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

With no annotations, the description carries the burden and does disclose two non-obvious traits: cost behavior ('flat, no extra credits') and async behavior (returns a sheetJobId that must be polled). It does not say what happens if a sheet already exists, whether the operation is reversible, or what auth/entitlements are required.

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, front-loaded sentences with the primary action first and the workflow steps after; nothing is padded. The parenthetical about the retired sheet is slightly inside-baseball but earns its place by disambiguating against legacy tooling.

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 two-parameter, no-output-schema generation tool, the description covers what it produces, that it is async, how to poll, and what it costs. Remaining gaps (output contents, error cases, nsfw implications) are minor rather than blocking.

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 100%, so both parameters are already documented in the schema. The description only adds a pointer on where characterId comes from (ryla_list_characters) and says nothing about the nsfw flag's intent, so it adds marginal meaning over the schema — baseline 3 applies.

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 ('Build the 18-shot identity reference sheet for an existing character') and scopes it to existing characters, which cleanly separates it from the generate_base_image / generate_image siblings. The parenthetical pinning it as the live replacement for the retired character sheet removes ambiguity about which tool is current.

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?

Gives an explicit prerequisite path ('Use ryla_list_characters to find a characterId') and the follow-up step ('poll with ryla_generation_status'), so the agent knows the surrounding workflow. It stops short of naming when NOT to use it, e.g. how it differs in outcome from generate_base_image or generate_image.

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