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

The description adds substantial behavioral context beyond the annotations: it replaces the existing cover, performs upload and attach in one step, restricts formats to PNG/JPEG, and explains that omitting `crop` shows the whole image. The annotations only indicate non-read-only, non-idempotent behavior, so this is meaningful addition.

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?

Four sentences, front-loaded with the core action, then constraints, then the removal alternative. Every sentence earns its place; no filler or repetition of schema details.

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?

The description is complete enough for correct invocation: purpose, parameter choices, format restrictions, crop semantics, and removal path are all covered. It does not describe the return value, and there is no output schema, but this is a minor gap for an action-oriented tool.

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 schema already documents all four parameters. The description adds value by reinforcing the either/or relationship between `source_url` and `image_base64` and by explaining the default behavior when `crop` is omitted, which is absent from the schema.

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 states a specific verb and resource: 'Replace a collection's cover image: uploads the image and attaches it in one step.' It makes the tool's scope unmistakable and, with the title and sibling names, the resource (collection vs. link vs. page image) is clearly distinguished.

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 clear usage conditions: supply either `source_url` or `image_base64`, PNG/JPEG only, and `crop` optional. It also provides an explicit when-not and alternative: 'To remove an image, call split_update_collection with image_upload_id: null.'

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