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

Annotations already declare readOnlyHint=true, so safety is covered. The description adds that each returned message carries its delivery status, which is useful context beyond the annotations, but it says nothing about ordering, default page size behavior, or cursor semantics (those live only in the schema).

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 sentences: the semantic purpose is front-loaded first, the API mapping second. No filler, no restatement of the title, and the delivery-status detail is packed into the opening clause.

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 does state what a caller gets back (messages plus per-message delivery status) and the schema fully documents pagination. Minor gaps remain: no mention of ordering or whether results can be filtered by status, but nothing essential to invoking it correctly 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%, including limit range, iterator cursor semantics, and id/uid acceptance for both ids, so the schema carries the parameter burden. The description merely echoes app_id and endpoint_id in the URL template and adds no format or validation detail beyond it.

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?

Specific verb and resource with an explicit scope qualifier: 'messages destined for one endpoint, with each message's delivery status.' The endpoint scoping implicitly distinguishes it from the app-wide svix_list_messages, but the sibling is never named, so an agent must infer the split.

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 only implied by the endpoint-scoped framing; there is no explicit when-to-use versus svix_list_messages, svix_get_message, or svix_list_attempts_by_endpoint. The REST path mapping hints at the resource relationship but is not guidance.

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