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

Annotations already declare readOnlyHint=true, so the read-only behavior is covered. The description adds useful context: only one image is returned, only from completed jobs, and the operation is free. It does not describe error behavior for invalid job IDs or out-of-range indices, but the schema and annotations cover much of the safety profile.

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 short sentence contains the operation, the object, the condition (completed), and the return type (image content), with '[free]' appended. There is no filler or repetition of schema fields.

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 simple two-parameter read-only tool with full schema coverage and no output schema, the description is nearly complete: it identifies the return content and the required job state. It could be more explicit about using image_batch_status first, but this is a minor gap.

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%, with job_id and index already documented including zero-based indexing and the 0-49 range. The description adds no parameter-level information beyond saying 'specified one image', so it stays at the schema-covered baseline.

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?

The description uses a specific verb and resource: it returns one specified image from a completed batch job as image content. It does not explicitly name sibling tools, but the contrast with image_batch_create and image_batch_status is clear from the wording (completed result vs creating/status).

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 word 'completed' implies the tool should be used after a batch job finishes, and the 'result' phrasing distinguishes it from status-checking or creation. However, it does not explicitly state when-not-to-use it or point to image_batch_status as a prerequisite/alternative.

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