Estimate LINE send cost

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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, so the safety profile is clear. The description adds meaningful behavioral details: it explains the cost formula (message_count × recipients), how recipient counts are derived for different target types, and that results are unknown for filter/everyone. This goes beyond the annotations without contradicting them, though it omits potential edge cases like quota exhaustion behavior.

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 three well-structured sentences that front-load the primary purpose. Each sentence adds value: the first states what it does, the second explains the key input semantics, the third discloses output format. No word is wasted, and the formatting is easily scannable.

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?

The description covers the essential aspects: purpose, usage context, parameter nuances, and return format. It even mentions the recommended alternative for a specific case. Given the rich schema for target and the explicit output shape, the description is fully adequate for the tool's complexity. Sibling tools are effectively differentiated.

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 low (33%), but the description compensates significantly. It explains that 'target uses the same shapes as line_send_message' and clarifies the semantic meaning of message_count ('LINE charges message_count × recipients'). It also describes how the target type affects the accuracy of recipient estimation. The 'oa' parameter is not explained, but the description still adds substantial meaning beyond the 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+resource: 'Estimate how many quota messages a planned send will consume, without sending.' It clearly distinguishes itself from the related sibling line_send_message, which actually sends messages. The purpose is unambiguous and includes the key qualifier that it is for estimation only.

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?

The description explicitly states when to use this tool ('before confirmation, especially for narrowcast/broadcast') and when not to ('without sending'). It also provides an alternative for an unsupported case: for filter/everyone targets, it recommends line_send_message dry_run instead. This gives the agent clear decision criteria.

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