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

Annotations already declare readOnlyHint, but the description adds substantial behavior: characters are scoped to 'YOU created', the response is ordered oldest first, source values are semantically defined, and the critical caveat that portrait_media_id null means no usable reference yet. This goes far beyond the annotation hints.

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 compact and front-loaded: the core action and scope appear in the first sentence, followed by the read-only benefit, return shape, and field semantics. Every sentence adds operational value with no filler.

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?

Although there is no output schema, the description fully documents the return object, field names, ordering, source semantics, and the null-reference caveat. With zero parameters and read-only annotations, nothing essential is missing for an agent to call 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?

The tool has zero parameters and the schema is empty, so the baseline is 4. The description does not need to explain any parameter details, and it compensates by precisely explaining the output fields that matter, especially portrait_media_id.

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 uses a specific verb and resource: 'List the characters YOU created', and immediately distinguishes this from creation tools by naming create_character_from_description and create_character_from_photo. It also explains how the result connects to generate_with_face, making the tool's role in the workflow unmistakable.

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 clearly communicates when to use this tool: when you need to see your existing characters or find a reference for generate_with_face. It also states read-only behavior and that no credits are spent, but it does not explicitly list alternative tools to choose instead under certain conditions.

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