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

Annotations already mark the tool read-only, and the description adds meaningful semantics: totalMins can legitimately differ from deductedMins, period.source defines the window type, and outboundBlockedReason distinguishes exhausted minutes from a missing plan. This helps an agent interpret the response correctly.

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?

Five sentences packed with caveats and field semantics, with the core purpose front-loaded in the first sentence. Every sentence contributes either invocation guidance or interpretation context.

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 zero-parameter read-only tool with an output schema, the description fully covers how to know whether usage is exhausted or missing a plan, how period.source should be interpreted, and why totals differ. Nothing needed to invoke or interpret the tool 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?

The input schema has zero parameters, so there is no parameter meaning for the description to add; the 0-parameter baseline applies. No parameter details are present, but none are needed for invocation.

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 precise resource and result set: the organization's current plan, minutes balance, minutes spent, and days left in the billing period. It distinguishes the tool from list_calls by warning not to estimate balance, spend, plan, or renewal from call records.

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 explicitly directs agents to read this before answering anything about balance, spend, plan, or renewal and instructs them to never estimate those values from list_calls. It also gives conditional guidance for reconciled Outreach data, which is more than is strictly required.

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