diff --git a/server/addresses.js b/server/addresses.js
new file mode 100644
index 0000000..c562216
--- /dev/null
+++ b/server/addresses.js
@@ -0,0 +1,129 @@
+const crypto = require('crypto')
+const fs = require('fs/promises')
+
+const storePath = '/data/store.json'
+
+async function readStore() {
+  try {
+    const data = await fs.readFile(storePath, 'utf8')
+    return JSON.parse(data)
+  } catch (error) {
+    if (error.code === 'ENOENT') {
+      return {}
+    }
+
+    throw error
+  }
+}
+
+async function writeStore(store) {
+  const temporaryPath =
+    `${storePath}.${crypto.randomBytes(8).toString('hex')}.tmp`
+
+  await fs.writeFile(
+    temporaryPath,
+    JSON.stringify(store, null, 2) + '\n',
+    {
+      mode: 0o600,
+    },
+  )
+
+  await fs.rename(temporaryPath, storePath)
+}
+
+function normalizeAddress(address) {
+  if (typeof address !== 'string') {
+    return null
+  }
+
+  const normalized = address.trim()
+
+  if (!normalized) {
+    return null
+  }
+
+  return normalized
+}
+
+function normalizeLabel(label) {
+  if (typeof label !== 'string') {
+    return undefined
+  }
+
+  const normalized = label.trim()
+
+  return normalized || undefined
+}
+
+async function listAddresses() {
+  const store = await readStore()
+
+  return Array.isArray(store.addresses)
+    ? store.addresses
+    : []
+}
+
+async function addAddress(address, label) {
+  const normalizedAddress = normalizeAddress(address)
+
+  if (!normalizedAddress) {
+    throw new Error('Bitcoin address is required')
+  }
+
+  const addresses = await listAddresses()
+
+  if (addresses.some((item) => item.address === normalizedAddress)) {
+    throw new Error('Bitcoin address is already being watched')
+  }
+
+  const entry = {
+    address: normalizedAddress,
+  }
+
+  const normalizedLabel = normalizeLabel(label)
+
+  if (normalizedLabel) {
+    entry.label = normalizedLabel
+  }
+
+  const store = await readStore()
+
+  store.addresses = [...addresses, entry]
+
+  await writeStore(store)
+
+  return entry
+}
+
+async function removeAddress(address) {
+  const normalizedAddress = normalizeAddress(address)
+
+  if (!normalizedAddress) {
+    throw new Error('Bitcoin address is required')
+  }
+
+  const store = await readStore()
+  const addresses = Array.isArray(store.addresses)
+    ? store.addresses
+    : []
+
+  const filtered = addresses.filter(
+    (item) => item.address !== normalizedAddress,
+  )
+
+  if (filtered.length === addresses.length) {
+    throw new Error('Bitcoin address is not being watched')
+  }
+
+  store.addresses = filtered
+
+  await writeStore(store)
+
+  return true
+}
+
+module.exports = {
+  listAddresses,
+  addAddress,
+  removeAddress,
+}
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