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

With no annotations, the description carries the full burden and delivers: rate limits (20/hour, 100/day per mailbox), a hard precondition on mailbox configuration, an irreversible-write warning framed as prompt-injection defense, and a plain-text-only constraint. It omits what happens when limits are hit and any error/return behavior, which keeps it short of 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?

The core action is front-loaded in the first clause, and each following sentence adds a distinct constraint (precondition, safety, limits). It is dense with em-dashes and embedded clauses, so slightly heavy, but no sentence is filler.

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 mutation tool with no annotations and no output schema, the description covers preconditions, safety guardrails and throughput limits, which is what an agent needs to invoke it responsibly. Return handling and failure modes are left unspecified, but the essentials are present.

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 baseline is 3. The description only reinforces reply semantics already documented for reply_to_uid and body; it adds no format or default details 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 ('Send an e-mail right away') and immediately distinguishes the two modes: a new message vs. a reply via reply_to_uid. It also names the sibling it is not (mail_draft), so an agent can route correctly without opening either schema.

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 alternative and the condition that selects it: use mail_draft unless the mailbox owner has enabled 'the agent may send without my approval'. It adds a second guardrail about only sending what the owner asked for. Nothing is left to inference.

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