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

Annotations already declare readOnlyHint=false, openWorldHint=true, idempotentHint=false and destructiveHint=false, so the mutation profile is known. The description adds genuinely useful context beyond that: a plan/entitlement prerequisite and a constraint that the image must be a public PNG or JPEG URL. It does not explain failure behavior or whether repeated calls create duplicates, so it is additive but not rich.

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?

Two short sentences with the action and its input format front-loaded, followed by the prerequisite. Nothing is wasted and no sentence repeats the schema verbatim.

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?

With three required, fully documented parameters and an output schema present, the description covers what an agent needs to call the tool correctly. The one gap is that "consistent character" is never unpacked — it is unclear whether the character is reusable across episodes or projects, which matters for planning a call sequence.

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 description coverage is 100%, so baseline is 3; the description slightly exceeds that by restating the imageUrl format constraint at the top level. However it adds no meaning for name or description beyond what the schema already documents.

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 a new consistent character") plus the accepted input format (PNG or JPEG image URL), so the agent knows exactly what the tool produces. It does not name sibling tools such as list_characters or delete_character to distinguish itself, so it stops short of a 5.

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 only usage guidance is the prerequisite "Requires an active Revid plan," which tells the agent about an account condition but not when to pick this tool over siblings or what the character is used for downstream (e.g. episodes). Usage is implied rather than spelled out.

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