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

Annotations already disclose idempotentHint=true and destructiveHint=false; the description adds the upsert-like 'create or update' behavior and the fact that the character is reference-based. It does not disclose important operational constraints such as consent or rights gates, but those are documented in the schema properties, so the additional behavioral gap is moderate.

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?

One tight sentence that front-loads the operation, the resource kind, and the use case; no filler or restatement of the title. It earns its place, even though it sacrifices detail.

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?

Although an output schema exists, the tool has 14 parameters and a very low schema description coverage. The description leaves critical invocation questions open—how updates are keyed (characterId vs idempotencyKey), what reference assets are required, and which consent flags must be set. This is not complete enough for a complex write operation.

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 only 21%, so the description should compensate for the many undocumented parameters. It does not: no mention of idempotencyKey, characterId as the update selector, referenceAssetIds/primaryReferenceAssetId, voice fields, or storyFacts. The only hint is 'reference-based,' which weakly maps to the reference asset parameters.

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 ('Create or update') and resource ('reference-based character'), and adds the purpose context 'for repeatable faceless story generation.' This is enough to distinguish it from sibling read tools like characters_get/characters_list and from story-generation tools, even though it does not name a sibling explicitly.

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?

Provides a clear context by describing the intended use case—reusable characters for faceless story generation—but does not articulate exclusions or point to alternatives such as characters_list or generation_faceless_create. The agent can infer when to use it but is not explicitly steered away from sibling tools.

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