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

The description discloses a non-obvious behavior: the attachment is placed on the campaign leg matching the vault character's ruleset, not chosen by the caller. It also adds a permission requirement ('contribute') that annotations do not capture. Since the annotations are all false flags, this behavioral detail is especially valuable, though duplicate-attachment behavior is not addressed.

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, purposeful sentences: action, behavioral constraint, then permission and workflow. Every sentence carries new information and the most important content is front-loaded.

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?

Given an output schema and a simple 3-parameter input, the description covers the prerequisite active leg, the ruleset-matching behavior, the permission requirement, and the pre-step for locating the character id. An agent has everything needed to invoke this tool correctly.

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 baseline is 3; campaignId, characterId, and npc are already documented in the schema. The description adds workflow context for characterId by referring to a 'vault character' and its ruleset, but it doesn't need to restate parameter definitions.

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 opens with a specific verb-resource pair ('Attach a vault character to a play campaign') and states the purpose ('so the character participates in play'). It clearly differentiates this from read/list tools like play_list_campaign_characters and from vault_attach_companion by focusing on play campaign participation.

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?

The description gives clear context: the campaign must have an active leg matching the character's ruleset, and the caller needs 'contribute' permission. It also instructs the agent to use vault_search_characters first to locate the character id. It doesn't explicitly state when-not-to-use, but no natural alternative tool exists for this exact operation.

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