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

Annotations already declare readOnlyHint=true, openWorldHint=false and destructiveHint=false, so safety is covered. The description adds meaningful domain behavior beyond that: consent requirements for real people, fictional characters taking no selfies, and which entry is the default. It does not describe the shape of the returned list, and with no output schema that gap remains.

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 scope statement is front-loaded and every clause carries information (consent, fictional flag, default, ambiguity rule). The nested parenthetical about selfies is dense and slightly awkward to parse, but no sentence is expendable.

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 list tool with no output schema, the description supplies the domain model needed to call it correctly and to interpret results. The only omission is what the returned entries look like and their ordering, which the agent must discover from the response itself.

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 tool takes zero parameters, so the baseline is 4. The description goes slightly beyond by explaining the implicit 'default character' state that callers of sibling tools rely on, even though there is nothing in the schema to disambiguate.

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 identifies the resource precisely — the user's characters — and defines the two kinds (selfie-based with consent, or invented fictional adults), which lets an agent distinguish the concept from list_photos or list_packs. The verb is implicit rather than stated (the title 'List characters' carries it), so it falls just short of a clean verb+resource statement.

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 explicitly states the default-resolution behavior and names the siblings that depend on it (start_shoot and add_selfie use the default when no character is passed). It also gives a concrete decision rule: when the user has more than one and hasn't specified, ask.

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