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

Annotations already provide readOnlyHint=true, idempotentHint=true, and destructiveHint=false. The description goes beyond by stating 'this tool never raises a protocol error — it returns {"error": ...}' and that 'Every call is read-only and idempotent, so after correcting the input it is always safe to retry.' No contradiction with annotations.

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?

Every sentence earns its place: core purpose, weighting principle, example, usage boundary, error behavior, safety note. Front-loaded with the most important information. No redundancy or fluff.

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?

Despite the tool's simplicity (2 params, simple logic), the description covers when to use, how parameters work via example, error handling, weighting strategy, and idempotent/read-only behavior. An output schema exists (signal true) and the description provides a sample output structure. An agent has everything needed to invoke the tool correctly.

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%—both parameters have descriptions. The description adds meaning by showing an example input mapping (minutes=50, segments list) and noting the weighting heuristic ('opener and closer get less time; core activities get more'). This clarifies how parameters affect results beyond the schema alone.

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 opens with 'Split a class period into timed segments with sensible weighting,' which clearly states the verb, resource, and outcome. A concrete example input and output reinforces the purpose. The sibling tools are unrelated (get_free_skill, grade_curve, etc.), so no sibling differentiation is needed.

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 says 'Use when one fixed class period must be divided into segments. Not for multi-day planning and not for spaced review, which the personal server's spaced_repetition_plan builds.' This gives clear when-to-use and when-not-to-use guidance, and names an alternative tool.

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