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

Annotations already declare write (readOnlyHint=false), non-destructive, and closed-world operation. The description adds meaningful behavior beyond that: the upsert semantics, the PUT/POST selection rule, and the create-time required fields. It omits auth requirements and side effects of updates, but adds real value over the structured fields.

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 tight sentences, front-loaded with the upsert framing. Every clause earns its place and none 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 an 8-parameter write tool with 100% schema coverage and an output schema, the description covers the essential mode-selection semantics and the declarative use case. It could mention auth/signature expectations, but those live in the schema, so nothing critical is missing.

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 id, url, events, and the rest. The description restates the id→PUT/omitted→POST rule and the create-time required fields, but adds no syntax or format detail beyond what the schema provides. Baseline 3 is correct.

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+resource ('Create or update a webhook subscription') and immediately clarifies the upsert branch logic: id present = PUT update, id omitted = POST create. An agent can tell exactly what the tool does and how the mode is selected without opening the 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?

Explicitly frames the tool for declarative 'ensure webhook X exists' workflows, which tells the agent when this is the right choice versus a plain create. It doesn't name the alternatives (e.g., webhook_delete for removal, webhook_test for verification), so it stops short of full when-not guidance.

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