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

Annotations only give the generic readOnly=false / openWorld=true / destructive=false profile; the description adds the material substance: this is an upsert that overwrites an existing character of the same name, a 5-character cap, a legal/consent gate via rights_confirmed, and a refusal policy. It also explains that a failed test render names the missed traits, turning a possible failure into actionable guidance.

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?

Front-loaded with the core action and scope, then constraints, then returns — a logical order with no filler sentences. It is denser than strictly necessary (three paragraphs for a 5-parameter tool), which keeps it just below top marks.

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?

There is no output schema, and the description compensates with a dedicated RETURNS section covering the stored character, traits/marks/style, test-render pass/fail semantics, the sheet_view_url (with its one-hour expiry), and the updated character name list. An agent has everything needed to call it and interpret the result.

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 the baseline is 3; the description still earns above it by explaining what happens to image_urls (cut out onto one reference sheet, traits read off, one test render judged) and why rights_confirmed must be true. It adds no detail about 'domain' beyond the schema, keeping it from a 5.

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 ('Register a character the brand owns') and clarifies the scope with concrete examples (mascot, team member, recurring persona). It also discloses upsert behavior ('or replace the one of that name'), which distinguishes it from remove_brand_character and from the creative-generation siblings like generate_brand_creative.

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 precondition ('Before calling, confirm with the user...') plus a hard quota ('A brand keeps at most 5 characters') and a refusal policy for public figures and hateful content. It does not name sibling alternatives (e.g., remove_brand_character or generate_brand_creative) for related tasks, so it falls short of a 5.

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