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

Annotations already declare readOnlyHint=true and openWorldHint=false, so safety is covered. The description adds real behavioral value by naming the three balance components, including the subtle 'part held by running jobs', which tells the agent why total and spendable differ.

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 tight sentences that front-load the core meaning and end with the parameter-discovery hint. The middle sentence on customer.quotas is slightly ambiguous in referent but not wasteful.

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?

With an output schema present, the description need not document return values, and it still summarizes the balance breakdown helpfully. Combined with the customer_id sourcing hint, an agent has what it needs to call this correctly; only edge-case behavior (e.g. missing customer) is unaddressed.

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 0% for the single customer_id parameter, and the description does compensate partially by saying where to obtain it ('customer_id is in scout_list_projects'). That is genuine provenance information the schema lacks, but it stops short of format or expected-value details.

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 ('Get the prepaid balance of a customer') and even decomposes the result into total, held-by-jobs, and spendable. It does not contrast itself with a sibling, but none of the listed siblings overlaps in purpose, so the risk of confusion is low.

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?

Usage is only implied: an agent infers it should call this to check spendable funds before spending on analyses. There is no explicit when-to-use or when-not-to-use statement, and the reference to customer.quotas reads as a pointer but is ambiguous about whether it describes the response or another data source.

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