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

Annotations already declare readOnlyHint, idempotentHint, and closed-world, so the safety profile is covered. The description adds a genuinely new behavioral fact not present in structured data: it requires an authenticated session ("Necesita iniciar sesión"). It stops short of describing pagination or failure behavior, but for a small read-only tool this is solid.

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: the return contents come first, then the auth requirement, then the usage rule and follow-up. Information-dense and free of filler, though the opening sentence packs a long list of fields that could be slightly tighter.

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 no output schema, the description carries the return-value burden and does so by naming the exact fields returned, plus the auth requirement and the routing to leer_leccion. Nothing an agent needs to invoke it correctly is missing.

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?

Zero parameters, so the baseline is 4. The description confirms this explicitly ("No tiene parámetros"), which is consistent with the empty schema and leaves nothing ambiguous for the caller.

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+resource (student's progress in the course) and enumerates exactly what is returned: completed lessons by level, percentage, last five finished, and the next one with its URL. This clearly separates it from siblings like leer_leccion, ver_leccion, and mi_cuenta without opening any schema.

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?

Gives an explicit trigger ("when the person asks where they are or what to study now") and names the follow-up tool and action (open the next lesson with leer_leccion). The agent knows both when to call this and what to do next.

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