Tests an AI agent's purchase against the task it was given. Paid per call in USDC via x402.
Scored across 2 tools
safe4_authorize and safe4_price are largely distinct: one provides pricing and the other renders an authorization decision. Minor overlap exists because authorize can return a price list when called without payment, but the descriptions clearly explain this behavior.
Both tools share the safe4_ prefix and use consistent snake_case naming. The only inconsistency is that authorize is an imperative verb while price is a noun rather than get_price, but the set still reads coherently.
Two tools is on the low end but appropriate for this narrow service: a free price quote and a paid authorization decision. Each tool serves a necessary step in the workflow, though the set is slightly thinner than typical.
The core workflow is covered: discover price, then authorize with an x402 payment payload. There is no audit-lookup or cancellation tool, but agents can complete the primary task without those operations.
Decide whether a proposed agent payment should proceed.
Settled per call in USDC over x402. Called without payment it
returns the price list rather than a decision; call it again with the
signed payload to receive one.
The task and the two allow-lists are the principal's constraints, not
the agent's: they are what the purchase is tested against, so an agent
that writes its own task is grading its own homework. Safe4 records
every field it was given in the audit entry and marks the task context
as request-supplied, so a substituted constraint is visible afterwards.
Args: task: The task the agent was given, as stated by its principal. purchase: What is being bought. purchase_purpose: Why this purchase serves the task. amount: Decimal amount as a string, for example "25.00". currency: Currency of the proposed payment, for example "USDC". counterparty: Who would receive the payment. service_category: Category of the thing being bought. allowed_service_categories: Categories the principal permits. allowed_counterparties: Optional payees the principal permits. When supplied, payment to anyone else is denied. task_id: Optional caller-side task identifier, echoed into the audit. payment: An x402 payment payload for this call. Omit to receive the price list instead of a decision.
| Name | Required | Description | Default |
|---|---|---|---|
| task | Yes | ||
| amount | Yes | ||
| payment | No | ||
| task_id | No | ||
| currency | Yes | ||
| purchase | Yes | ||
| counterparty | Yes | ||
| purchase_purpose | Yes | ||
| service_category | Yes | ||
| allowed_counterparties | No | ||
| allowed_service_categories | Yes |
| Name | Required | Description |
|---|---|---|
No output parameters | ||
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description carries the full transparency burden. It discloses payment and settlement ('Settled per call in USDC over x402'), the two-phase call behavior, and the audit trail behavior ('records every field it was given... substituted constraint is visible afterwards'). This is rich behavioral disclosure beyond a bare action verb.
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 description opens with a one-line purpose, front-loads the most critical behavior, and then uses a clearly labeled Args block. The prose paragraphs about constraints and audit are substantial but each adds behavioral context; nothing reads as 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?
The description covers the two call modes, payment/settlement, principal-vs-agent constraints, and audit behavior. With an output schema present, the absence of detailed return-value documentation is not a gap; an agent has enough information to invoke the tool correctly and understand its consequences.
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 0%, and the description compensates by glossing all 11 parameters. It adds operational meaning such as amount as a decimal string ('25.00'), currency example 'USDC', and allowed_counterparties behavior ('When supplied, payment to anyone else is denied').
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 the action and resource explicitly: 'Decide whether a proposed agent payment should proceed.' It also distinguishes itself from the sibling by noting that omitting payment returns the price list instead of a decision, so an agent can separate it from safe4_price.
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 direct invocation guidance: call without `payment` to receive the price list, then call again with the signed payload to get a decision. It does not name safe4_price as the alternative, but the price-list behavior effectively draws the boundary and no misleading usage conditions are present.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Price and accepted payment networks for one Safe4 decision.
Free to call. Returns the same x402 terms the HTTP endpoint advertises, so an agent can see the cost before committing to a paid call.
| Name | Required | Description | Default |
|---|---|---|---|
No parameters | |||
| Name | Required | Description |
|---|---|---|
No output parameters | ||
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the burden and does well: it discloses that the call is free, non-committal, and returns the same x402 terms as the HTTP endpoint. This tells the agent this is a read-only/quote operation with no payment side effect. It does not mention rate limits or response shape, but the output schema exists to cover return structure.
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 short sentences, each earning its place: what the tool returns, that it is free, and why an agent should call it. The core purpose is front-loaded, and there is no redundant repetition of the name or title.
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?
For a zero-parameter, output-schema-backed price quote tool, the description is complete. An agent knows what it will get, that it costs nothing, and how to use it in the flow relative to the paid authorization step. Nothing else is needed to invoke it correctly.
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?
There are zero parameters and schema coverage is 100%, so the description has no parameter burden to carry. The baseline for zero-parameter tools is 4, and the description adds relevant context about what the returned terms represent without needing to explain inputs.
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?
Description states a specific verb-resource pair: it tells the agent it returns the price and accepted payment networks for a Safe4 decision. It also distinguishes itself from the paid/authorize path by positioning itself as the pre-commitment cost check, so an agent knows this is the quoting sibling, not the authorization tool.
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 clearly says when to use it: before committing to a paid call, with the added reassurance that it is free to call. It implies the alternative is the paid/authorize flow but does not name the sibling explicitly or give explicit 'use this instead of X' language, so it stops just short of full routing guidance.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Recent tool additions, removals, and schema changes observed during successful MCP inspections.
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