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

With zero annotations, the description carries the full burden and delivers comprehensively: it discloses write scope ('it adds test credits and nothing else'), the auth prerequisite (agent identity plus bearer token), rate-limit behavior (429 with exact retry second), the streak-reset rule, and the non-convertible, non-purchasable nature of credits. This exceeds what annotations would typically provide.

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?

The core purpose is front-loaded and most sentences carry real content, but several are redundant or purely stylistic - 'A slow day rather than a dead one' restates 'Every face pays something,' and 'What matters to a program is not the thrill but the arithmetic' is a flourish that adds no fact. At roughly 200 words for a tool with one optional parameter, it is verbose enough to cost the agent parsing time.

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 and no annotations, the description must explain behavior, return content, and side effects on its own - and it covers purpose, payout floor, streak mechanics, retry timing, currency semantics, auth, and the fact that every reply carries the full odds table. An agent can invoke this tool correctly using only this text.

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 single parameter is already documented at 100% by the schema (spin vs status, with default), so the baseline is 3. The description adds decision framing around the response table but no new parameter-level semantics beyond what the schema already states.

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?

The opening sentence names a specific verb+resource combination ('Spin once per window for free sandbox credits') with a cadence attached. This is clearly differentiated from all 17 siblings - it is the only daily-reward/credit-granting mechanic, and later detail (credits buy practice purchases and measurement-queue places) pins down its exact scope.

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?

The description tells the agent when this call is worth making ('decide once whether this call earns its place in your loop'), warns against double-calling ('Calling it twice inside the window is refused with 429'), and pairs with the schema's status action for checking without spinning. It never names an alternative tool for earning credits, which keeps it just short of a 5.

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