@aegis-sdk/langchain

@aegis-sdk/langchain

LangChain.js callback handler and chain guard for prompt injection defense.

Part of the Aegis.js prompt injection defense toolkit.

Installation

npm install @aegis-sdk/langchain @aegis-sdk/core

Quick Start

import { ChatOpenAI } from '@langchain/openai';
import { Aegis } from '@aegis-sdk/core';
import { createAegisCallback } from '@aegis-sdk/langchain';

const aegis = new Aegis({ policy: 'strict' });

const model = new ChatOpenAI({
  callbacks: [createAegisCallback(aegis)],
});

const result = await model.invoke('Hello!');

API

createAegisCallback(optionsOrAegis?)

Creates a LangChain-compatible callback handler that intercepts LLM and tool lifecycle events:

• handleLLMStart -- Scans input prompts for injection patterns
• handleLLMEnd -- Quarantines LLM output for safe downstream consumption
• handleToolStart -- Validates tool calls against the Aegis policy
• handleToolEnd -- Quarantines tool output

Accepts an Aegis instance, AegisConfig, or AegisCallbackOptions:

Option	Type	Default	Description
aegis	AegisConfig | Aegis	{}	Aegis configuration or pre-constructed instance
scanInput	boolean	true	Scan LLM input prompts
scanOutput	boolean	true	Scan LLM output for violations
validateTools	boolean	true	Validate tool calls against policy
quarantineToolOutput	boolean	true	Quarantine tool outputs
onBlocked	(error) => void	--	Called when input is blocked
onToolBlocked	(toolName, result) => void	--	Called when a tool call is blocked

AegisChainGuard

Wraps agentic chain/agent execution with step-level protection. Enforces a step budget, tracks cumulative risk across steps, and terminates the chain if risk exceeds the threshold.

import { AegisChainGuard } from '@aegis-sdk/langchain';

const guard = new AegisChainGuard({
  aegis: new Aegis({ policy: 'strict' }),
  maxSteps: 10,
  riskThreshold: 0.7,
});

// In your agent loop:
const result = await guard.guardChainStep(currentMessages);
if (!result.allowed) {
  console.error('Chain terminated:', result.reason);
  break;
}

Option	Type	Default	Description
aegis	AegisConfig | Aegis	{}	Aegis configuration or pre-constructed instance
maxSteps	number	25	Maximum chain steps before termination
riskThreshold	number	0.8	Cumulative risk score threshold (0-1)
scanStrategy	ScanStrategy	"last-user"	Which messages to scan per step
onBudgetExceeded	(stepCount) => void	--	Called when step budget is exceeded
onRiskExceeded	(cumulativeRisk) => void	--	Called when risk threshold is exceeded

Methods: guardChainStep(messages), getStepCount(), getCumulativeRisk(), getAegisInstance(), reset().

guardMessages(aegis, messages, options?)

Scans messages directly without using the callback handler. Throws AegisInputBlocked if input is blocked.

Re-exports

Aegis, AegisInputBlocked, AegisSessionQuarantined, AegisSessionTerminated, and all core types (including ActionValidationRequest, ActionValidationResult) are re-exported for convenience.

Learn More

• Documentation
• GitHub

License

MIT