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

With no annotations, the description carries the full behavioral burden and does substantial work: it defines balance = available + reserved, guarantees non-negativity, explains that reserved represents estimated fees of open invoices paid with credits, and states the redemption formula (≈30 bps of fiat, floor 2, cap 2000). It stops short of saying this is read-only or what the response looks like when no wallet exists.

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 sentences, front-loaded with the core return shape, then the pricing/consumption model that an agent needs to interpret the numbers. The dense field enumeration is load-bearing because there is no output schema to document it.

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?

Because there is no output schema and no parameters, the description must define the return fields and their units, and it does — including the credit-as-$0.01 conversion so values are interpretable. It omits edge behavior such as the response when no credit wallet exists, which would round it out.

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 the baseline is 4. The description correctly adds no parameter discussion and instead spends its words on the return payload, which is the right allocation here.

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+resource — return the merchant's prepaid processing-credit balance — and immediately enumerates the returned fields, which cleanly separates it from siblings like create_credit_purchase and list_credit_bundles. An agent can tell this is the read-side of the credit lifecycle without opening any schema.

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: it is a zero-argument read of current credit state, so invocation itself is unambiguous. But nothing states when to prefer this over get_records_summary or get_rates, nor any precondition such as requiring an existing wallet, and no alternatives are named.

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