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

Annotations already declare the tool is not read-only, is idempotent, and is non-destructive. The description adds valuable domain behavior beyond those annotations: exhausted accounts cause cables to go dark on all lines, and 429 is a temporary jam rather than exhaustion.

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?

Two compact sentences, front-loaded with the reporting action and followed by the critical exhaustion rule. The phrase 'with source and hour' is slightly ambiguous because the schema uses a window enum rather than an hour parameter.

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?

Covers the important operational semantics for an agent: how to interpret 402, 429, monthly_cap, and used_pct 100. With no output schema, it could say more about what the tool returns or how reset_at and exhausted interact, but the core behavior is adequately conveyed.

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 100%, so the schema already documents all six parameters, including the error_code enum and used_pct semantics. The description reinforces the high-stakes exhaustion logic but largely repeats what the schema already states.

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 and resource: reporting a limit reading for the model account of a cable from the owner's machine. The examples (get_usage, Codex rate limits, provider 402/429) make the domain concrete and clearly distinguish this from sibling messaging/line tools.

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?

Explains the meaning of 402/monthly_cap versus 429, which helps an agent interpret a reading. However, it does not explicitly state when to call this tool versus alternatives, nor what prerequisites must be true before reporting.

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