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

Beyond the annotations (readOnly/openWorld/non-idempotent/non-destructive), it discloses non-obvious behavior: cached ideas get re-checked availability, unknown availability and missing quotes are returned as null and never reused from stale searches, premium vs standard pricing rules, and an approximate one-minute generation latency with a retry_after_seconds loop. That is substantial context the annotations cannot convey.

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?

Purpose and return content are front-loaded, and every clause carries real information (null semantics, pricing, retry). The caching/pricing sentences are dense and slightly overpacked, but nothing is redundant filler.

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?

There is no output schema, so the description carries return-value duty and does so reasonably: names, availability, search volume, null placeholders, and the 'generating' status with retry_after_seconds. It leaves the exact response shape partially implied, and does not touch the other sibling, but an agent has enough to call and re-call correctly.

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 (idea, tlds, purpose, description) are already documented in the schema, including the omit-to-auto-pick behavior for tlds. The description adds only incidental semantics (output includes domain hacks and search volume) and no parameter-level detail beyond the schema, 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?

The first sentence states a specific verb ('Brainstorm') plus resource ('domain names') and the input subject ('an idea, product, or company'). The second sentence sharpens scope by naming the output ('brandable names and any domain hacks'), which plainly separates it from a per-name availability lookup.

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 routes the agent to the sibling search_domain for a fresh per-name quote, which is explicit alternative selection, and it gives concrete retry instructions for the 'generating' status. It never addresses check_availability or states a when-not-to-use condition, so it stops short of full coverage.

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