed vs. predicted) and specifies the required station_id and optional date range with defaults. This is explicit, actionable guidance.

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