Create character

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

With no annotations, the description carries the full behavioral burden. It usefully discloses that portrait generation consumes image credits and that the portrait is only generated when portrait_prompt is supplied — real value beyond structured fields. It does not cover permissions, name-uniqueness/collision behavior, or what identity/ID is returned for later update calls.

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 short sentences, front-loaded with the core action and the cost-bearing optional path. Every sentence carries information, though 'generates its look' slightly restates 'portrait'.

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 mutation tool with no annotations and no output schema, the description is adequate but leaves a gap: it doesn't indicate that the created character's id is needed for flow_update_character / flow_regenerate_portrait, nor describe failure modes. The cost disclosure partially offsets this.

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 coverage is 80%, so the schema already documents voice, project_id, personality, and portrait_prompt. The description reinforces that portrait_prompt drives image generation and that voice/personality feed the Flow agent, but adds little syntax or constraint detail beyond the schema descriptions. Baseline 3 is appropriate.

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?

States a specific verb+resource ('Create a reusable character') and even names the mechanism (Flow's character builder, Nano Banana). It does not explicitly distinguish itself from siblings like flow_update_character or flow_regenerate_portrait, but the verb 'create' plus 'reusable' makes the intent obvious.

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 implies usage through the conditional 'With portrait_prompt...' and the cost note about image credits, so an agent can infer that portrait generation is optional. However, it never says when to choose this over flow_update_character, or that flow_regenerate_portrait exists for updating an existing portrait.

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