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

Annotations cover the safety profile (readOnlyHint=false, destructiveHint=false, non-idempotent, open-world), so the description doesn't need to restate them. It adds real value beyond that: the image is "stored permanently", the voice clip is "trimmed to 10 seconds", the returned handle "cannot be changed later", and the result is private until published in the app. Missing are failure behaviors (bad image URL, name/handle collision) and whether a duplicate name is allowed.

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 sentences, front-loaded with the core action, followed by the return-value/mention tip and the publishing exclusion. Every clause earns its place and nothing is padded.

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 no output schema, the description correctly compensates by explaining that the tool returns a `handle` and how to use it downstream. For a 5-parameter mutation tool with full annotation and schema coverage, the main remaining gap is error and uniqueness behavior. Otherwise it is complete enough to invoke correctly.

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 parameter documentation is already handled by the schema. The description restates the accepted image forms (https URL or data URL of JPEG/PNG) and the voice trimming, but actually omits the "upload URL" option the schema lists, and adds no format detail the schema lacks. Baseline 3 is correct here.

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 ("Save a private character from a name and an image") and immediately scopes it against the sibling actions: private creation here, publishing "in the Mage app", deletion elsewhere. An agent can tell this apart from delete_character or list_characters 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?

It gives a usable boundary: this creates a *private* character, and publishing is explicitly out of scope ("Publishing a character happens in the Mage app"). It also tells the agent the post-condition needed to proceed ("mention it in a generate prompt as @handle"), implying the create-then-generate flow. It stops short of naming sibling tools like list_characters or delete_character as alternatives.

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