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 endpoint path and the metric set, which is useful, but it says nothing about auth requirements, latency, or whether metrics are computed live vs. cached. With annotations carrying the safety burden, a 3 is appropriate.

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 compact sentences: the outcome and metric list come first, the endpoint path last. Every token earns its place and nothing is padded.

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 simple read-only, single-parameter tool with no output schema, the metric enumeration effectively previews the response shape, so the agent knows what it will get back. The mild gap is that it doesn't clarify behavior for ids belonging to drafts or unsent emails, but for a read it is nearly 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% and the single parameter email_id is fully documented in the schema, including its prefixed-id format. The description adds only the implicit constraint that the id must refer to a sent email, which is marginal. Baseline 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?

States a specific verb+resource ('Delivery and engagement numbers for one sent email') and enumerates the exact metrics returned, which distinguishes it from buttondown_get_email (metadata) and buttondown_get_automation_analytics (automation-scoped). 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?

The phrase 'for one sent email' implies the usage scope versus aggregate/sibling analytics tools, but there is no explicit when-to-use guidance, no statement that the email must already be sent, and no named alternative. Usage must be inferred.

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