List the sandbox test values (test mode only)

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

Annotations already cover safety (readOnly, idempotent, non-destructive, closed-world), and the description adds real context beyond them: the auth requirement for a test key, the exact failure mode with a live key (`403 test_mode_only`), and an enumeration of the outcomes each value triggers (declined, processing→succeeded, processing→failed, timeout, not found).

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?

Front-loaded with the headline and the test-mode constraint, then value-adding detail. The one flaw is repetition: 'test mode only' appears in the title, the opening line, and again at the end, which is slightly wasteful.

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 zero parameters, a closed schema, and no output schema, the definition supplies everything an agent needs — the credential requirement, the error it will hit otherwise, what the values are, and how to apply them in simulate_transfer or payout creation.

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 the baseline is 4 and there is nothing for the description to disambiguate. It does clarify that the returned strings are recipient/sender account numbers, which is meaningful semantics even without a schema.

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 (list sandbox test values) plus a hard scope constraint (test mode only). Nothing among the ~80 siblings overlaps with it, and the agent can tell immediately this is the fixture-list tool rather than a live-data call.

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?

Explicitly says where the values plug in: as the recipient of a payout, or as `sender_account_number` when using simulate_transfer to test refunds. It also states the fallback behavior (any other number succeeds) and the precondition (sk_test_ key), so no inference is required.

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