LangGraph Integration
Use Veto with LangGraph JS ToolNode by wrapping executable tools before graph execution.
Veto works with LangGraph JS by wrapping executable LangChain-style tools before passing them to a ToolNode.
The current local TypeScript SDK supports objects that expose func, invoke, execute, or handler. It does not ship a dedicated createVetoToolNode helper or a Python LangGraph package in this repository.
Installation
npm install veto-sdk @langchain/core @langchain/langgraphQuick start
import { ToolNode } from "@langchain/langgraph/prebuilt";
import { Veto, ToolCallDeniedError } from "veto-sdk";
const veto = await Veto.init();
const tools = [
{
name: "transfer_funds",
description: "Transfer money between accounts",
func: async (input: { amount: number; to_account: string }) => {
return `Transferred $${input.amount} to ${input.to_account}`;
},
invoke: async function (input: { amount: number; to_account: string }) {
return this.func(input);
},
},
];
const safeTools = veto.wrap(tools, {
context: {
agentId: "langgraph-agent",
sessionId: "support-session",
},
});
const toolNode = new ToolNode(safeTools);When the graph calls invoke, Veto validates the tool name and arguments through /v1/validate before the original tool runs.
Denial handling
try {
await safeTools[0].invoke({ amount: 5000, to_account: "external" });
} catch (error) {
if (error instanceof ToolCallDeniedError) {
console.log(`Blocked by Veto: ${error.reason ?? error.decision}`);
} else {
throw error;
}
}Register tools for Charter
Register the same tools so Charter can draft policy against the actual graph surface:
await veto.registerTools([
{
name: "transfer_funds",
description: "Transfer money between accounts",
parameters: [
{ name: "amount", type: "number", required: true },
{ name: "to_account", type: "string", required: true },
],
},
]);
const res = await fetch("https://api.veto.so/v1/charter/turn", {
method: "POST",
headers: {
"Content-Type": "application/json",
"X-Veto-API-Key": process.env.VETO_API_KEY!,
},
body: JSON.stringify({
message: "Transfers over $1,000 require finance approval.",
mode: "compile",
surface: "api",
}),
});
const draft = await res.json();
console.log(draft.verification.linkUrl);Policy-changing Charter results require verification before anything goes live.