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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered; the description adds the non-obvious behavioral fact that coverage depends on module-level change-tracking support, with a concrete confirmed/not-confirmed module list. It stops short of describing volume or pagination characteristics of the diff, which keeps it off a 5.

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 core statement is front-loaded in the first clause, and the trailing parenthetical carries genuinely load-bearing coverage caveats rather than filler. The nested aside is somewhat dense but every clause earns its place.

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-value explanation is unnecessary, and annotations plus the 100%-covered schema handle safety and parameters. The one thing an agent could not infer — silent coverage gaps for custom modules — is exactly what the description discloses.

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 the schema already specifies the Unix timestamp semantics of 'since' and the PLATO/Moodle numeric id for 'course_id'. The description adds only 'since a given time', so the baseline 3 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?

The description opens with a specific verb and resource ('Get what changed in a course since a given time') and then enumerates the domains covered (configuration, completion, grades, submissions). It explicitly distinguishes itself from the contents/notice-listing siblings, so an agent can tell it apart without inspecting schemas.

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 names the exact condition under which this tool under-reports ('this won't catch a new ubfile lecture or ubboard post') and routes the agent to named alternatives ('use get_course_contents/list_notices instead'). That is explicit when-not plus alternative routing, not implied guidance.

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