Spend controls for Google ADK tools

Google ADK agents run tools through FunctionTool.execute. Paybond hooks that boundary — Harbor verifies spend before side effects and auto-submits evidence after success — not as model middleware.

Install @paybond/google-adk (npm) with @google/adk, or paybond-kit[google-adk] (pip). Adapter reference: /docs/kit/google-adk.

• Harbor verify before execute

  Wrapped FunctionTool handlers authorize operation and amount before paid work.

• Auto-evidence

  Guarded tools finalize spend and submit signed evidence after success.

• Policy budgets

  Versioned YAML caps per-call and intent spend for Gemini and GCP agents.

• TypeScript and Python

  Same google-adk adapter on npm (@paybond/google-adk) and pip (paybond-kit[google-adk]).

Why Paybond (not just ADK callbacks)?

ADK before_tool_callback and host confirmations do not enforce Harbor spend budgets, capability tokens, or signed completion evidence bound to an intent.

How it works

3-minute quickstart

Smoke the google-adk adapter Harbor contract — no Gemini credentials required for this check:

paybond login
paybond agent demo google-adk smoke \
  --operation paid-tool \
  --requested-spend-cents 100 \
  --evidence-preset cost_and_completion \
  --format table

paybond login
paybond agent demo google-adk smoke \
  --operation paid-tool \
  --requested-spend-cents 100 \
  --evidence-preset cost_and_completion \
  --format table

Install first:

# TypeScript
npm install @paybond/google-adk @google/adk
# Python
pip install "paybond-kit[google-adk]"

# TypeScript
npm install @paybond/google-adk @google/adk
# Python
pip install "paybond-kit[google-adk]"

When the smoke succeeds you should see:

• ✓ Spend approved
• ✓ Tool completed
• ✓ Evidence verified (cost_and_completion)

What success looks like

Scaffold

# TypeScript
paybond init agent-middleware --framework google-adk --out paybond-google-adk.ts
# Python
paybond init agent-middleware --framework google-adk --out paybond_google_adk.py
paybond policy init --preset saas --out paybond.policy.yaml

# TypeScript
paybond init agent-middleware --framework google-adk --out paybond-google-adk.ts
# Python
paybond init agent-middleware --framework google-adk --out paybond_google_adk.py
paybond policy init --preset saas --out paybond.policy.yaml

Validate before deploy:

paybond policy validate-tools --file paybond.policy.yaml --local-only

paybond policy validate-tools --file paybond.policy.yaml --local-only

Wire middleware

import { FunctionTool, LlmAgent } from "@google/adk";
import { Paybond } from "@paybond/kit";

const paybond = await Paybond.open({ apiKey: process.env.PAYBOND_API_KEY! });

const bookHotelTool = new FunctionTool({
  name: "travel.book_hotel",
  description: "Book a hotel room",
  parameters: {
    type: "object",
    properties: {
      city: { type: "string" },
      estimatedPriceCents: { type: "integer", minimum: 0 },
    },
    required: ["city", "estimatedPriceCents"],
  },
  execute: async (args) => bookHotel(args),
});

const { agentTools: tools } = await paybond.agent({
  policy: "saas",
  framework: "google-adk",
  tools: [bookHotelTool, searchWebTool],
});

const agent = new LlmAgent({ name: "Travel", tools });

import { FunctionTool, LlmAgent } from "@google/adk";
import { Paybond } from "@paybond/kit";

const paybond = await Paybond.open({ apiKey: process.env.PAYBOND_API_KEY! });

const bookHotelTool = new FunctionTool({
  name: "travel.book_hotel",
  description: "Book a hotel room",
  parameters: {
    type: "object",
    properties: {
      city: { type: "string" },
      estimatedPriceCents: { type: "integer", minimum: 0 },
    },
    required: ["city", "estimatedPriceCents"],
  },
  execute: async (args) => bookHotel(args),
});

const { agentTools: tools } = await paybond.agent({
  policy: "saas",
  framework: "google-adk",
  tools: [bookHotelTool, searchWebTool],
});

const agent = new LlmAgent({ name: "Travel", tools });

Manual hook wiring

When you already bound a PaybondAgentRun:

import { createPaybondGoogleAdkConfig } from "@paybond/google-adk";

const config = createPaybondGoogleAdkConfig(run, sdkTools);
const guardedTools = config.tools;

import { createPaybondGoogleAdkConfig } from "@paybond/google-adk";

const config = createPaybondGoogleAdkConfig(run, sdkTools);
const guardedTools = config.tools;

Approval holds: when Harbor returns an approval hold, Python guarded tools raise RuntimeError with a Paybond message; TypeScript rethrows a clear Error (Paybond capability approval required: …) with the Harbor error as cause. Approve in the tenant console, store the approval token on the run with the ADK functionCallId, then retry with the same operation, amount, metadata, and approvalToken. Hard denials must not execute the tool.

Bypass classes: GOOGLE_SEARCH and ADK built-ins, unwrapped tools, AgentTool / RemoteA2aAgent remote hops, and before_tool_callback-only checks are not governed.

Production: omit sandbox defaults on paybond.agent() / paybond.instrument(), use deferred bind, then instrumented.bind({ intentId, capabilityToken }) per session. Tenant and intent IDs come from the Paybond session binding — never from unauthenticated tool args.

Production checklist

Works with

Ready to test?

Related guides

• Agent middleware — bind, registry, tenant isolation
• Agent-agnostic spend controls — raw Gemini SDK function calling
• Agent policy-as-code — versioned YAML
• OpenAI Agents spend controls — similar FunctionTool boundary pattern

Developer reference: /docs/kit/google-adk.