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

Beyond the annotations (readOnlyHint, idempotentHint, destructiveHint), the description adds valuable behavioral detail: no credits are spent, results are a [min_credits, max_credits] range, costs are data-dependent, and specific free-call cases are given. This goes well beyond the structured safety hints and enriches the agent's mental model.

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 accomplish all goals: purpose, behavior, and usage example. Nothing is redundant; every sentence carries essential information. The structure is front-loaded with the core function and then elaborates with context and a concrete example.

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?

Given the tool's moderate complexity (array input, max 50 items) and the presence of an output schema, the description fully covers what an agent needs to invoke it correctly: the input format, the output format (range), and special cost edge cases. No critical information is missing.

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?

With 0% schema description coverage, the description fully compensates by explaining the required 'calls' array structure, the 'tool' and 'arguments' fields, and providing a concrete JSON example. The agent knows exactly what to pass without needing to infer from a bare 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 opens with a specific verb ('Estimate') and resource ('credit cost of planned tool calls'), making it unmistakable. It explicitly states 'before making them' and 'no credits are spent,' distinguishing it from all sibling tools that actually fetch data. This is a model of clear purpose differentiation.

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 clearly conveys when to use the tool (before executing calls, to estimate cost) and provides a usage example. However, it does not explicitly state when not to use it or name alternatives. The context makes the use case obvious, but explicit exclusion guidance is missing.

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