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

The description discloses an important behavioral trait beyond the annotations: the operation depends on prior session state ('last generated or edited image') and returns a file path. This is meaningful context beyond readOnlyHint, openWorldHint, and destructiveHint. It does not, however, explain what happens if no prior image exists or whether the original file is replaced.

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?

Three short sentences with no filler. The description front-loads the core action, states the prerequisite, and ends with the return value. Every sentence earns its place.

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 two-parameter tool with full schema coverage and an output schema, the description provides the core behavior, the prerequisite, and the return artifact. It leaves minor edge conditions to inference, such as failure behavior when no prior image exists, but overall the agent has enough context to invoke the tool 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 description coverage is 100%, so the schema already documents the prompt and model parameters, including a prompt example and model enum values. The description adds little beyond calling the prompt 'a new prompt' and connecting it to the last generated/edited image. Baseline 3 is appropriate because the schema carries the parameter documentation burden.

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: 'Refine the last generated or edited image with a new prompt.' It clearly differentiates this from generate_image and edit_image by focusing on the existing last image rather than creating or editing from scratch. An agent can immediately understand the tool's role in the image workflow.

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 description gives an explicit prerequisite: 'Must call generate_image or edit_image first.' This makes the sequential usage context clear. It does not explicitly state when not to use this tool or contrast it with alternatives, but the prerequisite plus 'last generated or edited image' strongly implies the intended use case.

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