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

With no annotations, the description carries the full burden, and it discloses only that money is charged and a balance credited. It says nothing about irreversibility, refunds, double-charge protection via the idempotency_key, failure modes such as a missing stored method or declined charge, or whether the ledger update is atomic with the charge.

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 well-formed sentence with the charge action front-loaded and no filler. It is efficient, though the efficiency comes partly at the cost of the missing detail noted above rather than genuine density.

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 values need not be described, but this is an unannotated financial mutation with three undocumented parameters and a sibling tool it never distinguishes itself from. Key information an agent needs to call it safely is absent.

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 all three parameters, so the description must compensate and does not: it never explains the unit or bounds of 'credits', the purpose of the 'description' field, or the critical semantics of 'idempotency_key' (empty default implies no protection unless supplied). An agent could easily mis-set credits or omit the idempotency key and cause a duplicate charge.

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 ('Charge') and the exact resource ('the caller's stored payment method'), plus the resulting effect ('credit the legacy tenant balance'). It implicitly contrasts with purchase_credits_with_card by specifying the stored method rather than a supplied card, but never names that sibling, so disambiguation is left to inference.

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?

There is no statement of when to use this versus purchase_credits_with_card, register_billing_payment_method, or get_billing_status. The phrase 'stored payment method' hints that a method must already be registered, but no prerequisite, exclusion, or alternative is spelled out for a tool that moves real money.

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