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

Annotations already declare readOnlyHint=false, destructiveHint=false, and idempotentHint=true. The description adds valuable behavioral context: 'Only provided fields change' (partial update semantics) and 'Re-enabling clears the failure counter' (a side effect not obvious from the schema). This goes beyond what annotations provide.

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 with zero waste. The first sentence lists the mutable fields, the second clarifies partial-update semantics, and the third adds the failure-counter side effect. Every sentence earns its place and the most important information is front-loaded.

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 update tool with 100% schema coverage and an output schema, the description is nearly complete. It covers the core semantics (partial update, re-enable behavior). It doesn't mention idempotency_key behavior, but the schema already documents that thoroughly. The only minor gap is not explicitly stating that endpoint_id is required, but the schema's 'required' field covers that.

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 all 7 parameters thoroughly. The description adds the partial-update semantics ('Only provided fields change') and the re-enabling side effect, but doesn't need to repeat parameter details. Baseline 3 is appropriate since the schema does the heavy lifting.

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?

The description states a specific verb ('Change') and resource ('a webhook's url, events, account_ids, description or is_active'), clearly distinguishing it from create_webhook_endpoint, delete_webhook_endpoint, list_webhook_endpoints, and test_webhook_endpoint. It also adds the key semantic that only provided fields change, which is essential for an update operation.

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 implies when to use this tool: when you need to modify an existing webhook endpoint's fields. It doesn't explicitly name alternatives or exclusions, but the sibling list makes the distinction clear (create vs update vs delete vs test). The 'Only provided fields change' line gives important usage context for partial updates.

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