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

The description explicitly states what the tool does (marks as sent) and what it does not do (does not email), which is transparent. The annotations (readOnlyHint false) are consistent with a state-changing operation but provide minimal detail, so the description carries the burden adequately.

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?

The description is a single, concise sentence that contains no filler and directly conveys the essential information.

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 adequately covers the primary context of use and the key distinction (no email). It does not mention return values or errors, but given the simplicity of the operation and the lack of an output schema, this is not a significant omission.

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?

The schema has 0% parameter description coverage, and the tool description does not compensate by explaining that the 'id' parameter refers to the document ID. While the tool name and title imply this, the documentation leaves the parameter meaning implicit.

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 the specific verb 'mark' and identifies the resource 'document', clearly stating the action and its key nuance (without emailing). This distinguishes it from send_document which emails the document.

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 phrase 'without emailing it' provides a clear usage distinction from send_document, implying this tool should be used when the document needs to be flagged as sent but no email should be dispatched. However, it does not explicitly mention when to prefer it over other document-update tools like save_document.

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