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

With no annotations supplied, the description carries the full behavioral burden and does so well: it discloses the cost ('Costs one image from the monthly image allowance' with exact per-plan quotas), plan gating, that the result is a draft the user must save, the library limit of 20, and hard content constraints on the look. That is unusually rich disclosure for a generation tool with zero annotation coverage.

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 main action is front-loaded in the first sentence and nearly every clause carries operational value (cost, plan, storage, restrictions). It is written as a dense run-on with semicolons and parentheticals, so it reads as a wall of text rather than a scannable structure, which costs it a point.

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 no-output-schema, no-annotation generation tool, the description covers cost, eligibility, storage/draft lifecycle, sibling relationships, and even the instruction to show the returned picture. It does not address failure modes, regeneration of a failed attempt, or latency, which are minor gaps given the otherwise thorough coverage.

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 already 100%, so the baseline is 3; the description adds real constraints beyond the schema, notably 'Keep looks to appearance and one outfit (for a child only hair, eyes, height and outfit)' and 'no held objects', which shape how the description parameter should be written. It also reinforces that photo_url must be a public https link rather than a chat paste, though that is largely duplicative of the schema.

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 and resource ('Create one character for a 3D Animated film as a Pixar-style 3D reference sheet, full body on white') and covers both input modes: written look or the user's own photo via photo_url. It also draws the boundary against a sibling by noting '3D characters are separate from the regular saved characters used by create_video,' so an agent can distinguish it from create_character and draw_character without opening a schema.

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?

Names the follow-on alternatives explicitly: 'the user can adjust it with change_3d_character' and 'manage_3d_character save keeps it in their 3D library (holds 20)'. It also states eligibility (Pro, Premium, Ultimate) and content exclusions (no held objects, no film or TV characters). It stops short of stating when to choose this over create_character/create_video characters directly, leaving that inference to the 'separate from' sentence.

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