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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so safety is covered. The description adds genuinely useful behavior beyond that: newest-first ordering, a 500-per-page cap, and the RRset grouping rule. It does not mention rate limiting or auth requirements, but that is a minor gap given the annotation coverage.

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?

Four short sentences, each earning its place: purpose and RRset definition front-loaded, then filtering, then pagination, then the endpoint. No filler or redundancy.

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 carries the burden of describing returns, and it does so reasonably by defining an RRset and noting newest-first order and page size. It omits what fields each returned RRset carries (ttl, records, type, subname), which is the only notable gap for a list tool.

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 four parameters (type, cursor, domain, subname) are already well documented in the schema, including the cursor's next_cursor origin and the '@' apex convention. The description only restates the type/subname filters and adds no format or syntax detail beyond the schema. Baseline 3 is correct.

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 gives a specific verb (List) and resource (DNS records of a domain as RRsets) and even defines what an RRset is — 'all records of one name and type, sharing one TTL' — which cleanly separates it from desec_get_rrset (singular). It stops short of naming or contrasting any sibling explicitly, so it lands at 4 rather than 5.

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?

It states that you can 'Filter by type and/or subname' and the schema notes omitting subname includes every subname, so usage is implied. There is no explicit when-to-use-this-vs-alternatives guidance (e.g., list vs get_rrset vs export_zonefile), leaving the agent to infer.

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