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

With no annotations, the description carries the full burden and does well: it discloses that no signup is required, that a read_token is returned once and must be saved (a real irreversibility warning), and that expiry depends on free vs. paid tier. It omits rate limits, idempotency, and what the Ed25519 identity is for, so it is not exhaustive.

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 tight sentences, front-loaded with the purpose, then the critical 'save the read_token' warning, then the paid upgrade path. The 'No signup.' fragment earns its place as a key behavioral fact.

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?

Although no output schema exists, the description enumerates the return payload (address, read_token, expiry, Ed25519 identity), which is exactly what an agent needs to consume the result. All four optional parameters are covered by the schema, so nothing material 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?

Schema description coverage is 100%, so the schema already documents alias, purpose, ttl_hours, and account_key in detail. The description only restates the account_key/credits behavior, adding no syntax or constraint detail beyond what the schema provides.

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 email inbox') plus the concrete use case (receive verification codes and magic links), so an agent immediately understands the tool. It does not name a sibling or explicitly contrast itself with alternatives like create_account or create_deposit, keeping it just below a 5.

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?

Implies when to use it through the 'AI agent receiving verification codes and magic links' framing, and gives an explicit conditional ('Pass account_key to buy a longer-lived inbox with credits'). No exclusions or explicit 'use X instead' routing to siblings is provided.

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