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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=true, so the safety profile is covered. The description adds the useful fact that no output schema exists by listing the returned fields (contact, address, time, device), but says nothing about pagination ordering, rate limits, or prerequisites such as the email having been sent.

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 short sentences, with the return contents front-loaded and no filler. The trailing REST path 'GET /Emails/{email_id}/Report/Opens' is largely redundant given the tool name and adds little for an agent, keeping it just short of 5.

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?

With no output schema, the field enumeration is genuinely helpful and is the main completeness contribution. However, for a report tool an agent may need to know the scope (single email id, sent campaigns only) and result ordering, neither of which is addressed; the description is adequate but not complete.

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 email_id, page, and page_size are already fully documented in the schema, including the 'pass the previous reply's next_page' note. The description contributes nothing parameter-related, so the baseline of 3 applies.

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 names a specific resource ('email opens') and enumerates the returned fields (contact, email address, time, device), which makes the purpose concrete. It does not explicitly differentiate itself from adjacent report siblings like benchmark_get_email_clicks or benchmark_get_email_bounces, but the 'opens' subject is unambiguous.

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?

There is no statement of when to use this tool versus benchmark_get_email_report, get_email_clicks, or get_email_bounces. Usage is only implied by the tool name, which leaves the agent to infer that this is the opens-specific slice of the report family.

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