diff --git a/Makefile b/Makefile
index 9a61cd1..d205cf6 100644
--- a/Makefile
+++ b/Makefile
@@ -6,7 +6,7 @@ quality:
 
 test:
 	go test -coverprofile=coverage
-	go run main.go -coverage $$(go tool cover -func=coverage | grep total | cut -d$$'\t' -f6 | cut -d'.' -f1) > coverage.svg
+	go run main.go $$(go tool cover -func=coverage | grep total | cut -d$$'\t' -f5 | cut -d'.' -f1) > coverage.svg
 
 build:
 	GOOS=darwin GOARCH=386 go build -o covbadger-darwin
diff --git a/README.md b/README.md
index 0f13df9..8d568ae 100644
--- a/README.md
+++ b/README.md
@@ -2,27 +2,14 @@
 
 ![Coverage](https://rawgit.com/imsky/covbadger/master/coverage.svg)
 
-`covbadger` generates code coverage badges from Cobertura-compatible XML coverage reports.
+`covbadger` generates code coverage badges.
 
-## Compatibility
+## Usage
 
-Several "standard" coverage libraries for various languages have Cobertura output built in:
-
-* JavaScript supports Cobertura with [istanbul](https://istanbul.js.org/)
-* Python supports Cobertura with [nosetest](http://nose.readthedocs.io/en/latest/) and [pytest](https://docs.pytest.org/en/latest/)
-* Scala supports Cobertura with [scoverage](https://github.com/scoverage/scalac-scoverage-plugin)
-
-There are also several coverage format conversion tools:
-
-* Go has [gocov-xml](https://github.com/AlekSi/gocov-xml)
-* Erlang has [covertool](https://github.com/idubrov/covertool)
-* .NET has [OpenCoverToCoberturaConverter](https://github.com/danielpalme/OpenCoverToCoberturaConverter)
-* JaCoCo has [cover2cover](https://github.com/rix0rrr/cover2cover)
-* Finally, LCOV reports can be converted using [lcov-to-cobertura-xml](https://github.com/eriwen/lcov-to-cobertura-xml)
-
-## Roadmap
-
-* Support for diffing an existing badge to get coverage delta
+```
+# generate a badge that shows 97% coverage
+covbadger 97
+```
 
 ## License
 
diff --git a/main.go b/main.go
index 9b2ced7..5bdff2d 100644
--- a/main.go
+++ b/main.go
@@ -2,20 +2,13 @@ package main
 
 import (
 	"bytes"
-	"encoding/xml"
 	"errors"
 	"flag"
 	"fmt"
-	"io/ioutil"
-	"math"
+	"strconv"
 	"text/template"
 )
 
-//CoverageReport represents an individual coverage report
-type CoverageReport struct {
-	LineRate float64 `xml:"line-rate,attr"`
-}
-
 //Badge represents a coverage badge
 type Badge struct {
 	Coverage int
@@ -51,7 +44,7 @@ var _badgeTemplate string = `<svg xmlns="http://www.w3.org/2000/svg" width="96"
 
 func RenderBadge(coverage int) (string, error) {
 	if coverage < 0 || coverage > 100 {
-		return "", errors.New("Invalid coverage: " + string(coverage))
+		return "", errors.New("Invalid coverage: " + strconv.Itoa(coverage))
 	}
 
 	var buffer bytes.Buffer
@@ -73,51 +66,27 @@ func RenderBadge(coverage int) (string, error) {
 	return buffer.String(), nil
 }
 
-func GetCoverageFromReports(files []string) int {
-	var sum float64 = 0
-	reports := make([]CoverageReport, 0, len(files))
-
-	for _, fileName := range files {
-		var report CoverageReport
-
-		in, err := ioutil.ReadFile(fileName)
-
-		if err != nil {
-			panic(err)
-		}
-
-		xml.Unmarshal(in, &report)
-		sum += report.LineRate
-		reports = append(reports, report)
-	}
-
-	return int(math.Floor(sum / float64(len(reports)) * 100))
-}
-
-func Run(files []string, coverage int) {
-	var badge string
-
-	if len(files) == 0 && coverage == 0 {
+func Run(args []string) {
+	if len(args) != 1 {
 		flag.Usage()
 		return
-	} else if len(files) > 0 {
-		badge, _ = RenderBadge(GetCoverageFromReports(files))
-	} else if coverage > 0 {
-		badge, _ = RenderBadge(coverage)
 	}
 
-	fmt.Println(badge)
+	coverage, _ := strconv.Atoi(args[0])
+	badge, err := RenderBadge(coverage)
+
+	if err != nil {
+		panic(err)
+	} else {
+		fmt.Println(badge)
+	}
 }
 
 func main() {
-	var coverageFlag int
-
-	flag.IntVar(&coverageFlag, "coverage", 0, "custom coverage value")
-	flag.Parse()
 	flag.Usage = func() {
-		fmt.Println(`Usage: covbadger [files]`)
-		flag.PrintDefaults()
+		fmt.Println(`Usage: covbadger [coverage]`)
 	}
 
-	Run(flag.Args(), coverageFlag)
+	flag.Parse()
+	Run(flag.Args())
 }
diff --git a/main_test.go b/main_test.go
index 76cc26d..1aeedb1 100644
--- a/main_test.go
+++ b/main_test.go
@@ -24,23 +24,6 @@ var expected string = `<svg xmlns="http://www.w3.org/2000/svg" width="96" height
     </g>
 </svg>`
 
-func TestGetCoverageFromReports(t *testing.T) {
-	coverage := GetCoverageFromReports([]string{"test-report.xml"})
-
-	if coverage != 90 {
-		t.Errorf("Coverage is %v, expected 90", coverage)
-	}
-
-	defer func() {
-		if r := recover(); r == nil {
-			t.Errorf("Bad reports did not cause errors")
-		}
-	}()
-
-	badFiles := []string{"xxx.go"}
-	GetCoverageFromReports(badFiles)
-}
-
 func TestRenderBadge(t *testing.T) {
 	var err error
 	badge, _ := RenderBadge(90)
@@ -88,7 +71,13 @@ func TestRenderBadge(t *testing.T) {
 }
 
 func TestCovbadger(t *testing.T) {
-	Run([]string{"test-report.xml"}, 0)
-	Run([]string{}, 99)
+	defer func() {
+		if r := recover(); r == nil {
+			t.Errorf("Invalid coverage value did not throw an error")
+		}
+	}()
+
 	main()
+	Run([]string{"99"})
+	Run([]string{"-99"})
 }