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

The description explicitly states 'this overwrites the existing portrait image with the expression sheet', which is a destructive action on the existing image. This directly contradicts the annotation destructiveHint: false. The contradiction is severe and undermines the agent's ability to assess risk, warranting a score of 1. Other behavioral details (pure HTTP, unverified consistency) are provided but overshadowed by the contradiction.

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 front-loaded with the core purpose but then launches into a lengthy historical narrative with specific dates (2026-07-11, 2026-07-26) and technical details that are not directly relevant to invoking the tool. This reduces conciseness and may distract the agent from the essential operational details. The structure could be improved by moving historical context to a separate section or removing it.

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?

The description covers most operational aspects (how to specify expressions, which slot to write) but misses the entity_id parameter entirely, which is required. It also includes extraneous historical context that does not aid invocation. The description is not fully complete for an agent to call it correctly without guessing what entity_id refers to, and it lacks any mention of the output format, though no output schema exists. Overall, it is adequate but has clear gaps.

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?

With schema description coverage at 0%, the description must explain all parameters. It explains account (Google account that owns the project), expressions (list with default and recommended count), and character_slot_index (which slot, default 0, overwrites). However, it fails to explain the required parameter entity_id, leaving it undefined. This is a significant gap for a required parameter, so the description only partially compensates for the schema's lack of descriptions.

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 tool generates a single image of the character's face with multiple labeled expressions in a row, explicitly naming it an 'expression sheet'. It also distinguishes itself from the sibling generate_character_turnaround by noting same job type but different output, making the purpose 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 provides context on when to use this tool by referencing generate_character_turnaround and explaining the historical reason for its existence. It also offers usage guidance on the expressions parameter (keep to 3-5) and character_slot_index (0 overwrites portrait). However, it does not explicitly state when not to use this tool or compare it to other sibling image generation tools, leaving some inference.

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