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

Annotations already declare non-destructive, idempotent mutation behavior. The description adds genuinely non-structured context: the required auth scope and tier-based restrictions on what can be favorited. It does not restate annotation data, though it says nothing about return behavior (output schema covers that).

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?

Three compact sentences, with the core action front-loaded before the authorization and plan caveats. No filler or redundant restatement of the title.

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 simple one-parameter mutation with an output schema and full annotations, the description covers purpose, auth, and plan gating adequately. The only minor gap is that it doesn't mention behavior when the auction is already favorited, though idempotentHint already signals this.

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?

Only one parameter, and the schema documents it fully (100% coverage including the 10-character public-ID pattern). The description adds nothing about the `id` argument, so the baseline of 3 applies — the schema does all the work here.

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 combination ("Guarda una subasta en tus favoritos") in the very first sentence. The verb 'guardar' cleanly distinguishes it from siblings like favoritos_quitar and favoritos_listar without needing to name them.

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 concrete preconditions for use: an account is required with the `favoritos:write` scope, and plan limits determine which auctions can be saved (Radar/Starter active-only; `fav.historico` is Pro+). It doesn't explicitly route to an alternative tool, but the conditions of use are clear.

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