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

Annotations already declare readOnlyHint=true and openWorldHint=true, so safety is covered. The description adds value beyond that by disclosing the row shape (member email + timestamp) and the pagination model ('use next_start'), which is exactly the context needed to consume results.

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-loaded with the core purpose, then comma-separated kind list, then output and paging notes. Every sentence earns its place with no filler.

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 description carries return-value information and does so adequately (row contents, paging). Minor gaps remain around kind-specific filters and whether mailing_id errors are surfaced, but an agent has enough to call it correctly.

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%, so baseline is 3, but the description adds semantic meaning to enum values ('in_progress = still in the queue', 'deliveries = delivered or bounced') that raw enum labels don't convey. It does not add detail on link_id/member_id/delivery_type filters, which remain schema-only.

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 ('Who did what with one mailing') and enumerates the activity kinds, so the agent knows exactly what is listed. It doesn't explicitly name siblings like emma_list_mailing_links or emma_get_mailing_response, but the per-mailing activity scope is clear.

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 mapping of kind values to activity types implies how to use the tool, but there is no explicit when-to-use or when-not-to-use guidance versus alternatives such as emma_get_mailing_response (aggregate) or emma_list_mailing_links.

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