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

The readOnlyHint annotation already establishes this is a safe read, and the GET /api/v1/... path in the description reinforces that. The description adds the payload-inclusion behavior, but says nothing about auth requirements, error cases (missing message), or whether content can be omitted by default.

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 with the purpose front-loaded and the REST mapping appended for orientation. Nothing is wasted, though the endpoint path is arguably redundant given the tool name convention.

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?

There is no output schema, so the description usefully signals that the response includes event type and payload. Combined with full schema coverage and a readOnly annotation, this is nearly complete; only error/auth behavior is absent.

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 app_id, msg_id, and with_content are all documented in the schema itself. The description adds no parameter-level meaning beyond what the schema provides, so the 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?

States a specific verb and resource ("Fetch a single message") and identifies what comes back (event type and payload). The word "single" implicitly contrasts with the list_messages sibling, though no sibling is named explicitly.

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: an agent infers this is for retrieving one known message rather than enumerating. There is no explicit when-to-use-vs-alternatives statement, no mention of when to prefer svix_list_messages or svix_list_attempts_by_message instead.

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