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

Annotations already declare readOnly, idempotent and closed-world, so the safety profile is covered. The description adds real behavioral context beyond that: no filter returns all 26 lessons, and it discloses the composition of the result (slug, título, descripción, nivel, forma de acceso, precio, resumen por nivel). It stops short of describing pagination or ordering, which is a minor gap for a fixed-size catalog.

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 core action and scope, then usage and routing in a compact sequence of clauses. The enumeration of returned fields is dense but earns its place by compensating for the absent output schema; the whole definition remains a single tight paragraph with no filler.

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 parameterless-filter, read-only list tool with no output schema, the description supplies everything an agent needs: scope, the shape of the returned records, the default behavior without filters, and the handoff to sibling tools. Nothing material is left to inference.

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% and the single enum parameter with its three values is fully documented in the schema, including the default behavior of returning all 26 lessons. The description corroborates the enum options but adds no format, syntax or edge-case detail beyond the schema, so the baseline of 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?

States a specific verb and resource ('Lista las lecciones del curso de MCP') and quantifies scope (26 lessons across three levels) plus the returned fields. It explicitly names the sibling tools it is not (buscar for a single topic, ver_leccion for a public sheet, leer_leccion for full text), so an agent can route 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 explicit when-to-use cases ('enseñar el plan de estudios completo o para obtener el slug de una lección') and an explicit when-not with the alternative ('para un tema concreto es mejor buscar'). It also names the downstream tools to call once a slug is obtained, which is exactly the selection guidance an agent needs.

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