diff --git a/README.md b/README.md
index e9c3a88..4c66a50 100644
--- a/README.md
+++ b/README.md
@@ -63,7 +63,13 @@ normalizing keys postfixed with brackets, the brackets are removed and the value
 of all keys with the same name, are joined into one array in the order they
 appear.
 
-The adapter has no options.
+Available options:
+- `setStructureInKeys`: When this is `true`, we'll serialize key and values so
+  that the structure of value is set in the key, with the leaf values as
+  values. `{ data: [{ id: 'ent1 }] }` will for instance be serialized to the
+  key `data[0][id]` and the value `'ent1'`. Default behavior (or when
+  `setStructureInKeys` is `false`) is to use the first level as key (`data` in
+  this case, and JSON stringify the rest as value.
 
 ### Form transformer
 
diff --git a/src/index.test.ts b/src/index.test.ts
index 3ca0cf7..768f05e 100644
--- a/src/index.test.ts
+++ b/src/index.test.ts
@@ -19,9 +19,19 @@ test('should be an Integreat adapter', () => {
 // Tests -- prepareOptions
 
 test('should prepare options', () => {
+  const options = { setStructureInKeys: true }
+  const serviceId = 'entries'
+  const expected = { setStructureInKeys: true }
+
+  const ret = adapter.prepareOptions(options, serviceId)
+
+  assert.deepEqual(ret, expected)
+})
+
+test('should remove unknown options', () => {
   const options = { dontKnow: 'whatthisis' }
   const serviceId = 'entries'
-  const expected = {}
+  const expected = { setStructureInKeys: false }
 
   const ret = adapter.prepareOptions(options, serviceId)
 
@@ -81,6 +91,35 @@ test('should normalize response data', async () => {
   assert.deepEqual(ret, expected)
 })
 
+test('should normalize form data serialized with setStructureInKeys', async () => {
+  const options = { setStructureInKeys: true } // We normalize this kind of data regardless of this flag, but it will often be set in these cases
+  const action = {
+    type: 'SET',
+    payload: {
+      type: 'entry',
+      data: 'items[0][value]=1&items[0][text]=Several+words+here&items[1][value]=2&items[1][text]=More+words+here',
+    },
+    meta: { ident: { id: 'johnf' } },
+  }
+  const expected = {
+    type: 'SET',
+    payload: {
+      type: 'entry',
+      data: {
+        items: [
+          { value: 1, text: 'Several words here' },
+          { value: 2, text: 'More words here' },
+        ],
+      },
+    },
+    meta: { ident: { id: 'johnf' } },
+  }
+
+  const ret = await adapter.normalize(action, options)
+
+  assert.deepEqual(ret, expected)
+})
+
 // Tests -- serialize
 
 test('should serialize payload', async () => {
@@ -155,3 +194,32 @@ test('should serialize first item when data is an array', async () => {
 
   assert.deepEqual(ret, expected)
 })
+
+test('should serialize when setStructureInKeys is true', async () => {
+  const options = { setStructureInKeys: true }
+  const action = {
+    type: 'SET',
+    payload: {
+      type: 'entry',
+      data: {
+        items: [
+          { value: 1, text: 'Several words here' },
+          { value: 2, text: 'More words here' },
+        ],
+      },
+    },
+    meta: { ident: { id: 'johnf' } },
+  }
+  const expected = {
+    type: 'SET',
+    payload: {
+      type: 'entry',
+      data: 'items[0][value]=1&items[0][text]=Several+words+here&items[1][value]=2&items[1][text]=More+words+here',
+    },
+    meta: { ident: { id: 'johnf' } },
+  }
+
+  const ret = await adapter.serialize(action, options)
+
+  assert.deepEqual(ret, expected)
+})
diff --git a/src/index.ts b/src/index.ts
index ead83e3..15f549e 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -2,6 +2,10 @@ import parseFormData from './utils/parseFormData.js'
 import stringifyFormData from './utils/stringifyFormData.js'
 import type { Action, Adapter } from 'integreat'
 
+export interface Options extends Record<string, unknown> {
+  setStructureInKeys?: boolean
+}
+
 const firstIfArray = (data: unknown) => (Array.isArray(data) ? data[0] : data)
 
 const setActionData = (
@@ -23,20 +27,26 @@ const setActionData = (
 })
 
 const adapter: Adapter = {
-  prepareOptions(_options, _serviceId) {
-    return {}
+  prepareOptions({ setStructureInKeys = false }: Options, _serviceId) {
+    return { setStructureInKeys }
   },
 
-  async normalize(action, _options) {
+  async normalize(action, _options: Options) {
     const payloadData = parseFormData(action.payload.data)
     const responseData = parseFormData(action.response?.data)
 
     return setActionData(action, payloadData, responseData)
   },
 
-  async serialize(action, _options) {
-    const payloadData = stringifyFormData(firstIfArray(action.payload.data))
-    const responseData = stringifyFormData(firstIfArray(action.response?.data))
+  async serialize(action, { setStructureInKeys }: Options) {
+    const payloadData = stringifyFormData(
+      firstIfArray(action.payload.data),
+      setStructureInKeys,
+    )
+    const responseData = stringifyFormData(
+      firstIfArray(action.response?.data),
+      setStructureInKeys,
+    )
 
     return setActionData(action, payloadData, responseData)
   },
diff --git a/src/utils/parseFormData.test.ts b/src/utils/parseFormData.test.ts
index 28d9522..658c023 100644
--- a/src/utils/parseFormData.test.ts
+++ b/src/utils/parseFormData.test.ts
@@ -76,6 +76,37 @@ test('should normalize form data with objects', () => {
   assert.deepEqual(ret, expected)
 })
 
+test('should normalize keys with structure', () => {
+  const data = 'value=1&object[id]=ent1&object[type]=entry'
+  const expected = {
+    value: 1,
+    object: { id: 'ent1', type: 'entry' },
+  }
+
+  const ret = parseFormData(data)
+
+  assert.deepEqual(ret, expected)
+})
+
+test('should normalize keys with structure with many levels', () => {
+  const data =
+    'value=1&object[array][0][id]=ent1&object[array][0][type]=entry&object[array][0][tags][0]=news&object[array][0][tags][1]=politics&object[array][1][id]=ent2&object[array][1][type]=entry&object[array][1][tags][0]=sports&empty'
+  const expected = {
+    value: 1,
+    object: {
+      array: [
+        { id: 'ent1', type: 'entry', tags: ['news', 'politics'] },
+        { id: 'ent2', type: 'entry', tags: ['sports'] },
+      ],
+    },
+    empty: undefined,
+  }
+
+  const ret = parseFormData(data)
+
+  assert.deepEqual(ret, expected)
+})
+
 test('should keep date string as string', () => {
   const data = 'value=1&date=2024-05-11T16%3A43%3A11.000Z'
   const expected = {
diff --git a/src/utils/parseFormData.ts b/src/utils/parseFormData.ts
index 505908e..049ceda 100644
--- a/src/utils/parseFormData.ts
+++ b/src/utils/parseFormData.ts
@@ -1,3 +1,5 @@
+import { isObject } from './is.js'
+
 const parseObject = (value: string) => {
   try {
     return JSON.parse(value)
@@ -13,21 +15,56 @@ const parseValue = (value?: string) =>
     ? parseObject(decodeURIComponent(fixLineBreak(value)).replace(/\+/g, ' '))
     : undefined
 
-function reducePair(
-  obj: Record<string, unknown>,
-  [key, value]: [string, string | undefined],
+function prepareKeyPart(part: string) {
+  if (part === ']') {
+    return ''
+  }
+  const num = Number.parseInt(part, 10)
+  return Number.isNaN(num)
+    ? part.endsWith(']')
+      ? part.slice(0, -1)
+      : part
+    : num
+}
+
+function parseKey(key: string): (string | number)[] {
+  return key.split('[').map(prepareKeyPart)
+}
+
+function ensureArray(value: unknown): unknown[] {
+  return Array.isArray(value) ? value : value === undefined ? [] : [value]
+}
+
+function ensureObject(value: unknown): Record<string, unknown> {
+  return isObject(value) ? value : {}
+}
+
+function setOnTarget(
+  target: unknown,
+  keys: (string | number)[],
+  value: string | undefined,
 ) {
-  if (key.endsWith('[]')) {
-    // When key ends in brackets, we have an array. This may be one of several
-    // keys with items for the array, so combine them.
-    const actualKey = key.slice(0, key.length - 2)
-    const existingValue = obj[actualKey] // eslint-disable-line security/detect-object-injection
-    const existingArray = Array.isArray(existingValue) ? existingValue : []
-    return { ...obj, [actualKey]: [...existingArray, parseValue(value)] }
+  const [key, ...restKeys] = keys
+  const isArr = key === '' || typeof key === 'number'
+  const currentTarget = isArr ? ensureArray(target) : ensureObject(target)
+  const nextTarget =
+    key === '' ? undefined : currentTarget[key as keyof typeof currentTarget]
+  const nextValue =
+    restKeys.length === 0 ? value : setOnTarget(nextTarget, restKeys, value)
+  if (key === '') {
+    ;(currentTarget as unknown[]).push(nextValue)
   } else {
-    // Parse a single value.
-    return { ...obj, [key]: parseValue(value) }
+    ;(currentTarget as unknown[])[key as number] = nextValue // This handles both arrays and object, but we have forced the typing to array, just to satisfy TS without writing extra logic.
   }
+  return currentTarget
+}
+
+function reducePair(
+  target: unknown,
+  [key, value]: [string, string | undefined],
+): unknown[] | Record<string, unknown> {
+  const keys = parseKey(key)
+  return setOnTarget(target, keys, parseValue(value))
 }
 
 export default function parseFormData(data: unknown) {
@@ -35,7 +72,7 @@ export default function parseFormData(data: unknown) {
     return data
       .split('&')
       .map((pair) => pair.split('=') as [string, string | undefined])
-      .reduce(reducePair, {})
+      .reduce(reducePair, undefined)
   } else {
     return undefined
   }
diff --git a/src/utils/stringifyFormData.test.ts b/src/utils/stringifyFormData.test.ts
index 1d6cf7d..c04fecb 100644
--- a/src/utils/stringifyFormData.test.ts
+++ b/src/utils/stringifyFormData.test.ts
@@ -92,6 +92,56 @@ test('should serialize object', () => {
   assert.equal(ret, expected)
 })
 
+test('should serialize object when setStructureInKeys is true', () => {
+  const setStructureInKeys = true
+  const data = {
+    value: 1,
+    object: { id: 'ent1', type: 'entry' },
+  }
+  const expected = 'value=1&object[id]=ent1&object[type]=entry'
+
+  const ret = stringifyFormData(data, setStructureInKeys)
+
+  assert.equal(ret, expected)
+})
+
+test('should serialize array of objects when setStructureInKeys is true', () => {
+  const setStructureInKeys = true
+  const data = {
+    value: 1,
+    array: [
+      { id: 'ent1', type: 'entry' },
+      { id: 'ent2', type: 'entry' },
+    ],
+  }
+  const expected =
+    'value=1&array[0][id]=ent1&array[0][type]=entry&array[1][id]=ent2&array[1][type]=entry'
+
+  const ret = stringifyFormData(data, setStructureInKeys)
+
+  assert.equal(ret, expected)
+})
+
+test('should serialize array and objects over several levels when setStructureInKeys is true', () => {
+  const setStructureInKeys = true
+  const data = {
+    value: 1,
+    object: {
+      array: [
+        { id: 'ent1', type: 'entry', tags: ['news', 'politics'] },
+        { id: 'ent2', type: 'entry', tags: ['sports'] },
+      ],
+    },
+    empty: undefined,
+  }
+  const expected =
+    'value=1&object[array][0][id]=ent1&object[array][0][type]=entry&object[array][0][tags][0]=news&object[array][0][tags][1]=politics&object[array][1][id]=ent2&object[array][1][type]=entry&object[array][1][tags][0]=sports&empty'
+
+  const ret = stringifyFormData(data, setStructureInKeys)
+
+  assert.equal(ret, expected)
+})
+
 test('should serialize object with one key', () => {
   const data = {
     text: 'Several words here',
diff --git a/src/utils/stringifyFormData.ts b/src/utils/stringifyFormData.ts
index 5b3aae2..5632e9b 100644
--- a/src/utils/stringifyFormData.ts
+++ b/src/utils/stringifyFormData.ts
@@ -13,19 +13,38 @@ const fixLineBreak = (value: unknown) =>
 const formatValue = (value: unknown) =>
   encodeURIComponent(formatObject(fixLineBreak(value))).replace(/%20/g, '+')
 
+const formatKeyValue = (key: string, value: unknown) =>
+  value === undefined ? key : `${key}=${formatValue(value)}`
+
+function moveStructureToKeys([key, value]: [string, unknown]):
+  | string
+  | string[] {
+  if (Array.isArray(value) || isObject(value)) {
+    return Object.entries(value).flatMap(([k, v]) =>
+      moveStructureToKeys([`${key}[${k}]`, v]),
+    )
+  } else {
+    return formatKeyValue(key, value)
+  }
+}
+
 function mapEntry([key, value]: [string, unknown]) {
   if (Array.isArray(value)) {
     // Return one key (with bracket postfix) for each value in an array
-    return value.map((val) => `${key}[]=${formatValue(val)}`)
+    return value.map((val) => formatKeyValue(`${key}[]`, val))
   } else {
     // Format a single value
-    return value === undefined ? key : `${key}=${formatValue(value)}`
+    return formatKeyValue(key, value)
   }
 }
 
-export default function stringifyFormData(data?: unknown) {
+export default function stringifyFormData(
+  data?: unknown,
+  setStructureInKeys = false,
+) {
   if (isObject(data)) {
-    return Object.entries(data).flatMap(mapEntry).join('&')
+    const fn = setStructureInKeys ? moveStructureToKeys : mapEntry
+    return Object.entries(data).flatMap(fn).join('&')
   } else {
     return undefined
   }