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

Annotations already cover readOnly/idempotent/destructive safety, and the description adds genuinely new behavioral facts on top: parallel calls are rejected and return no data, and a failed check does not count as available. The concurrency restriction and failure semantics are exactly the kind of context annotations cannot express.

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-loads purpose, then the concurrency constraint, then the value glossary, so a reader can stop early if they only need the summary. The value glossary is slightly long, and some of it may overlap with the output schema, but each sentence carries information.

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 single-parameter, read-only, output-schema-backed tool, the description covers purpose, batching limit, concurrency rules, result-value semantics, and failure handling. Nothing an agent needs in order to call it correctly is missing.

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 coverage is 100% and there is only one parameter, so the schema already documents the comma-separated FQDN format and the 50-domain maximum. The description restates the 50-domain limit but adds no new syntax or formatting detail. Baseline 3 is appropriate 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?

States a specific verb and resource ('Check the registration status of domains') with an explicit scope of 'up to 50 domains at a point in time.' An agent can immediately tell this is the batch variant of a single-domain check, though the description never names the sibling 'available' or 'bulk_tld' to make the routing 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 clear operational guidance: concurrent calls are not supported, send one batch, wait for the result, then send the next. This tells the agent how and when this tool may be invoked (serial use only). It stops short of naming an alternative tool for single-domain or TLD-specific checks, so it is not a full 5.

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