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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, covering the safety profile. The description adds valuable behavioral context: it lists the exact return fields and the recommended call ordering. It does not repeat annotation data, and adds the 'call first' directive which is a useful behavioral trait beyond annotations.

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 sentences with zero redundancy. The return list is front-loaded, and the critical usage instruction ('Call this FIRST') follows immediately. Every word earns its place.

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 enumerates the return fields, providing all necessary information about what the caller will receive. It also gives the usage context (call first) and requires no additional parameters. For a zero-parameter, read-only tool, this is 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?

The tool has zero parameters, so the schema trivially covers 100% of them. The description does not need to add parameter details because there are none. Per the baseline for 0-parameter tools, a score of 4 is appropriate; no additional parameter information is required.

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 states a specific verb ('Returns'), the resource (workspace), and enumerates the contents (scopes, plan, remaining emails, sending domains, senders). It clearly distinguishes itself from sibling tools like get_email or list_campaigns, which operate on different resources.

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 instructs 'Call this FIRST' and explains why: it tells which address to send from before attempting anything. This gives clear when-to-use guidance and implicitly positions it as a prerequisite for email operations.

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