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

Annotations only declare readOnlyHint and openWorldHint; the description adds genuinely useful behavioral context beyond that — the trust model ('only trusted while it still calls a certainly-taken name taken'), and the degraded-result behavior for platforms that refuse checks (Instagram, TikTok, Facebook, Reddit return 'check yourself' with a link). It omits latency, rate limits, and partial-failure handling, so it is strong but not exhaustive.

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?

Three sentences, front-loaded with what is checked and how many platforms, then the reliability caveat, then the cost model. Every sentence carries distinct information with no 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?

With one well-documented parameter and no output schema, the description does the heavy lifting on results by explaining the 'check yourself' fallback shape. It could say more about what a successful result contains (per-platform statuses) and about partial failures, but it is sufficient for correct invocation.

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% and the schema already supplies the format example ('rosiebakes' or '@rosie_bakes'), so the baseline is 3. The description's 'brand name or username' phrasing adds no syntax or normalization detail beyond what the schema provides.

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) and resource (brand name/username availability) with concrete scope: 29 named platforms plus domain endings. An agent can immediately tell this is a cross-platform availability lookup, distinct from the app-management siblings (app_status, create_app, list_apps).

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 operating context — free, no API key needed, and the coverage list — which helps an agent decide this is the right call for name availability. It does not, however, state any explicit when-not-to-use condition or point to an alternative tool, so it stops short of full routing guidance.

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