diff --git a/.gitignore b/.gitignore
index 65b85ce..064485c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,4 @@
 node_modules/
 test/
+lib/
 bin/
diff --git a/build.sh b/build.sh
deleted file mode 100755
index bfad41d..0000000
--- a/build.sh
+++ /dev/null
@@ -1,4 +0,0 @@
-mkdir -p bin
-echo '#!/usr/bin/env node' > bin/pert
-coffee -b -c --no-header -p src/pert.coffee >> bin/pert
-chmod +x bin/pert
diff --git a/package.json b/package.json
index b87a59b..a09ab9a 100644
--- a/package.json
+++ b/package.json
@@ -2,13 +2,14 @@
   "name": "pert",
   "version": "0.1.0",
   "description": "pert diagram calculator",
-  "main": "pert.coffee",
+  "main": "lib/pert.js",
   "bin": {
     "pert": "./bin/pert"
    },
   "scripts": {
-    "prepublish": "./build.sh",
-    "build": "./build.sh"
+    "prepublish": "scripts/build.sh",
+    "build": "scripts/build.sh",
+    "clean": "scripts/clean.sh"
   },
   "repository": {
     "type": "git",
diff --git a/scripts/build.sh b/scripts/build.sh
new file mode 100755
index 0000000..c2eb0c7
--- /dev/null
+++ b/scripts/build.sh
@@ -0,0 +1,5 @@
+mkdir -p bin lib
+echo '#!/usr/bin/env node' > bin/pert
+coffee -b -c --no-header -p src/pert-cli.coffee >> bin/pert
+chmod +x bin/pert
+coffee -b -c --no-header -p src/pert.coffee > lib/pert.js
diff --git a/scripts/clean.sh b/scripts/clean.sh
new file mode 100755
index 0000000..3263499
--- /dev/null
+++ b/scripts/clean.sh
@@ -0,0 +1,2 @@
+#!/bin/bash
+rm -rf bin lib
diff --git a/src/pert-cli.coffee b/src/pert-cli.coffee
new file mode 100755
index 0000000..6ffc38c
--- /dev/null
+++ b/src/pert-cli.coffee
@@ -0,0 +1,40 @@
+#!/usr/bin/env coffee
+chalk = require 'chalk'
+cli = require 'commander'
+fs = require 'fs'
+pert = require '../lib/pert.js'
+
+ex = [{id: 0, depends: [], duration: 2}, { id: 1, depends: [0], duration: 3},{id: 2, depends: [0,1], duration: 4}]
+
+cli
+  .version '0.1'
+  .usage 'loads activity data from JSON and computes the possible activity delays'
+  .option '--verbose', 'be verbose (for debugging)'
+
+didSomething = no
+
+cli
+  .command 'example'
+  .description 'show an example of the JSON data format'
+  .action ->
+    didSomething = yes
+    console.log chalk.bold.green('Before:'), ex
+    console.log chalk.bold.green('After calculations:'), pert.calculate ex
+    console.log chalk.green 'Tip:',chalk.bold 'optional fields can be freely included in the input data'
+
+cli
+  .command 'calculate <file>'
+  .description 'calculate data on given JSON document'
+  .alias 'c'
+  .option '-j, --json', 'output json data'
+  .action (file,options) ->
+    didSomething = yes
+    fs.readFile file, (error,content) ->
+      if error then err error
+      else
+        if options.json then console.log JSON.stringify (pert.calculate JSON.parse(content))
+        else console.log pert.calculate JSON.parse(content)
+
+cli.parse process.argv
+
+if !didSomething then console.log chalk.green('Tip:'), 'see', chalk.bold(cli.name()+' --help')
diff --git a/src/pert.coffee b/src/pert.coffee
index 4719945..c5f8b74 100755
--- a/src/pert.coffee
+++ b/src/pert.coffee
@@ -1,85 +1,52 @@
-#!/usr/bin/env coffee
 chalk = require 'chalk'
-cli = require 'commander'
 fs = require 'fs'
 
-log = (x...) -> if cli.verbose then console.log chalk.bold("Log:"), x...
-err = (x...) -> console.log chalk.bold (chalk.red "Error:"), x...
+pert = 
+  log: (x...) -> if @verbose then console.log chalk.bold("Pert:"), x...
+  err: (x...) -> console.log chalk.bold (chalk.red "Pert:"), x...
 
-# Returns the highest number in an array of numbers
-maxa = (l) -> return Math.max.apply null, l
+  # Returns the highest number in an array of numbers
+  maxa: (l) -> return Math.max.apply null, l
 
-# Find the activity with given id
-toActivity = (id,list) ->
-  if !list? then err "list is",list
-  item = {}
-  list.forEach (x) -> if x.id is id then item = x
-  return item
+  # Find the activity with given id
+  toActivity: (id,list) ->
+    if !list? then pert.err "list is",list
+    item = {}
+    list.forEach (x) -> if x.id is id then item = x
+    return item
 
-# Find the item 
-calculateEndDay = (item,list) ->
-  if !item.startDay?
-    log "calculating start day of",item.id
-    item.startDay = calculateStartDay item, list
-  log "start day of",item.id,"is",item.startDay
-  item.endDay = item.startDay + item.duration
-  log "end day of",item.id,"is",item.endDay
-  return item.endDay
+  # Find the item 
+  calculateEndDay: (item,list) ->
+    if !item.startDay?
+      pert.log "calculating start day of",item.id
+      item.startDay = pert.calculateStartDay item, list
+    pert.log "start day of",item.id,"is",item.startDay
+    item.endDay = item.startDay + item.duration
+    pert.log "end day of",item.id,"is",item.endDay
+    return item.endDay
 
-# Find out which day the activity starts
-calculateStartDay = (item,list) ->
-  if !item.depends? or item.depends.length is 0 then return item.startDay = 0
-  item.startDay = maxa item.depends.map((x) -> toActivity x,list).map((x) -> calculateEndDay x, list)
-  log "start day of",item.id,"is",item.startDay
-  # write max delay time to each depend
-  item.depends.forEach (x) ->
-    log "checking permittedDelay to dependency", x, "of", item
-    i = toActivity x, list
-    if !i.permittedDelay?
-      i.permittedDelay = item.startDay - calculateEndDay i, list
-      log "written permittedDelay to dependency", x, "of", item, "as", i.permittedDelay
-    else log "aborting permittedDelay: already calculated"
-    log "permitted delay of",x,"is",i.permittedDelay
-  return item.startDay
+  # Find out which day the activity starts
+  calculateStartDay: (item,list) ->
+    if !item.depends? or item.depends.length is 0 then return item.startDay = 0
+    item.startDay = pert.maxa item.depends.map((x) -> pert.toActivity x,list).map((x) -> pert.calculateEndDay x, list)
+    pert.log "start day of",item.id,"is",item.startDay
+    # write max delay time to each depend
+    item.depends.forEach (x) ->
+      pert.log "checking permittedDelay to dependency", x, "of", item
+      i = pert.toActivity x, list
+      if !i.permittedDelay?
+        i.permittedDelay = item.startDay - pert.calculateEndDay i, list
+        pert.log "written permittedDelay to dependency", x, "of", item, "as", i.permittedDelay
+      else pert.log "aborting permittedDelay: already calculated"
+      pert.log "permitted delay of",x,"is",i.permittedDelay
+    return item.startDay
 
-# Find out which activity has the highest id
-highestID = (list) -> return maxa(list.map (x) -> x.id)
+  # Find out which activity has the highest id
+  highestID: (list) -> return pert.maxa(list.map (x) -> x.id)
 
-calculate = (list) ->
-  calculateEndDay (toActivity highestID(list), list), list
-  return list
+  calculate: (list,verbose) ->
+    pert.verbose = verbose
+    pert.calculateEndDay (pert.toActivity pert.highestID(list), list), list
+    return list
 
-ex = [{id: 0, depends: [], duration: 2}, { id: 1, depends: [0], duration: 3},{id: 2, depends: [0,1], duration: 4}]
-
-cli
-  .version '0.1'
-  .usage 'loads activity data from JSON and computes the possible activity delays'
-  .option '--verbose', 'be verbose (for debugging)'
-
-didSomething = no
-
-cli
-  .command 'example'
-  .description 'show an example of the JSON data format'
-  .action ->
-    didSomething = yes
-    console.log chalk.bold.green('Before:'), ex
-    console.log chalk.bold.green('After calculations:'), calculate ex
-    console.log chalk.green 'Tip:',chalk.bold 'optional fields can be freely included in the input data'
-
-cli
-  .command 'calculate <file>'
-  .description 'calculate data on given JSON document'
-  .alias 'c'
-  .option '-j, --json', 'output json data'
-  .action (file,options) ->
-    didSomething = yes
-    fs.readFile file, (error,content) ->
-      if error then err error
-      else
-        if options.json then console.log JSON.stringify (calculate JSON.parse(content))
-        else console.log calculate JSON.parse(content)
-
-cli.parse process.argv
-
-if !didSomething then console.log chalk.green('Tip:'), 'see', chalk.bold(cli.name()+' --help')
+module.exports = pert