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

Annotations already establish read-only, idempotent, non-destructive behavior. The description adds the key behavioral trait that allowlists are per-leg and that omitting `ruleset` unions across legs while setting it scopes to one leg, which materially affects the result set.

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 short sentences, each carrying useful information: the action/scope, the relationship to the vault catalog, and the leg-filtering behavior. There is no filler or repetition of the schema.

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 two-parameter read-only list tool with an output schema, the description covers the only non-obvious behavior (ruleset omission) and the relationship to the broader catalog. An agent has enough to select and call it correctly without additional context.

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?

The schema already describes both parameters with 100% coverage, including the exact union-vs-scope behavior of `ruleset` and the Mongo `_id` nature of `campaignId`. The description's ruleset advice mirrors the schema rather than adding new parameter meaning, so the 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?

The description uses a specific verb ('List') and resource ('spells the campaign DM has added to the campaign's allowlists'), and positions it as a 'subset of the broader vault catalog,' distinguishing it from vault_search_spells and the add/remove campaign spell siblings. The title and name are reinforced rather than merely restated.

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 gives clear context for when to call this tool — when you need a campaign's DM-curated spell allowlists rather than the full vault catalog. It does not explicitly name an alternative or state when not to use it, but the scope and ruleset-union behavior make the usage context clear.

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