Replace an image

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

Annotations already carry the readOnly/destructive/idempotent flags, so the bar is lower. The description adds genuine context beyond them: it specifies what is preserved (frame, position, effects), what effect each replace_method has on the bitmap (center_inside scales to fit keeping aspect; center_crop fills and crops overflow), and that upload/cleanup behavior matches create_image. This meaningfully clarifies what the destructiveHint implies.

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 sentences with no filler: the first states the core action and preserved attributes, the second bounds the input sources with a cross-reference, and the third defines the enum semantics. The most decision-relevant information (what is swapped, what is kept) is front-loaded.

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 5-parameter mutation tool with no output schema, the description covers the core behavior, preserved properties, input-source constraints, and method semantics. The only gap is that it doesn't describe the response shape or error conditions, but since the operation is a straightforward bitmap swap and the schema documents required params, this is a minor omission rather than a blocking one.

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 the baseline is 3. The description adds value beyond the schema by explaining the behavioral difference between the two replace_method enum values (scale-to-fit vs. crop-overflow) and by clarifying that image_url/image_path inherit exactly the same validation, upload and cleanup rules as create_image, which the schema's 'exactly one of' constraint alone does not convey.

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 opens with a specific verb ('Swaps') and resource ('bitmap of an existing image element') and names the underlying API (batchUpdate replaceImage). It also distinguishes itself from create_image by stating it preserves frame, position and effects, which is exactly what separates this sibling from create_image in the sibling list.

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 first sentence implies the use case: replace an existing image while keeping its frame/position/effects, and the cross-reference to create_image's validation/upload/cleanup rules gives the agent a known behavioral contract. However, it never explicitly states when not to use this tool or names an alternative approach (e.g., delete_object + create_image), so it lacks the explicit exclusions needed for a 5.

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