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

Beyond the readOnlyHint/openWorldHint annotations, the description discloses a sign-in requirement, free versus Premium daily search quotas, parallel fan-out behavior, the coverage field, and the fact that unavailable airlines are omitted from the fan-out. This gives an agent a realistic model of what happens at call time without repeating annotation data.

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 dense sentences each earn their place: the core action, the live-list caveat, the alternative tool routing, and account/auth constraints. The description is front-loaded with the most important information and avoids 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?

For a complex parallel search tool with no output schema, the description covers sign-in, quotas, airline-source caveats, the coverage field, and the grouped-by-airline response shape. The main remaining gap is that the full result item structure is not specified, but the description still gives an agent enough to invoke and interpret the 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?

The schema already describes all parameters (100% coverage), so the baseline is 3. The description adds account-tier behavior relevant to the cabin parameter ('Free accounts get 3 economy searches/day; Premium ... gets unlimited searches across every cabin') and frames the required parameters as a route-and-date parallel search, which slightly enriches the schema without replacing it.

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 states exactly what the tool does: 'Search award flight availability across every airline currently LIVE for a route and date, in parallel.' It also distinguishes itself from the single-airline sibling by naming search_availability and identifying itself as the recommended starting point, so no agent confusion remains.

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?

Explicit when-to-use guidance is present: 'This is the recommended starting point — use single-airline search only if you need a specific airline.' It further clarifies when airlines are skipped (source down, blocked, or login-walled) and points to list_supported_airlines and search_availability as supporting alternatives.

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