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

Annotations already declare readOnlyHint, idempotentHint and non-destructive, so the safety profile is covered. The description adds genuinely useful context beyond that: the required auth scope (message_read) and the two distinct 404 outcomes (inbox_not_found vs draft_not_found).

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?

Front-loads the trigger condition and returned fields, then auth and error semantics. Every sentence carries information, though the explicit 'Inputs: ...(required)' restatement is mild redundancy against the schema.

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?

No output schema exists, so the description compensates by naming the fields a caller can expect (labels, attachments, send_at, send_status, approval_status). With auth, error codes and return shape all covered for a simple 2-param read, nothing material 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 coverage is 100% and both parameters carry their own format hints (dft_…, inb_…/username/email), so the schema does the heavy lifting. The description adds only that both are required, which the schema already encodes via the required array.

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?

States a specific verb and resource ('get one draft') and enumerates the returned fields, which cleanly distinguishes it from cooper_list_drafts and cooper_get_message. An agent can select it without opening the schema.

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?

Explicitly says when to reach for it ('when you need one draft'), establishing the single-item vs list context. It does not name cooper_list_drafts as the alternative, so the routing is implied rather than spelled out.

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