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

Annotations already declare destructiveHint=true and idempotentHint=true, so the description's job is to add specifics, which it partly does: 'Fields left out stay' discloses merge-not-replace semantics and 'The forwarding key comes back once, as forward_secret' discloses a one-time secret return that no output schema documents. It doesn't spell out what is actually destroyed (e.g. rotating invalidates the old key, null turns off forwarding), which is a gap given destructiveHint=true.

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?

Front-loads the verb and resource, then packs the field list and the two behavioral notes into a tight, semicolon-delimited sentence set with no filler. Minor cost: 'same address' for inbox_instance_id is opaque and briefly slows the reader.

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 7-parameter mutation tool with nested objects and no output schema, the description covers what can be set, that omitted fields persist, and the one returned value an agent must capture (forward_secret). Annotations carry the safety profile, so the remaining omissions (auth fallback, rotation consequences) are secondary.

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% and the nested verify/forward/handshakes properties are documented in detail in the schema itself, so the schema already does the heavy lifting. The description restates the same shapes at a glance (preset list, {url} or null) but adds no semantics beyond it; baseline 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 ('Set') and resource ('your webhook inbox pro plan') and enumerates exactly which fields are configurable: forwarding, signature verification and handshakes. The 'Set' framing plainly contrasts with the read-side sibling inbox_pro_get, so an agent can pick between them 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?

Usage is implied by the field list: call this to configure forwarding, verification or handshakes, and 'Fields left out stay' signals partial-update semantics. But nothing states when NOT to use it, when to pair it with inbox_pro_get, or when rotate_forward_secret/passport_token matter, so the agent must infer routing.

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