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

Annotations only say readOnlyHint=false and idempotentHint=false; the description adds the material behavior: no account or key required, the call returns immediately without blocking, the inbox is unowned until claimed, and it auto-expires in roughly two weeks regardless of use. These are exactly the facts an agent needs before committing to this lifecycle.

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?

The critical facts (no signup needed, returns immediately, not a confirmation by itself) are front-loaded, and every sentence carries workflow or lifecycle information. The ALL-CAPS emphasis and the slightly sprawling final sentence about claim_trial_inbox cost it a point on polish rather than substance.

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 zero-required-parameter tool with no output schema, the description covers return behavior ('Returns the inbox address IMMEDIATELY'), the follow-up call needed for the actual confirmation, and the expiry horizon. Nothing an agent needs to invoke it correctly is missing.

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?

There is one optional parameter (purpose_label) with 100% schema description coverage, so the schema already explains it and the baseline is 3. The description never references the label or what it affects in the returned inbox, so it adds no meaning beyond the schema.

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 concrete verb+resource ('Get a disposable email address (a temporary inbox)') and immediately scopes it ('NO Inbin account required', 'usable before the human has signed up'). It also explicitly demarcates itself from siblings by naming await_trial_inbox and claim_trial_inbox, so an agent can pick it without opening other schemas.

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?

Gives an explicit two-step workflow: call this, use the returned address to sign up, THEN call await_trial_inbox with the same address, plus an explicit warning that 'calling this alone does not get you a confirmation.' It also routes the permanent-address case to claim_trial_inbox, so both when-to-use and when-to-use-something-else are covered.

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