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

readOnlyHint=true already covers the safety profile, so the bar is lower; the description adds real value by disclosing the shape of the result (counts bucketed by success/pending/sending/fail) even though there is no output schema. It does not mention auth requirements or the default time window, which is the remaining gap.

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?

Front-loaded with the verb and resource, then the value proposition, then the REST path — no filler sentences. The 'Svix REST: GET ...' clause is useful for API parity but slightly extraneous for an agent that already has the schema.

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 simple read tool with no output schema, the description supplies the return-field breakdown and the API path, which is nearly enough to call it correctly. The only real omission is what window is used when the optional since/until parameters are left out.

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, endpoint_id, since and until are already documented with formats and examples. The description adds nothing about the optional time-window parameters (e.g. default range when since/until are omitted), so it sits at the baseline 3.

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 ('Read delivery statistics for one endpoint') and even enumerates the returned counters (success, pending, sending, fail), so an agent knows exactly what comes back. It does not name or contrast with any sibling (e.g. svix_health, svix_list_attempts_by_endpoint), which keeps it out of 5 territory.

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 fastest way to see whether an endpoint is healthy' implies a use case, but no explicit when-to-use/when-not guidance and no alternative is named. An agent can infer this is the quick health-check call, but must still guess how it relates to svix_list_attempts_by_endpoint or svix_health.

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