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

The description adds significant behavioral nuance beyond the readOnly/idempotent/destructive annotations: monster-typed companions are excluded server-side, duplicate entries appear for multi-linked companions, each entry carries companionOf and a possibly-null primaryToken slice. This meaningfully informs the agent about results it would not otherwise expect.

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?

The description is dense but every sentence earns its place: purpose, read-only nature, management boundaries, server-side filtering, duplicate-entry semantics, result fields, and a useful pairing hint. Key information is front-loaded before deeper details.

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 one fully-documented parameter, rich annotations, and an output schema, the description still adds critical context: exclusion behavior, duplicate handling, field semantics, and the companionOf relationship. An agent has everything needed to select and 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% and the single parameter campaignId is fully documented as the Mongo _id of the campaign. The description adds no extra parameter-specific detail, but none is needed given the schema already covers it.

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 names a specific verb and resource: listing companions attached to a play campaign's characters, and clarifies they are the 'supporting cast' beyond the roster. This clearly differentiates it from sibling tools like play_list_campaign_characters and play_list_campaign_players.

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: it is read-only, the companion tie is managed elsewhere via vault_attach_companion/vault_detach_companion, and it suggests pairing with vault_get_character for full sheet details. It does not explicitly spell out when not to use it relative to play_list_campaign_characters, but the intent is clear.

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