Verifiable random bytes for a draw, raffle or tie-break: an ECVRF output over your seed plus a proof anyone can check offline. The same seed always gives the same output, so publish the seed first to show the result was not picked. Costs $0.006 per call. The first 5 priced calls per caller are free.
| Name | Required | Description | Default |
|---|---|---|---|
| seed | Yes | Seed or message the draw is bound to. | |
| num_bytes | No | Output length (default 32). |
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden of behavioral disclosure. It does well by revealing determinism ('same seed always gives the same output'), verifiability, the proof mechanism, pricing ($0.006 per call), and the free tier. It does not specify the exact response structure, but the core behavior is transparent.
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?
Three sentences, each earning its place: purpose and mechanism, determinism/fairness guidance, and pricing. The most important information is front-loaded, and there is no redundant or filler content.
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?
Despite having no output schema and no annotations, the description covers purpose, behavior, determinism, verification, and cost, which is enough for an agent to invoke the tool correctly. It could briefly mention the returned proof format, but the current level of detail is strong for a tool of this simplicity.
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 description coverage is 100%, so the baseline is 3. The description adds meaningful context for 'seed' by explaining determinism and the need to publish it first, but it does not add new meaning for 'num_bytes' beyond the schema's default and range. This matches the baseline expectation.
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 description states a specific purpose: producing verifiable random bytes for draws, raffles, or tie-breaks, via an ECVRF output with a checkable proof. It clearly differentiates from the unrelated siblings (air quality, market, weather tools) and explains the core function without ambiguity.
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 gives clear use cases ('for a draw, raffle or tie-break') and explains the important usage pattern of publishing the seed first to prove fairness. It does not explicitly name alternatives or exclusion criteria, but the sibling tools are unrelated, so this is sufficient context.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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