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 behavior annotations don't: results span all endpoints and include status, response code and body, which tells the agent what it will actually get back. Pagination behavior is left to the schema.

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 purpose sentences plus the canonical REST path, with the most decision-relevant information (what it lists, why you'd call it) front-loaded. No filler sentences.

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 partly compensates by naming the returned fields (status, response code, body). Required params and pagination cursor are fully covered by the schema, so an agent has enough to invoke correctly; only return-shape detail like response structure/pagination envelope is unaddressed.

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 every parameter (limit, status, iterator, endpoint_id, status_code_class) is already documented with ranges and semantics. The description adds no parameter-level meaning beyond the 'across endpoints' framing, which is the correct baseline when the schema does the heavy lifting.

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?

Specific verb and resource ('List every delivery attempt Svix made for one message'), plus the scope qualifier 'across endpoints', which implicitly contrasts with the sibling svix_list_attempts_by_endpoint. It never names that sibling, so the differentiation is inferential 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?

Gives a concrete use scenario — answering 'why did this webhook not arrive?' — which tells the agent exactly when this tool is the right pick. It does not state when to prefer svix_list_attempts_by_endpoint or svix_get_message instead, so no exclusions are provided.

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