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

Annotations already declare destructiveHint=true, idempotentHint=false and readOnlyHint=false, so the safety profile is covered. The description adds two facts not in structured data: the new secret is returned only once, and the old secret continues signing for the grace period — both operationally critical for a rotation. It does not spell out that expire_previous_in=0 kills the old secret immediately, nor any rate-limit/permission requirements.

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?

Two sentences, no filler; the core action and the one-shot return are front-loaded before the grace-period nuance. Every clause carries information an agent needs.

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 usefully signals that the new secret comes back in the response exactly once, which is the main thing an agent must handle. It leaves the response shape and the meaning of expire_previous_in=0 to inference, a minor gap for a two-parameter mutation.

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 both properties carry descriptions, so the schema does the heavy lifting. The description's note that expire_previous_in 'keeps the old one signing for that many seconds' largely restates the schema text, adding no unit/range detail the agent could not already read.

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?

"Replace a webhook endpoint's signing secret" is a specific verb plus a specific resource, immediately distinguishable from update_webhook, create_webhook and test_webhook in the sibling list. It stops short of naming or excluding those alternatives explicitly, so it is clear but not sibling-routing.

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?

The second sentence supplies the operative scenario: use expire_previous_in so a receiver can switch secrets without dropping deliveries. That gives real context for the main decision an agent faces (grace period or not), though it never states when-not to rotate or that other webhook tools exist for non-secret changes.

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