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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the description only needs to add context beyond those. It does this by specifying the caller-scoped nature of the results and the DM-or-player coverage. Mentioning the returned id also implies the output contains character ids usable by vault_get_character, which is helpful.

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?

Two crisp sentences with no filler. The primary action is stated first, and the alternative tool reference is placed second. Every sentence earns its place.

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 zero-parameter, read-only list tool with an output schema and safety annotations, the description is complete. It tells the agent what results are returned, who they belong to, and how to follow up for full character details.

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 input schema has zero parameters, and schema description coverage is 100%, so parameter semantics are trivially satisfied. The baseline of 4 for no-parameter tools applies; the description does not need to add parameter details.

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 clearly states the verb and resource: 'List the characters the calling user has in any of their campaigns (DM or player).' It also distinguishes itself from related tools like vault_get_character by noting that full sheet data belongs there. The scope is explicit and unambiguous.

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 for when to use this tool versus vault_get_character: for a quick list of a user's characters across campaigns, and for full sheet data use vault_get_character with the returned id. It does not explicitly mention play_list_campaign_characters as an alternative for per-campaign listing, but it provides enough routing guidance to be useful.

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