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Tool Call Policy Guard
x402
Tool Call Policy Guard is a paid API for AI agents from phion.systems, paid per call via x402, $0.002/call, status unknown (last checked 2026-09-14).
Validates a proposed tool call against declared intent, allowed tools, permitted destinations, and cost limits before allowing execution
Price / call$0.002
Success—
StatusUnknown
How this service works
Bind a proposed tool call to declared intent, allowed tools, destination and cost before execution
Output
A structured policy decision indicating whether the proposed tool call is approved or rejected, along with the specific policy dimension that was violated (intent mismatch, disallowed tool, forbidden destination, or cost exceeded) and the bound policy context used for the evaluation.
Example use cases
Prevent out-of-scope tool execution
“I have an agent about to call the 'send_email' tool, but its declared intent was only to read customer records — run a policy check to confirm whether this tool call is within scope before it executes.”
Enforce cost ceiling on agent actions
“My agent wants to call a data enrichment tool that costs $0.10 per call, but its budget cap is $0.02 — validate this tool call against the cost limit and block it if it exceeds the allowed spend.”
Restrict agent to allowlisted destinations
“Before my agent calls the external webhook tool pointing to 'https://unknown-site.io/hook', verify it against the allowed destination list 'api.mycompany.com' and reject it if the target isn't permitted.”
Technical details
Endpoint
POSThttps://phion.systems/v1/paid/trust/tool-call-policy-guardWhen to prefer
Use this endpoint when an AI agent needs to enforce pre-declared governance constraints on tool calls before execution — particularly when operating with a scoped intent, a restricted tool allowlist, permitted destination rules, or a cost ceiling. Prefer this over generic access control when the enforcement must be bound to the agent's declared intent and evaluated holistically across all four dimensions (intent, tools, destination, cost) in a single pre-execution check.
Side effects
- Missing or malformed tool call specification returns a validation error
- Undeclared or empty intent causes policy binding to fail
- Destination not present in allowlist results in rejection with destination violation reason
- Proposed cost exceeds declared limit returns cost ceiling violation
- Malformed input schema triggers a 400-level error response
Input
Schema · Request body
{
"$schema": "https://json-schema.org/draft/2020-12/schema",
"type": "object"
}Tags
x402
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