diff --git a/README.md b/README.md
index d475f5f..8c7aa3b 100644
--- a/README.md
+++ b/README.md
@@ -6,7 +6,9 @@ Uses the implementation of Rabin fingerprinting from [LBFS](https://github.com/f
 
 Rabin fingerprinting is useful for finding the chunks of a file that differ from a previous version. It's one implementation of a technique called "Content-defined chunking", meaning the chunk boundaries are determinstic to the content (as opposed to "fixed-sized chunking").
 
-## API
+Theres a JavaScript API and an accompanying command-line tool.
+
+## JavaScript API
 
 ### `var createRabin = require('rabin')`
 
@@ -16,7 +18,7 @@ Rabin fingerprinting is useful for finding the chunks of a file that differ from
 
 `rabin` is a duplex stream. You write raw data in, and buffers chunked by rabin fingerprints will be written out.
 
-## Example
+## JavaScript Example
 
 ```js
 // require and create an instance
@@ -32,3 +34,20 @@ rabin.on('data', function (chunk) {
   // and splitting on each rabin fingerprint found
 })
 ```
+
+## CLI API
+
+```
+$ npm install rabin -g
+$ rabin myfile.txt --bits=14 --min=8192 --max=32768 # defaults
+{"length":12182,"offset":0,"hash":"5df6245b5897336ebf611d7f10fb90eea2d63c5b9ec9ad76dfb1ac72b8249dcb"}
+{"length":13190,"offset":12182,"hash":"67d5aaac9cf7b8432cb3c8071d726dc38f1138957c30719f8b166116a90950a1"}
+{"length":11609,"offset":25372,"hash":"976a0e3dc43de3abdf50b984a102c5fb7c2550e3dc5e44e4a8f7d4241276683b"}
+{"length":10010,"offset":36981,"hash":"7145d10f93ea03e6c8b4dd5ab148e2c3c08f9c71bf71c7559dffdfcef48112c1"}
+{"length":13623,"offset":46991,"hash":"76470d5047f9fb31bd75364d90355fdbf913aaa1df934251f43c894f01381f1b"}
+{"length":8197,"offset":60614,"hash":"88abce05bc75f72cdafeabd5125eb46fa8f73eab2d75a29076aeb3f99ef35548"}
+{"length":16242,"offset":68811,"hash":"08d60789c1e901d6a8e474aeb5de4746af1648e7f3a4ac7a3dba87d9e73fca56"}
+{"length":14947,"offset":85053,"hash":"4224e6f4361fa8bdefb9d8e10ebd046e2869af2c44ea7e84c7efaeedd5423b30"}
+average 12500
+```
+
diff --git a/bindings.cc b/bindings.cc
index a594124..5e64d1f 100644
--- a/bindings.cc
+++ b/bindings.cc
@@ -32,13 +32,21 @@ void get_fingerprints(rabin_t *hasher, Local<Array> bufs, Local<Array> lengths)
 NAN_METHOD(Initialize) {
   if (instance_counter >= 1024) return Nan::ThrowError("the value of instance_counter is too damn high");
   struct rabin_t *hasher = (struct rabin_t *) malloc(sizeof(struct rabin_t));
+
+  if (!info[0]->IsNumber()) return Nan::ThrowError("first arg must be a number");
+  if (!info[1]->IsNumber()) return Nan::ThrowError("second arg must be a number");
+  if (!info[2]->IsNumber()) return Nan::ThrowError("third arg must be a number");
+
+  hasher->average_bits = info[0]->Uint32Value();
+  hasher->minsize = info[1]->Uint32Value();
+  hasher->maxsize = info[2]->Uint32Value();
+
+  // Open a pull request if you need these to be configurable
+  hasher->mask = ((1<<hasher->average_bits)-1);
   hasher->polynomial = 0x3DA3358B4DC173LL;
   hasher->polynomial_degree = 53;
-  hasher->average_bits = 14;
-  hasher->minsize = 8 * 1024;
-  hasher->maxsize = 32 * 1024;
-  hasher->mask = ((1<<hasher->average_bits)-1);
   hasher->polynomial_shift = (hasher->polynomial_degree-8);
+
   rabin_init(hasher);
   instances[instance_counter++] = hasher;
   info.GetReturnValue().Set(instance_counter - 1);
diff --git a/cli.js b/cli.js
index caeb872..78f446d 100755
--- a/cli.js
+++ b/cli.js
@@ -1,9 +1,10 @@
 #!/usr/bin/env node
 var fs = require('fs')
 var crypto = require('crypto')
-var rabin = require('./')()
+var args = require('minimist')(process.argv.slice(2))
+var rabin = require('./')(args)
 var offset = 0
-var rs = fs.createReadStream(process.argv[2])
+var rs = fs.createReadStream(args._[0])
 var count = 0
 rs.pipe(rabin).on('data', function (ch) {
   offset += ch.length
diff --git a/index.js b/index.js
index f7ffac6..a682966 100644
--- a/index.js
+++ b/index.js
@@ -6,11 +6,14 @@ var debug = require('debug')('rabin')
 
 module.exports = Rabin
 
-function Rabin () {
-  if (!(this instanceof Rabin)) return new Rabin()
+function Rabin (opts) {
+  if (!(this instanceof Rabin)) return new Rabin(opts)
   this.destroyed = false
   this.rabinEnded = false
-  this.rabin = rabin.initialize()
+  var avgBits = +opts.bits || 12
+  var min = +opts.min || 8 * 1024
+  var max = +opts.max || 32 * 1024
+  this.rabin = rabin.initialize(avgBits, min, max)
   this.nextCb = null
   this.buffers = new BufferList()
   this.on('finish', function () {
diff --git a/package.json b/package.json
index 9022572..49f432d 100644
--- a/package.json
+++ b/package.json
@@ -6,6 +6,7 @@
   "bin": {
     "rabin": "cli.js"
   },
+  "keywords": ["rabin", "cdc", "chunking", "fingerprint", "rolling hash", "dedupe", "deduplication", "rsync"],
   "scripts": {
     "test": "echo \"Error: no test specified\" && exit 1",
     "install": "prebuild --download && echo \"Installed prebuilt binary successfully.\n\"",
@@ -18,6 +19,7 @@
     "bindings": "^1.2.1",
     "bl": "^1.0.0",
     "debug": "^2.2.0",
+    "minimist": "^1.2.0",
     "nan": "^2.1.0",
     "prebuild": "^2.6.2",
     "readable-stream": "^2.0.4"