diff --git a/.gitignore b/.gitignore
index 119db73..504b5c6 100644
--- a/.gitignore
+++ b/.gitignore
@@ -33,6 +33,7 @@ node_modules
 
 # Temporary / data folders
 .tmp
+.data
 data/
 
 # Build directory
diff --git a/.npmignore b/.npmignore
index 6b8f416..4954381 100644
--- a/.npmignore
+++ b/.npmignore
@@ -36,6 +36,7 @@ src/
 
 # Test directory
 test/
+.data
 
 .eslintrc
 .babelrc
diff --git a/README.md b/README.md
index 3b679c7..f01eb3e 100644
--- a/README.md
+++ b/README.md
@@ -2,7 +2,7 @@
 
 [![Build Status](https://travis-ci.org/blockai/fs-tus-store.svg?branch=master)](https://travis-ci.org/blockai/fs-tus-store)
 
-WIP
+WIP.
 
 ## Install
 
@@ -14,4 +14,21 @@ Requires Node v6+
 
 ## Usage
 
-See [./test](./test) directory for usage examples.
\ No newline at end of file
+See [./test](./test) directory for usage examples.
+
+All methods return promises.
+
+### Creating client
+
+```javascript
+import initFsStore from 'tus-fs-store'
+const store  = initFsStore({ directory: './path/to/base/directory' })
+```
+
+### info(key)
+
+Resolves to an `{ uploadOffset[, uploadLength, uploadMetadata] }` object.
+
+### create(key[, { uploadLength, uploadMetadata }])
+
+### write(key, readStream)
diff --git a/package.json b/package.json
index fc28860..bd01562 100644
--- a/package.json
+++ b/package.json
@@ -37,9 +37,11 @@
     "blue-tape": "^1.0.0",
     "cz-conventional-changelog": "^1.2.0",
     "eslint-config-blockai": "^1.0.1",
+    "mkdirp": "^0.5.1",
     "nodemon": "^1.10.2",
     "rimraf": "^2.5.4",
-    "semantic-release": "^4.3.5"
+    "semantic-release": "^4.3.5",
+    "string-to-stream": "^1.1.0"
   },
   "release": {
     "debug": false,
@@ -51,5 +53,8 @@
     "commitizen": {
       "path": "cz-conventional-changelog"
     }
+  },
+  "dependencies": {
+    "pump": "^1.0.1"
   }
-}
\ No newline at end of file
+}
diff --git a/src/index.js b/src/index.js
index 45a9011..9814f5d 100644
--- a/src/index.js
+++ b/src/index.js
@@ -1,3 +1,77 @@
-export default () => {
+import path from 'path'
+import fs from 'fs'
+import pump from 'pump'
 
+// promisify
+const readFile = (file) => new Promise((resolve, reject) => {
+  fs.readFile(file, (err, data) => {
+    if (err) return reject(err)
+    resolve(data)
+  })
+})
+const writeFile = (file, data) => new Promise((resolve, reject) => {
+  fs.writeFile(file, data, (err) => {
+    if (err) return reject(err)
+    resolve(data)
+  })
+})
+const stat = (file) => new Promise((resolve, reject) => {
+  fs.stat(file, (err, statObj) => {
+    if (err) return reject(err)
+    resolve(statObj)
+  })
+})
+
+export default ({
+  directory = '.fs-tus-store',
+} = {}) => {
+  const absoluteDir = path.resolve(directory)
+  // Returns { uploadOffset[, uploadLength] }
+
+  // TODO: convert key to base64 or validate it?
+  const keyPath = (key) => path.join(absoluteDir, key)
+  const keyInfoPath = (key) => `${keyPath(key)}.info`
+
+  const getKeyInfo = (key) => readFile(keyInfoPath(key))
+    .then(data => JSON.parse(data))
+
+  const setKeyInfo = (key, infoObj) => Promise.resolve()
+    .then(() => JSON.stringify(infoObj))
+    .then(data => writeFile(keyInfoPath(key), data))
+
+  const getKeyOffset = (key) => stat(keyPath(key))
+    .then(({ size }) => size)
+
+  const touchKey = (key) => writeFile(keyPath(key), '')
+
+  // TODO: fail if key already exists?
+  const create = (key, { uploadLength, uploadMetadata } = {}) => (
+    setKeyInfo(key, { uploadLength, uploadMetadata })
+      .then(() => touchKey(key))
+  )
+
+  const info = key => getKeyInfo(key)
+    .then(infoObj => (
+      getKeyOffset(key)
+        .then((uploadOffset) => ({
+          ...infoObj,
+          uploadOffset,
+        }))
+    ))
+
+  const write = (key, rs) => new Promise((resolve, reject) => {
+    const ws = fs.createWriteStream(keyPath(key), {
+      flags: 'a', // append to file
+    })
+    pump(rs, ws, (err) => {
+      if (err) return reject(err)
+      resolve()
+    })
+  })
+
+  return {
+    info,
+    create,
+    write,
+  }
 }
diff --git a/test/index.test.js b/test/index.test.js
index 75c2fde..b973a8f 100644
--- a/test/index.test.js
+++ b/test/index.test.js
@@ -1,7 +1,72 @@
 import test from 'blue-tape'
-import init from '../src'
+import rimraf from 'rimraf'
+import mkdirp from 'mkdirp'
+import str from 'string-to-stream'
 
-test('todo', (t) => {
-  t.ok(!!init)
-  t.end()
+import initFsStore from '../src'
+
+const resetStore = () => {
+  const directory = `${__dirname}/.data`
+  rimraf.sync(directory)
+  mkdirp.sync(directory)
+  return initFsStore({ directory })
+}
+
+const store = resetStore()
+
+test('info - unknown key', (t) => {
+  store
+    .info('unknown-key')
+    .catch((err) => {
+      t.ok(err instanceof Error)
+      t.end()
+    })
 })
+
+test('info - foo- unknown key', (t) => {
+  store
+    .info('foo')
+    .catch((err) => {
+      t.ok(err instanceof Error)
+      t.end()
+    })
+})
+
+test('create foo', () => (
+  store
+    .create('foo', { uploadLength: 'bar'.length })
+))
+
+test('info foo', (t) => (
+  store
+    .info('foo')
+    .then(({ uploadOffset, uploadLength }) => {
+      t.equal(uploadOffset, 0)
+      t.equal(uploadLength, 3)
+    })
+))
+
+test('write ba to foo', () => (
+  store
+    .write('foo', str('ba'))
+))
+
+test('info foo', (t) => (
+  store
+    .info('foo')
+    .then(({ uploadOffset, uploadLength }) => {
+      t.equal(uploadOffset, 2)
+      t.equal(uploadLength, 3)
+    })
+))
+
+test('write r to foo', () => store.write('foo', str('r')))
+
+test('info foo', (t) => (
+  store
+    .info('foo')
+    .then(({ uploadOffset, uploadLength }) => {
+      t.equal(uploadOffset, 3)
+      t.equal(uploadLength, 3)
+    })
+))