@fidacy/langchain

@fidacy/langchain

Gate LangChain tool calls behind a signed Fidacy verdict. A denied payment never executes.

npm i @fidacy/langchain @langchain/core

import { guardTools } from "@fidacy/langchain";

const tools = guardTools([payTool, searchTool], { apiKey: process.env.FIDACY_ENGINE_API_KEY });
// payTool is now assessed before every call. searchTool is returned untouched.

Free engine key, no card: https://fidacy.com/claim

Why not a callback handler

LangChain callbacks (handleToolStart and friends) are observational. They fire around the call and cannot cancel it, so a guardrail built on them watches the money leave. This replaces the tool's own execution path, which is the only place that can actually stop a payment.

Fail-closed

If the engine is unreachable, the key is wrong, or the request times out, the call is denied. A payment firewall that opens when it breaks is not a firewall.

review also blocks by default. Set reviewIsDeny: false to let it through.

What a denial looks like

guardTool throws FidacyDenied with the signed proof attached:

try {
  await tools[0].invoke({ payee: "acme", amount: 5000 });
} catch (e) {
  if (e instanceof FidacyDenied) {
    e.decision;                // "deny" | "review" | "unavailable"
    e.verdict?.riskPayloadJws; // detached JWS, verify offline with @fidacy/verify
    e.verdict?.assessmentId;
  }
}

Options

Option	Default	What it does
apiKey	FIDACY_ENGINE_API_KEY	Engine credential
engineUrl	https://api.fidacy.com	Engine base URL
client	built from apiKey	Bring your own @fidacy/sdk client
isPayment	name heuristic	Which tools guardTools gates
toMandate	payee/amount/currency + raw args	Build the mandate the engine assesses
reviewIsDeny	true	Whether review blocks
onDecision	none	Observe every decision, including approvals

guardTool(tool, opts) gates one tool unconditionally. guardTools(list, opts) gates only the ones isPayment matches and returns the rest by identity, so non-payment tools carry no cost.

The wrapped tool keeps its name, description and schema, so the model sees no difference.

Apache-2.0 · https://fidacy.com