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

The only annotation is destructiveHint=true, so the description carries most of the behavioral burden. It adds genuinely useful context beyond the annotation: delivery goes to real customer URLs, and the message fans out across all subscribed endpoints. It still omits retry/async semantics and any auth or rate-limit notes.

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 tight, front-loaded sentences with zero filler. The trailing 'Svix REST: POST /api/v1/app/{app_id}/msg' line is mildly redundant for an agent already calling the MCP tool, but it is brief and harmless.

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 tool with no output schema and a nested payload object, the description conveys purpose, scope, and external side effects adequately. It stops short of describing what comes back (e.g., a message id) or how event_id idempotency behaves on repeat calls.

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% — app_id, event_type, payload, tags, channels, and event_id are all documented in the schema itself. The description adds no parameter-level meaning beyond that, so the baseline of 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?

States a specific verb and resource ('Send a webhook message') plus precise 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_list_endpoint_messages without needing to name them.

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?

Usage is implied by the description — publish an event to subscribers — and the note that it 'delivers real traffic to your customers' URLs' signals a production side effect. However, it never states when to prefer svix_resend_message or svix_list_messages instead, nor any prerequisite about the event type needing to exist in the app.

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