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

Annotations already declare this is a non-read-only, non-destructive, closed-world mutation, so the safety bar is partly covered. The description adds the meaningful extras of owner-only auth and a manual verification precondition, but says nothing about idempotency, whether negative or zero credits are accepted, audit logging via tx_note, or what happens on failure.

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?

A single front-loaded sentence that leads with the authorization scope and ends with the precondition. Nothing is redundant or padded.

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 credit-granting mutation with no output schema, zero documented parameters, and two easily confused key parameters, the description leaves too much unspecified. An agent cannot tell which key receives credits, what tx_note is for, or what the result looks like.

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 description coverage is 0%, so the description must carry all parameter meaning and it carries none. The distinction between api_key (caller's key) and target_key (customer's key) is exactly what an agent could get wrong, and tx_note is never mentioned.

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 ('Add credits to a customer key') plus a precondition, which is far more informative than the title alone. It only implicitly distinguishes itself from the read-only sibling check_credits, so sibling differentiation is not explicit.

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 both an authorization constraint ('Owner only') and a triggering condition ('after verifying their crypto payment'), which is enough for an agent to know when this applies. It stops short of naming the alternative tool or stating what to do when the payment is unverified or the key is invalid.

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