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

Annotations already carry readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds real context beyond that: results are ordered by date with next spring/neap first, perigean spring tides are flagged, times are UK-local, and values are derived from lunar phases rather than harmonic predictions.

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 sentences, front-loaded with what is returned before the scope caveat. Every clause carries information: ordering, flagging, time zone, derivation, and the port-tide exclusion.

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 all three optional parameters are fully specified in the schema. For a simple read-only lookup, the description plus schema plus annotations leave nothing an agent needs 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 coverage is 100% and each of from/year/count has its default and range documented inline, so the schema does the heavy lifting. The description adds nothing parameter-specific (no interaction rules between from and year beyond what the schema states), which is the expected baseline 3.

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 and resource (returns dates of spring and neap tides derived from Moon phases) plus the ordering and flagging behavior. The closing sentence ('These are tide dates, not times or heights for a port') draws a sharp boundary against the common expectation of a port tide table, so an agent can tell exactly what it gets.

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 exclusion of port tide times/heights is a clear usage signal, and the domain (Moon phases, UK dates) is implied well enough to pick this over the moon-phase siblings. It never names an alternative tool or says when to prefer get_moon_calendar or find_moon_events, but no sibling computes tides, so the routing ambiguity is low.

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