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

The description adds value beyond annotations by detailing error behavior: 'on invalid, missing, or malformed input this tool never raises a protocol error — it returns an error object' and reiterates the idempotent, read-only nature. This is fully consistent with annotations (readOnlyHint, idempotentHint, destructiveHint) with no contradictions.

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 front-loaded with purpose, followed by a clear example, usage guidelines, error handling, and safety note. Every sentence adds distinct value. It is appropriately sized for the tool's simplicity and well-structured for an agent to parse quickly.

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 tool's low complexity (2 parameters, output schema exists), the description covers all essential aspects: purpose, input format, algorithm, error handling, safety guarantees, and usage boundaries. The example of the output structure compensates for not needing to elaborate on the output schema.

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% with descriptions for both parameters. The description adds a concrete input example (minutes: 50, segments list) and explains the weighting logic ('opener and closer get less time; core activities get more'). This provides context beyond the schema's parameter descriptions.

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 'Split a class period into timed segments with sensible weighting', which is a specific verb and resource. It clearly distinguishes the tool from unrelated sibling tools like get_free_skill or readability_report. The example further reinforces the purpose.

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?

Explicit guidance is provided: '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 tells the agent exactly when and when not to use the tool, and names an alternative.

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