@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";

// No key, no signup: the offline judge decides your first 20 calls.
const tools = guardTools([payTool, searchTool]);
// payTool is now assessed before every call. searchTool is returned untouched.

Two ways it decides

Offline, out of the box. With no credential the deterministic local judge runs: deny-by-default, your own limits, a hash-chained log on your machine. The first 20 decisions on an install are free and need no account, so you can watch a payment get blocked before deciding whether you want any of this.

Set the limits that fit your case:

const tools = guardTools([payTool], {
  mandate: { payees: ["acme-inc"], perTxMax: 5_000, maxTotal: 50_000 },
});

A blocked call tells you what was stopped, in money terms, and prints the exact edit that would allow it.

Hosted, with an account. Pass apiKey and the engine decides instead, returning a verdict signed with a stable key that anyone can verify against the public JWKS, plus a Bitcoin-anchored audit chain that outlives your process.

Free 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. Omit it to stay offline
mandate	none	Offline limits: payees, perTxMax, maxTotal, currency
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