diff --git a/README.md b/README.md
index 824427a..360a35e 100644
--- a/README.md
+++ b/README.md
@@ -4,3 +4,24 @@ This is a template project with best-practice modules:
 - Winterspec for defining the API
 - bun testing
 - Zustand store with zod definition for database state
+
+## Fake payments API
+
+The project includes a small in-memory payment API suitable for fake bounty/payment flows:
+
+- `POST /payments/send` — create a pending fake payment. Supports `idempotency_key` so retries return the original payment.
+- `GET /payments/list` — list payments, optionally filtered by `status` or `bounty_id`.
+- `GET /payments/get?payment_id=...` — fetch a single payment.
+- `POST /payments/update-status` — update a payment to `pending`, `completed`, `cancelled`, or `failed`.
+
+Example send body:
+
+```json
+{
+  "recipient": "maintainer@example.com",
+  "amount": 10,
+  "currency": "USD",
+  "bounty_id": "tscircuit/fake-algora#1",
+  "idempotency_key": "bounty-1-payment"
+}
+```
diff --git a/bun.lockb b/bun.lockb
index 557d79c..7e3c28a 100755
Binary files a/bun.lockb and b/bun.lockb differ
diff --git a/lib/db/db-client.ts b/lib/db/db-client.ts
index e525e65..dad62c1 100644
--- a/lib/db/db-client.ts
+++ b/lib/db/db-client.ts
@@ -1,8 +1,12 @@
-import { createStore, type StoreApi } from "zustand/vanilla"
-import { immer } from "zustand/middleware/immer"
-import { hoist, type HoistedStoreApi } from "zustand-hoist"
+import { createStore } from "zustand/vanilla"
+import { hoist } from "zustand-hoist"
 
-import { databaseSchema, type DatabaseSchema, type Thing } from "./schema.ts"
+import {
+  databaseSchema,
+  type Payment,
+  type PaymentStatus,
+  type Thing,
+} from "./schema.ts"
 import { combine } from "zustand/middleware"
 
 export const createDatabase = () => {
@@ -11,7 +15,9 @@ export const createDatabase = () => {
 
 export type DbClient = ReturnType<typeof createDatabase>
 
-const initializer = combine(databaseSchema.parse({}), (set) => ({
+const nowIso = () => new Date().toISOString()
+
+const initializer = combine(databaseSchema.parse({}), (set, get) => ({
   addThing: (thing: Omit<Thing, "thing_id">) => {
     set((state) => ({
       things: [
@@ -21,4 +27,49 @@ const initializer = combine(databaseSchema.parse({}), (set) => ({
       idCounter: state.idCounter + 1,
     }))
   },
+
+  createPayment: (
+    payment: Omit<
+      Payment,
+      "payment_id" | "status" | "created_at" | "updated_at"
+    >,
+  ) => {
+    const existing = payment.idempotency_key
+      ? get().payments.find((p) => p.idempotency_key === payment.idempotency_key)
+      : undefined
+
+    if (existing) return existing
+
+    const timestamp = nowIso()
+    const newPayment: Payment = {
+      ...payment,
+      payment_id: get().paymentIdCounter.toString(),
+      status: "pending",
+      created_at: timestamp,
+      updated_at: timestamp,
+    }
+
+    set((state) => ({
+      payments: [...state.payments, newPayment],
+      paymentIdCounter: state.paymentIdCounter + 1,
+    }))
+
+    return newPayment
+  },
+
+  updatePaymentStatus: (paymentId: string, status: PaymentStatus) => {
+    let updatedPayment: Payment | undefined
+    set((state) => ({
+      payments: state.payments.map((payment) => {
+        if (payment.payment_id !== paymentId) return payment
+        updatedPayment = {
+          ...payment,
+          status,
+          updated_at: nowIso(),
+        }
+        return updatedPayment
+      }),
+    }))
+    return updatedPayment
+  },
 }))
diff --git a/lib/db/schema.ts b/lib/db/schema.ts
index 8377516..73ca4e1 100644
--- a/lib/db/schema.ts
+++ b/lib/db/schema.ts
@@ -9,8 +9,32 @@ export const thingSchema = z.object({
 })
 export type Thing = z.infer<typeof thingSchema>
 
+export const paymentStatusSchema = z.enum([
+  "pending",
+  "completed",
+  "cancelled",
+  "failed",
+])
+export type PaymentStatus = z.infer<typeof paymentStatusSchema>
+
+export const paymentSchema = z.object({
+  payment_id: z.string(),
+  recipient: z.string(),
+  amount: z.number().positive(),
+  currency: z.string().min(1),
+  memo: z.string().optional(),
+  bounty_id: z.string().optional(),
+  idempotency_key: z.string().optional(),
+  status: paymentStatusSchema,
+  created_at: z.string(),
+  updated_at: z.string(),
+})
+export type Payment = z.infer<typeof paymentSchema>
+
 export const databaseSchema = z.object({
   idCounter: z.number().default(0),
+  paymentIdCounter: z.number().default(0),
   things: z.array(thingSchema).default([]),
+  payments: z.array(paymentSchema).default([]),
 })
 export type DatabaseSchema = z.infer<typeof databaseSchema>
diff --git a/routes/payments/get.ts b/routes/payments/get.ts
new file mode 100644
index 0000000..8219606
--- /dev/null
+++ b/routes/payments/get.ts
@@ -0,0 +1,20 @@
+import { z } from "zod"
+import { paymentSchema } from "lib/db/schema"
+import { withRouteSpec } from "lib/middleware/with-winter-spec"
+
+export default withRouteSpec({
+  methods: ["GET"],
+  queryParams: z.object({
+    payment_id: z.string(),
+  }),
+  jsonResponse: z.object({
+    payment: paymentSchema.nullable(),
+  }),
+})((req, ctx) => {
+  const url = new URL(req.url)
+  const paymentId = url.searchParams.get("payment_id")
+  const payment =
+    ctx.db.payments.find((p) => p.payment_id === paymentId) ?? null
+
+  return ctx.json({ payment })
+})
diff --git a/routes/payments/list.ts b/routes/payments/list.ts
new file mode 100644
index 0000000..a01414e
--- /dev/null
+++ b/routes/payments/list.ts
@@ -0,0 +1,25 @@
+import { z } from "zod"
+import { paymentSchema, paymentStatusSchema } from "lib/db/schema"
+import { withRouteSpec } from "lib/middleware/with-winter-spec"
+
+export default withRouteSpec({
+  methods: ["GET"],
+  queryParams: z.object({
+    status: paymentStatusSchema.optional(),
+    bounty_id: z.string().optional(),
+  }),
+  jsonResponse: z.object({
+    payments: z.array(paymentSchema),
+  }),
+})((req, ctx) => {
+  const url = new URL(req.url)
+  const status = url.searchParams.get("status")
+  const bountyId = url.searchParams.get("bounty_id")
+  const payments = ctx.db.payments.filter((payment) => {
+    if (status && payment.status !== status) return false
+    if (bountyId && payment.bounty_id !== bountyId) return false
+    return true
+  })
+
+  return ctx.json({ payments })
+})
diff --git a/routes/payments/send.ts b/routes/payments/send.ts
new file mode 100644
index 0000000..32d1f41
--- /dev/null
+++ b/routes/payments/send.ts
@@ -0,0 +1,30 @@
+import { z } from "zod"
+import { paymentSchema } from "lib/db/schema"
+import { withRouteSpec } from "lib/middleware/with-winter-spec"
+
+export const sendPaymentBodySchema = z.object({
+  recipient: z.string().min(1),
+  amount: z.number().positive(),
+  currency: z.string().min(1).default("USD"),
+  memo: z.string().optional(),
+  bounty_id: z.string().optional(),
+  idempotency_key: z.string().optional(),
+})
+
+export default withRouteSpec({
+  methods: ["POST"],
+  jsonBody: sendPaymentBodySchema,
+  jsonResponse: z.object({
+    payment: paymentSchema,
+    idempotent: z.boolean(),
+  }),
+})(async (req, ctx) => {
+  const body = await req.json()
+  const beforeCount = ctx.db.payments.length
+  const payment = ctx.db.createPayment(body)
+
+  return ctx.json({
+    payment,
+    idempotent: ctx.db.payments.length === beforeCount,
+  })
+})
diff --git a/routes/payments/update-status.ts b/routes/payments/update-status.ts
new file mode 100644
index 0000000..157be83
--- /dev/null
+++ b/routes/payments/update-status.ts
@@ -0,0 +1,19 @@
+import { z } from "zod"
+import { paymentSchema, paymentStatusSchema } from "lib/db/schema"
+import { withRouteSpec } from "lib/middleware/with-winter-spec"
+
+export default withRouteSpec({
+  methods: ["POST"],
+  jsonBody: z.object({
+    payment_id: z.string(),
+    status: paymentStatusSchema,
+  }),
+  jsonResponse: z.object({
+    payment: paymentSchema.nullable(),
+  }),
+})(async (req, ctx) => {
+  const { payment_id, status } = await req.json()
+  const payment = ctx.db.updatePaymentStatus(payment_id, status) ?? null
+
+  return ctx.json({ payment })
+})
diff --git a/tests/routes/payments/send.test.ts b/tests/routes/payments/send.test.ts
new file mode 100644
index 0000000..88a8334
--- /dev/null
+++ b/tests/routes/payments/send.test.ts
@@ -0,0 +1,41 @@
+import { expect, test } from "bun:test"
+import { getTestServer } from "tests/fixtures/get-test-server"
+
+test("send, list, get, and update fake payments", async () => {
+  const { axios } = await getTestServer()
+
+  const first = await axios.post("/payments/send", {
+    recipient: "maintainer@example.com",
+    amount: 10,
+    currency: "USD",
+    bounty_id: "tscircuit/fake-algora#1",
+    idempotency_key: "bounty-1-payment",
+  })
+
+  expect(first.data.payment.payment_id).toBe("0")
+  expect(first.data.payment.status).toBe("pending")
+  expect(first.data.idempotent).toBe(false)
+
+  const retry = await axios.post("/payments/send", {
+    recipient: "maintainer@example.com",
+    amount: 10,
+    currency: "USD",
+    bounty_id: "tscircuit/fake-algora#1",
+    idempotency_key: "bounty-1-payment",
+  })
+
+  expect(retry.data.payment.payment_id).toBe(first.data.payment.payment_id)
+  expect(retry.data.idempotent).toBe(true)
+
+  const list = await axios.get("/payments/list?status=pending")
+  expect(list.data.payments).toHaveLength(1)
+
+  const get = await axios.get("/payments/get?payment_id=0")
+  expect(get.data.payment.recipient).toBe("maintainer@example.com")
+
+  const updated = await axios.post("/payments/update-status", {
+    payment_id: "0",
+    status: "completed",
+  })
+  expect(updated.data.payment.status).toBe("completed")
+})