Account balance

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

The annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so safety is covered. The description adds value beyond them by decoding the fields returned, defining the credit unit (1 credit = $0.01) and explaining escrow/pending/holds/available, plus the zero-cost signal that no annotation conveys.

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?

One sentence, front-loaded with the resource being read, then a compact parenthetical that defines each sub-field. The parenthetical is dense but every clause maps to a returned value; only the terminal "Free." is slightly terse relative to its usefulness.

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 burden of explaining returns, and it enumerates credits, unsettled debt, prepaid account and payment rail along with the four credit sub-buckets. It does not describe the response envelope, ordering, or units for debt/prepaid fields, a small residual gap for a zero-parameter read.

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 no parameters, so there is no per-argument semantics to explain and the baseline of 4 applies. The description does not waste words on arguments that do not exist.

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?

"Spendable balance of the Carpe Diem account behind CARPE_API_KEY" names a concrete resource and the credential it belongs to, and it distinguishes the subject from usage-focused siblings like carpe_usage_summary or carpe_key_usage. It stops short of explicitly naming a sibling it replaces, so an agent must infer the balance-vs-usage split.

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: a spendable balance suggests a pre-flight check before paid calls, and the trailing "Free." signals it can be called without cost. There is no explicit when-to-use, no when-not-to-use, and no mention of when carpe_usage_history or carpe_session_spend would be the better call.

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