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

readOnlyHint=true already tells the agent this is a safe read; the description adds the newest-first ordering and the scoping to a single application, plus the REST path. Pagination is only implied via schema's iterator field, and no rate-limit or content-size behavior is disclosed.

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 front-loading scope and ordering, then filters, then the REST endpoint. No filler, though the REST path is of marginal value to an agent invoking an MCP tool.

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 nine-parameter list tool with no output schema, the description omits return shape and pagination workflow (iterator/limit usage), which the agent must infer from the schema. Annotations cover safety, but pagination guidance 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 all nine parameters are documented in the schema itself. The description echoes the filter set (event type, channel, tag, time window) without adding format details, 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 (List) and resource (webhook messages) scoped to one application, with an ordering guarantee (newest first). It does not name or distinguish itself from the closest sibling, svix_list_endpoint_messages, which narrows messages to a single endpoint.

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 filter dimensions (event type, channel, tag, time window) give implicit guidance on when the tool applies, but there is no explicit when-not and no routing to alternatives such as svix_list_endpoint_messages for endpoint-scoped listings.

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