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

Annotations already establish read-only, non-destructive, closed-world behavior. The description adds non-obvious semantics: subscription credits expire at period end, and the balance should not be assumed sufficient without consulting bySource. It does not cover auth requirements, but that is a minor gap for a read-only numeric lookup.

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?

Front-loaded with the resource and scope, and each clause carries distinct information (equivalence, use case, expiry caveat, cost). The trailing 'Free.' fragment is slightly abrupt but delivers useful cost 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?

An output schema exists, so return-value documentation is not required; the description still flags the bySource field as the thing to inspect. For a no-param read-only lookup, the agent has everything needed to call and interpret it.

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 tool takes zero parameters, so there is no parameter semantics for the description to add. Baseline for a parameterless tool is 4.

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 resource (account-wide spendable credit balance) with scope qualifiers (shared by India and US APIs) and explicitly clarifies it is not a separate India allowance. An agent can distinguish this from get_credit_balance purely from the description.

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?

Gives an explicit use case (pre-flight checks, low-balance alerts from an India workflow) and names the equivalent sibling tool, so the agent knows this is not a distinct allowance worth querying separately. Nothing about when to reach for it is left to inference.

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