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

Annotations only declare destructiveHint=true; the description adds genuinely useful behavioral context by disclosing that this fires real delivery traffic at customer URLs, which is exactly the kind of consequence an agent needs to weigh before calling. It still omits auth requirements, delivery guarantees, and idempotency behavior despite an event_id parameter existing, so it is not complete.

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 sentences that are front-loaded with purpose and the important side-effect warning. The trailing 'Svix REST: POST /api/v1/app/{app_id}/msg.' is marginally redundant for an agent but confirms the underlying operation.

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 should ideally say something about the response (e.g. a message id) and failure/retry behavior; it does not. It does, however, fully cover what the tool does and its real-world impact for a 6-parameter mutation, so the gap is moderate rather than severe.

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 explains app_id, event_type, payload, tags, channels, and event_id. The description adds nothing about parameter syntax, formats, or interactions (e.g. how channels restricts delivery), so baseline 3 applies.

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 (send) and resource (webhook message) and pins down the fan-out scope: 'to every endpoint of an application subscribed to the event type.' This distinguishes it from siblings like svix_resend_message and svix_get_message without needing to open their schemas.

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 sentence 'This delivers real traffic to your customers' URLs' implies the tool has real-world side effects and should be used deliberately, but there is no explicit when-to-use guidance, no mention of prerequisites, and no direct comparison to alternatives such as resend_message.

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