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

Annotations already declare readOnlyHint=true, so the safety profile is covered. The description adds useful context — the exact REST resource path and the four counter buckets returned — but says nothing about the default time window when since/until are omitted or whether counts are windowed or all-time, which materially affects interpretation of the numbers.

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 — what it returns first, health-check framing second, REST path last — with no filler. Every clause carries information an agent can use.

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 the right thing by naming the returned counters. The remaining gap is the time-window behavior of the optional since/until parameters, which an agent must guess before calling.

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 all documented in the schema itself. The description adds nothing about the since/until semantics (defaults, maximum range, required pairing), 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 ('Read delivery statistics for one endpoint') and enumerates the returned metrics (success, pending, sending, fail), which no sibling tool offers — svix_list_attempts_by_endpoint returns attempt-level records, not aggregates. An agent can distinguish this from every sibling without opening the schema.

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' gives a clear situation in which to reach for this tool, but offers no exclusions and never names the alternative (e.g. listing attempts) for when per-attempt detail is actually needed. Context is present; routing guidance is not.

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