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

Annotations already declare readOnly, idempotent, non-destructive and open-world, so the safety profile is covered. The description adds genuinely new behavioral information not present in annotations: that API keys and SMTP credentials are never returned, telling the agent what field-level data is redacted. It lacks any note on result size or pagination behavior, keeping it below a 5.

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?

A single compact sentence with no filler, front-loading the read mode and the returned resource. The parenthetical auth note is slightly cryptic but costs little space.

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 read-only, zero-required-parameter list tool with rich annotations and no output schema, this covers purpose, auth mode, and the key data-safety caveat. The remaining gap is search semantics and paging behavior, which an agent could infer from field names.

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?

With 67% schema coverage, limit and offset are documented in-schema and the description adds nothing about them. The `search` parameter has no description in either place, so the description does not compensate for the one real gap; baseline 3 is appropriate.

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 ("List sub-accounts") plus the scope of returned data ("safe account metadata"), which is clear enough to distinguish it from the singular sendpost_get_subaccount sibling. It stops short of naming that sibling or the stats-listing siblings explicitly.

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 "READ (account key)" prefix hints at the auth mode and read nature, but there is no statement of when to use this tool versus sendpost_get_subaccount or sendpost_list_subaccount_stats. No pagination or filtering guidance beyond what the schema already implies.

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