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

Beyond the annotations, it discloses an important behavioral trait: the attachment is not immediately usable, but only once its ID is in READY state. It also implies a non-read, stateful operation, consistent with readOnlyHint=false. This readiness behavior is not available from annotations or schema alone.

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 carry all essential information: the verb, the resource, the source categories, and the readiness condition. It is front-loaded with purpose and contains no filler or redundant restatement 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 tool with a rich nested input schema and an output schema, the description covers what an agent must know outside the schema: the types of sources accepted and the need to wait for READY before using the returned attachmentId. No critical operational guidance is missing.

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 fully documents all parameters and nested source variants. The description only summarizes the three source categories already defined as the oneOf variants, adding no new meaning beyond 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 clearly states a specific verb ('Prepare') and resource ('an attachment'), and enumerates the three supported source types: client upload, existing mail attachment, or original .eml. This differentiates it from siblings like read_attachment and send_email by naming the exact input forms.

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 context for when to use the tool: when an attachment must be prepared from one of the listed sources. It also adds a key usage condition, 'Use its attachmentId only when READY,' though it does not explicitly contrast with alternative tools.

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