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

Annotations already cover readOnly, idempotent and non-destructive, but the description adds real value: it names the returned fields (balance_credits, available_credits, reserved_credits, USD strings, ledger_source) and explicitly rules out funding/reserving/moving/spending. That negative scope is the key behavioral disclosure.

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 tight sentences, front-loaded with the action and scope, then the return shape, then the exclusions. No filler.

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 no output schema, the description carries the return-value burden and does so by enumerating the balance fields and ledger_source. Combined with the explicit mutation exclusions, an agent has everything needed to call it and interpret the result.

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?

Zero parameters, so there is nothing to disambiguate; baseline is 4. The description correctly avoids inventing argument semantics for a no-arg tool.

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 ("Read") and resource ("shared credit wallet") and clarifies scope with "authoritative" and "no new payment." It distinguishes itself from payment siblings implicitly via the negative clauses, but never names an alternative tool the way a 5 would.

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?

"Read your authoritative shared credit wallet; no new payment" plus "does not fund, reserve, move or spend credits" gives clear when-to-use and when-not-to-use context. It stops short of naming which sibling to use instead for funding or transferring.

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