Eve: gate the dangerous tool behind a human, in one field

The Stack

Tested Against

Prerequisites

• Node 20+
• An Eve project (npx eve@latest init) to actually run it

Steps

1. 1

   Author the gated tool and structure-check it

   Write agent.ts (names the model) and agent/tools/refund_payment.ts (a typed defineTool whose needsApproval predicate returns true above a threshold). CI runs a node check that the files are shaped right. The agent pausing for a human only happens on a live run, so that step is fenced.

   mkdir -p agent/tools
   cat > agent/agent.ts <<'TS'
   import { defineAgent } from "eve";
   
   export default defineAgent({
     model: "anthropic/claude-opus-4.8",
     name: "billing-assistant",
   });
   TS
   cat > agent/tools/refund_payment.ts <<'TS'
   import { defineTool } from "eve/tools";
   import { z } from "zod";
   import { processRefund } from "../lib/billing";
   
   export default defineTool({
     description: "Refund a payment to a customer by payment id.",
     inputSchema: z.object({
       paymentId: z.string(),
       amountUsd: z.number().positive(),
     }),
     needsApproval: ({ toolInput }) => toolInput.amountUsd >= 100,
     async execute({ paymentId, amountUsd }) {
       const result = await processRefund(paymentId, amountUsd);
       return { ok: result.ok, refundId: result.id };
     },
   });
   TS
   cat > lint.mjs <<'MJS'
   import { readFileSync } from "node:fs";
   const agent = readFileSync("agent/agent.ts", "utf8");
   const tool = readFileSync("agent/tools/refund_payment.ts", "utf8");
   function fail(m) { console.error("BAD: " + m); process.exit(1); }
   if (!agent.includes("defineAgent")) fail("agent.ts has no defineAgent");
   const mi = agent.indexOf("model:");
   if (mi < 0) fail("agent.ts declares no model");
   const mseg = agent.slice(mi, mi + 60);
   if (!mseg.includes(String.fromCharCode(34)) && !mseg.includes("'")) fail("model has no string value");
   if (!tool.includes("defineTool")) fail("refund_payment.ts has no defineTool");
   if (!tool.includes("inputSchema") || !tool.includes("z.object")) fail("tool has no Zod inputSchema");
   const ai = tool.indexOf("needsApproval");
   if (ai < 0) fail("tool has no needsApproval");
   if (!tool.slice(ai, ai + 80).includes("=>")) fail("needsApproval is not a function");
   console.log("config OK: agent.ts declares a model, refund_payment.ts exports a defineTool with a Zod inputSchema and a needsApproval function");
   MJS
   node lint.mjs

2. 2

   Run it and approve a refund (the live step, not checked by CI)

   Scaffold a real project with npx eve@latest init, run eve dev, and ask it to refund an amount over the threshold; the agent pauses at refund_payment and waits for your approval, then resumes. The model deciding and the tool firing are fenced.