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

With no annotations, the description carries the full burden. It discloses one behavioral trait ('deterministically'), but says nothing about whether this is a read-only lookup, what a returned lesson contains, or what happens when there is no next unit — significant gaps for a navigation tool.

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?

Front-loaded with the coach framing followed by the two key rules in a compact, well-structured pair of sentences. The '[WALK · door]' tag consumes space without evident value to an agent.

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?

For a simple 2-parameter read tool with no output schema and no annotations, the description adequately explains how to invoke it but omits the return shape and the end-of-sequence behavior. It is minimally viable but not complete.

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 0%, so the description must compensate, and it does explain both parameters: `after` as the preceding unit id (omit for the first) and `subject` as the path selector. It stops short of clarifying accepted `subject` format (id vs. name) or the meaning of the 4000-char limit.

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 resource and action: retrieving the next lesson/unit within a subject, with an explicit deterministic ordering. However, it does not distinguish itself from the many coach siblings (coach_unit, coach_subjects, coach_guidance), so an agent must infer the boundary.

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?

It gives clear calling conventions — omit `after` for the first unit, pass a unit id for the following one, and `subject` selects the path — which is useful usage guidance. But it never says when to prefer this over coach_unit or coach_subjects, so alternative selection is left to inference.

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