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

readOnlyHint=true already tells the agent this is a safe read, so the description only needs incremental value. It adds that each row includes delivery status and gives the underlying REST path, which is helpful, but says nothing about pagination behavior, result volume, or ordering beyond what the schema's iterator/limit params already convey.

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 compact sentences: the scoping/return content comes first, the REST route second as a reference. No filler and nothing that restates the title verbatim.

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 4-parameter read-only list tool with no output schema, the description covers purpose, scope, and the key returned field (delivery status) while the schema handles all parameters. It is adequate; only minor gaps like pagination/ordering expectations remain.

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, endpoint_id, limit, and iterator are all documented in the schema itself, and limit's default of 50 is stated there. The description's REST path reinforces which ids are required but adds no format or behavior detail beyond the schema, 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 (List) and resource (messages) and narrows the scope with 'destined for one endpoint', which meaningfully separates it from svix_list_messages. It also says the result carries delivery status. It stops short of naming the sibling it should be preferred over, so sibling differentiation is implied rather than explicit.

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 phrase 'destined for one endpoint' implies you use this when you want messages scoped to a single endpoint, which is useful context, but there is no explicit when-to-use/when-not or named alternative (e.g. svix_list_messages for all messages). Usage must be inferred from scope language alone.

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