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

Annotations only supply the generic mutation profile (not read-only, not idempotent, not destructive, closed-world). The description goes well beyond them by disclosing the leg-matching mechanic, the active-leg prerequisite, and the concrete authorization requirements (owner/accepted GM or player seat, owner or Admin Mode).

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 tight sentences: purpose and mechanic first, then preconditions and auth, then the lookup hint. No filler, no repetition of schema fields, and every sentence carries information an agent would otherwise have to guess.

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 mutating, permission-gated tool, the description covers the action, its placement rule, the prerequisite state, and the authorization model; an output schema exists so return values need not be described. Nothing material is missing for correct invocation.

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 campaignId, characterId, and the npc flag; baseline is therefore 3. The description adds only the sourcing hint for characterId and omits any discussion of the npc parameter's DM-controlled semantics, so it adds marginal value only.

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 ('Attach a vault character to a play campaign') and immediately explains the effect: the character participates in play and the attachment lands on the campaign leg matching the character's ruleset. This is precise enough to distinguish it from sibling attachment tools like play_add_campaign_item or vault_attach_companion.

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 clear preconditions - the campaign must have an active leg for the character's ruleset, the caller must hold a seat, and must be able to edit the character - plus a routing hint to vault_search_characters for the id. It does not name explicit alternatives or a when-not-to-use case, so it stops short of a 5.

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