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

Beyond the readOnly/idempotent/non-destructive annotations, the description adds valuable behavioral context: it returns estimates only, does not execute the operation, gives exact or ranged prices depending on channel/outcome, does not promise accuracy percentages, and is free/no-key with ~100ms latency. No annotation contradiction.

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?

The description is front-loaded with the core purpose, then organized into examples, usage guidance, and operational notes. Every section adds necessary information, and the structure makes it easy for an agent to parse quickly.

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 two-parameter preview tool with no output schema, the description covers return value shape (cost, latency, success probability, exact vs. range), parameter usage via examples, usage constraints, caching guidance, cost, latency, and key requirements. An agent has enough context to invoke it 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 coverage is only 50% (operation lacks a description), but the description compensates with two concrete examples showing operation values ('send_message', 'schedule_appointment') and params shapes ('preferred_channel'). It also clarifies that params is 'the same request body you would pass to the operation', adding meaning beyond the raw schema.

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 a specific verb ('Return') and resource: expected cost, latency, and success-probability estimates for a proposed call before execution. It clearly distinguishes the tool from operational siblings by framing it as a pre-execution estimation step, and clarifies exact vs. range pricing.

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 provides explicit WHEN TO USE (budget constraint, deciding whether to proceed) and WHEN NOT TO USE (hot loop, cache for 60 seconds), plus concrete example queries. It does not name alternative tools, but the usage boundaries are clear and actionable.

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