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

Annotations only declare the generic mutation profile (readOnlyHint=false, idempotentHint=false, destructiveHint=false). The description adds real operational context beyond them: two distinct return links with different permissions, the constraint chain 2-100 distinct participant names, and euro-denominated amounts. It never warns that the non-idempotent create will spawn a duplicate group on a repeated call, which is the one behavior an agent would most benefit from knowing.

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?

Purpose is front-loaded and the sectioning (use cases, returns, limits) is easy to scan. However, the description is given twice, Spanish then English, roughly doubling its length with no added information for an agent that reads either language.

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 must carry the return contract, and it does: the group link (everyone can add expenses) and the admin link (required for anadir_gasto and ver_resultados). Combined with the participant and currency limits, an agent has what it needs to call the tool correctly, though duplicate-call behavior and post-creation workflow remain implicit.

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%, so the schema already documents titulo, participantes (2-100, distinct names) and the es/en idioma enum. The description's limits largely repeat the schema; only "importes en euros" adds information the schema does not encode. Baseline 3 is appropriate.

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 (creates a shared-expense group) plus its domain (trip, flat, dinner) and the core mechanic (who paid what, minimal-settlement calculation). It also names the downstream siblings (anadir_gasto, ver_resultados), so an agent can place it in the workflow without inspecting other 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?

Concrete invocation examples ("create an expense group for the trip with Ann, Luke and Mary", "split the holiday cottage costs between 6") make the intended context unmistakable, and it explains that the returned admin link feeds anadir_gasto and ver_resultados. It stops short of stating when NOT to use it versus siblings like crear_encuesta or crear_lista_quien_trae.

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