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

Annotations only cover the safety profile (readOnly=false, destructive=false, idempotent=false), so credit goes to the description for disclosing that the call provisions a new real address, returns address/expiresAt/secret, and that the secret is required to read the mailbox later. The free-tier 60-minute vs. paid 1440-minute distinction and OTP extraction are genuinely extra context. It stops short of saying what happens on expiry or whether mailbox creation is rate-limited.

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?

Three dense sentences, front-loaded with the core action and the returned fields, then tier limits. No filler, though the parenthetical tier clause is slightly compressed and could read as one run-on.

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 the return-value burden and does so — it names every returned field and explains the secret's role. Combined with the tier limits on ttlMinutes, an agent has everything needed to invoke and then consume the result.

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% and the single ttlMinutes parameter is fully documented (default 15, cap 60 free). The description reinforces the tier caps but adds no syntax or behavioral detail beyond what the schema already says, so the baseline of 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 and resource ('Create a disposable receivemail.dev email address that receives real mail') with the key property that makes it useful — real inbound mail delivery. The action is unambiguous and clearly distinct from the sibling read/wait tools list_messages and wait_for_email.

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?

Usage is implied by the resource (spin up a throwaway inbox, then read with the secret), and the free-vs-paid tier notes help an agent reason about the ttlMinutes choice. However, there is no explicit 'use this when…' framing, no mention of when not to use it, and no routing advice relative to the siblings.

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