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

Goes well beyond the annotations: it discloses that the HMAC signing secret is returned EXACTLY ONCE and must be stored immediately, that a human approver (not the agent) sees the secret, and that internal/loopback targets are refused. Annotations only mark it as non-readOnly, destructive and non-idempotent; the description supplies the operationally critical behavior.

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?

Purpose is front-loaded in the first clause and every sentence carries information, but the second sentence is grammatically awkward ('Respondent answers then leave Fillo for an endpoint Fillo does not control'), costing some readability.

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 an output schema present, return values need not be explained, and the description still covers the one-time secret, the approval flow, and the loopback refusal. It is nearly complete for a 4-parameter mutation tool; only explicit sibling routing 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 baseline is 3. The description restates the outbound credential (bearer or x-api-key) and the abandoned-events default, which mirrors the schema rather than adding new syntax or constraints.

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?

Opens with a specific verb+resource: 'Add a signed webhook to a form.' The agent can distinguish this from sibling webhook tools (fillo_list_webhooks, fillo_update_webhook, fillo_remove_webhook) by the verb. It stops short of explicitly naming those siblings, so it is clear but not fully differentiated.

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?

Provides context about the human-approval flow and the optional draft.abandoned events, which implies when the tool fits. However, it never states when to use this versus fillo_update_webhook or fillo_list_webhooks, nor any prerequisites, so usage is only implied.

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