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

Goes well beyond the annotations by disclosing early enrichment termination (premium may stay null), partial-failure semantics (answers received plus retry guidance, no automatic retries), and that cachedOnly performs no provider calls — behavior an agent cannot infer from readOnlyHint=false / openWorldHint=true alone. This explains why the call is not read-only or idempotent: it hits external providers and can partially fail.

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?

Five tight sentences, each carrying distinct information (scope, enrichment cutoff, failure behavior, cache mode, out-of-scope features) with the core capability front-loaded. No filler or restatement of the title.

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 3-parameter tool with no output schema, the description covers the ambiguous outcome cases that matter most: null premiums, partial results with retry guidance, and cache-miss behavior. It stops short of describing the shape of a per-extension result, which is a minor gap given no output schema exists.

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 already 100%, so the baseline is 3, but the description adds real meaning for cachedOnly ('makes no provider calls', cache misses stay unconfirmed) and restates the 20-extension cap on tlds. It does not add anything for the name parameter beyond the schema's own explanation.

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 (check), resource (one name's availability), and explicit scope (up to 20 extensions, reusing shared evidence), which implicitly separates it from the single-extension check_availability sibling. The closing negative scope ('No selected-registrar fallback, fresh mode, prices or purchases') further fences it off from get_registrar_link/get_tld_prices/estimate_cost.

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 when-not guidance — no registrar fallback, no fresh mode, no prices or purchases — which steers the agent to the price and purchase siblings. It also explains that cachedOnly is the zero-provider-call mode. What it lacks is any explicit 'use this instead of check_availability when you need >1 extension' routing statement.

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