diff --git a/Justfile b/Justfile
index 52d9c30..977ea88 100644
--- a/Justfile
+++ b/Justfile
@@ -9,33 +9,47 @@ default:
     @just --list
 
 # start nerfs artifact builder in demo mode
+[group('build')]
 run mode: compile
     $GOBIN/nerfs {{mode}}
 
 # compile the nerfs executable
+[group('build')]
 compile: tidy
     cd cmds/nerfs && go install
 
 # tidy up Go modules
+[group('build')]
 tidy:
     go mod tidy
 
 # vet the nerfs source tree
+[group('lint')]
 vet:
     go vet ./...
 
 # run go test on the source tree
+[group('testing')]
 tests:
     go test -race ./...
 
+# run specific unit test
+[group('testing')]
+[no-cd]
+test unit:
+    go test -v -count=1 -race -run {{unit}} 2>/dev/null
+
 # lint the nerfs source tree
+[group('lint')]
 lint: vet
     $GOBIN/golangci-lint run --config $scripts/golangci.yaml
 
 # show host system information
+[group('build')]
 @sysinfo:
     echo "{{os()/arch()}} {{num_cpus()}}c"
 
 # locally install build dependencies
+[group('build')]
 init:
     go install github.com/golangci/golangci-lint/v2/cmd/golangci-lint@v2.11.4
diff --git a/cmds/nerfs/commands/commands.go b/cmds/nerfs/commands/commands.go
index 203f67c..c696ae5 100644
--- a/cmds/nerfs/commands/commands.go
+++ b/cmds/nerfs/commands/commands.go
@@ -1,10 +1,10 @@
 package commands
 
 import (
-	"fmt"
 	"os"
 
 	"cattlecloud.net/go/babycli"
+	"cattlecloud.net/go/ulog"
 	"cattlecloud.net/nerfs/cmds/nerfs/domains"
 	"cattlecloud.net/nerfs/cmds/nerfs/wordlist"
 )
@@ -40,17 +40,19 @@ func invoke(args []string) babycli.Code {
 						},
 					},
 					Function: func(c *babycli.Component) babycli.Code {
+						log := ulog.New("nerfs")
+
 						output := c.GetString("output")
 
 						buildDomains := domains.NewBuilder()
 						if err := buildDomains.Build(output); err != nil {
-							fmt.Println("build failure:", err)
+							log.E.Fmt("unable to build domains list: %v", err)
 							return babycli.Failure
 						}
 
 						buildWords := wordlist.NewBuilder()
 						if err := buildWords.Build(output); err != nil {
-							fmt.Println("build failure:", err)
+							log.E.Fmt("unable to build words list: %v", err)
 							return babycli.Failure
 						}
 
diff --git a/nerfs.go b/nerfs.go
index 86559c6..201f3cc 100644
--- a/nerfs.go
+++ b/nerfs.go
@@ -14,17 +14,15 @@ import (
 
 const (
 	DomainsFile = "domains.txt"
-	WordsFile   = "wordlist.txt"
+	WordsFile   = "wordlist.json"
 )
 
 // An Artifact contains the in-memory optimized form of the domain and word
 // block-list files created by the nerfs tool.
 //
-// Create an Artifact by calling Load() with the directory of the compiled
-// artifacts.
-type Artifact struct {
-	domains *set.Set[string]
-	words   []*regexp.Regexp
+// Call Synopsis on some text to analyze it.
+type Artifact interface {
+	Synopsis(r io.Reader) *Synopsis
 }
 
 // A Synopsis contains the result of analyzing some text.
@@ -36,6 +34,11 @@ type Synopsis struct {
 	Words int
 }
 
+type artifact struct {
+	domains *set.Set[string]
+	words   []*regexp.Regexp
+}
+
 // Any returns whether any domains or words appear on the block lists.
 func (s *Synopsis) Any() bool {
 	return s.Domains > 0 || s.Words > 0
@@ -47,7 +50,7 @@ func (s *Synopsis) Any() bool {
 // Note that this should be used carefully - scanning large text consumes lots
 // of CPU due to regular expression matching against every token. Many use cases
 // need only scan against blocked domains which is must faster.
-func (a *Artifact) Synopsis(r io.Reader) *Synopsis {
+func (a *artifact) Synopsis(r io.Reader) *Synopsis {
 	syn := new(Synopsis)
 	scanner := bufio.NewScanner(r)
 	scanner.Split(bufio.ScanWords)
@@ -63,7 +66,7 @@ func (a *Artifact) Synopsis(r io.Reader) *Synopsis {
 	return syn
 }
 
-func (a *Artifact) matchDomain(s string) bool {
+func (a *artifact) matchDomain(s string) bool {
 	s, _ = strings.CutPrefix(s, "https://")
 	s, _ = strings.CutPrefix(s, "http://")
 	if i := strings.IndexAny(s, "/?#"); i >= 0 {
@@ -72,7 +75,7 @@ func (a *Artifact) matchDomain(s string) bool {
 	return a.domains.Contains(s)
 }
 
-func (a *Artifact) matchWord(s string) bool {
+func (a *artifact) matchWord(s string) bool {
 	for _, reg := range a.words {
 		if reg.MatchString(s) {
 			return true
@@ -81,7 +84,7 @@ func (a *Artifact) matchWord(s string) bool {
 	return false
 }
 
-func Load(directory string) (*Artifact, error) {
+func Load(directory string) (Artifact, error) {
 	domainsFile := filepath.Join(directory, DomainsFile)
 	wordsFile := filepath.Join(directory, WordsFile)
 
@@ -95,7 +98,7 @@ func Load(directory string) (*Artifact, error) {
 		return nil, werr
 	}
 
-	return &Artifact{
+	return &artifact{
 		domains: domains,
 		words:   words,
 	}, nil
diff --git a/nerfs_test.go b/nerfs_test.go
index 265164a..7dd790e 100644
--- a/nerfs_test.go
+++ b/nerfs_test.go
@@ -62,14 +62,14 @@ func TestArtifact_Load(t *testing.T) {
 
 	art, lerr := Load(d)
 	must.NoError(t, lerr)
-	must.Size(t, 3, art.domains)
-	must.Len(t, 2, art.words)
+	must.Size(t, 3, art.(*artifact).domains)
+	must.Len(t, 2, art.(*artifact).words)
 }
 
 func TestSynopsis_matching(t *testing.T) {
 	t.Parallel()
 
-	a := &Artifact{
+	a := &artifact{
 		domains: set.From([]string{"example.com", "example.org", "example.xyz"}),
 		words: []*regexp.Regexp{
 			regexp.MustCompile(`p[oO0]+p`),
@@ -116,7 +116,7 @@ visit example.org we have pOop and f4rts! example.xyz and example.com too!
 func TestArtifact_matchDomain(t *testing.T) {
 	t.Parallel()
 
-	a := &Artifact{
+	a := &artifact{
 		domains: set.From([]string{"example.com", "example.xyz"}),
 	}