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

The description labels the operation "(additive)", while the annotation declares destructiveHint=true — the MCP vocabulary explicitly defines additive as the opposite of destructive, so these signals conflict. The description does add genuinely useful behavior (an outbound POST to target_url fires on the chosen event, mapped to POST /webhooks/), so it is not a total void, but the contradiction undercuts the safety profile.

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 short, front-loaded clauses with no filler: the action, the runtime behavior, and the REST mapping. The endpoint mapping earns its place, though the parenthetical "(additive)" is the weakest element given it conflicts with the annotation.

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-type tool with no output schema and no annotation beyond destructiveHint, the description covers the core effect but omits what is returned (e.g., webhook ID for later management), any auth/scope requirements, and the interaction with existing subscriptions. Adequate to invoke, but not complete.

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 all three parameters (target_url, event with default "file.uploaded", is_active with default true) are already documented in the schema. The description only restates that target_url receives a POST and that the "chosen event" triggers it, adding no syntax, format, or default information beyond the schema.

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?

"Creates a webhook subscription" is a specific verb+resource, and the description goes further by naming the REST endpoint (POST /webhooks/) and clarifying that the operation is additive. It is clearly distinct from the sibling list_webhooks, but it never explicitly references that counterpart, so differentiation is inferred rather than stated.

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 description explains the mechanics (the project POSTs to target_url when the chosen event fires) but gives no guidance on when to use this tool versus alternatives, no prerequisites, and no warning that repeated calls accumulate subscriptions. Usage is only implied by the tool name.

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