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

No annotations are supplied, so the description carries the full burden. It makes clear this is a pure, stateless geometric computation with no side effects, and it discloses the conventions of the result (side of track reported as port/starboard, plus along-track distances). It stops short of stating units or input validation behavior such as what happens with degenerate waypoints.

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, front-loaded sentence that defines the metric before listing outputs. It is tight, though the trailing clause about port/starboard and along-track distances restates material that the output schema already covers.

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?

With an output schema present, return values need not be explained, and all three required parameters are fully documented in the schema. The only gap is the absence of guidance linking it to the related bearing/distance tools, which is minor for a self-describing calculation.

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% and each lat/lng field documents accepted formats (signed decimal, hemisphere letter, DDM, DMS) in detail. The description adds only the semantic mapping of the three points (two waypoints plus vessel position), so the schema does the heavy lifting and a 3 baseline applies.

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 (calculate) and a precisely defined resource (cross track error), then spells out the geometry: perpendicular distance from a position to the great-circle track between two waypoints. This is unambiguous and clearly distinct from siblings like calculate_distance or calculate_bearing.

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 definition of XTE implicitly tells an agent when the tool applies, but it never explicitly states when to prefer it over calculate_distance or calculate_bearing, nor any preconditions. Usage is inferable rather than stated.

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