diff --git a/cmd/bindown/completion.go b/cmd/bindown/completion.go
new file mode 100644
index 0000000..966691c
--- /dev/null
+++ b/cmd/bindown/completion.go
@@ -0,0 +1,110 @@
+package main
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+
+	"github.com/killa-beez/gopkgs/sets/builtins"
+	"github.com/posener/complete"
+	"github.com/willabides/bindown/v2"
+)
+
+func findConfigFileForPredictor(args []string) string {
+	for i, arg := range args {
+		if len(args) == i+1 {
+			continue
+		}
+		if arg != "--configfile" {
+			continue
+		}
+		return multifileFindExisting(args[i+1])
+	}
+	cf, ok := os.LookupEnv("BINDOWN_CONFIG_FILE")
+	if ok {
+		return multifileFindExisting(cf)
+	}
+	return multifileFindExisting(kongVars["configfile_default"])
+}
+
+func predictorConfig(args []string) *bindown.ConfigFile {
+	path := findConfigFileForPredictor(args)
+	if path == "" {
+		return nil
+	}
+	configFile, err := bindown.LoadConfigFile(path)
+	if err != nil {
+		return nil
+	}
+	return configFile
+}
+
+func allBins(cfg *bindown.ConfigFile) []string {
+	if cfg == nil {
+		return []string{}
+	}
+	bins := builtins.NewStringSet(len(cfg.Downloaders) * 10)
+	for dlName, downloaders := range cfg.Downloaders {
+		for _, dl := range downloaders {
+			if dl.BinName == "" {
+				bins.Add(dlName)
+				continue
+			}
+			bins.Add(dl.BinName)
+		}
+	}
+	return bins.Values()
+}
+
+var binPredictor = complete.PredictFunc(func(a complete.Args) []string {
+	cfg := predictorConfig(a.Completed)
+	return complete.PredictSet(allBins(cfg)...).Predict(a)
+})
+
+var binPathPredictor = complete.PredictFunc(func(a complete.Args) []string {
+	cfg := predictorConfig(a.Completed)
+	bins := allBins(cfg)
+	dir, _ := filepath.Split(a.Last)
+	for i, bin := range bins {
+		bins[i] = filepath.Join(dir, bin)
+	}
+	return complete.PredictOr(
+		complete.PredictDirs("*"),
+		complete.PredictSet(bins...),
+	).Predict(a)
+})
+
+var osPredictor = complete.PredictSet(strings.Split(goosVals, "\n")...)
+
+//from `go tool dist list | cut -f 1 -d '/' | sort | uniq`
+const goosVals = `aix
+android
+darwin
+dragonfly
+freebsd
+illumos
+js
+linux
+nacl
+netbsd
+openbsd
+plan9
+solaris
+windows`
+
+var archPredictor = complete.PredictSet(strings.Split(goarchVals, "\n")...)
+
+//from `go tool dist list | cut -f 2 -d '/' | sort | uniq`
+const goarchVals = `386
+amd64
+amd64p32
+arm
+arm64
+mips
+mips64
+mips64le
+mipsle
+ppc64
+ppc64le
+s390x
+wasm`
diff --git a/cmd/bindown/config.go b/cmd/bindown/config.go
index 8a4ee20..2326676 100644
--- a/cmd/bindown/config.go
+++ b/cmd/bindown/config.go
@@ -40,7 +40,7 @@ func (c configFmtCmd) Run() error {
 }
 
 type configUpdateChecksumsCmd struct {
-	TargetFile string `kong:"required=true,arg,help=${config_checksums_bin_help}"`
+	TargetFile string `kong:"required=true,arg,help=${config_checksums_bin_help},predictor=bin"`
 }
 
 func (d *configUpdateChecksumsCmd) Run(kctx *kong.Context) error {
@@ -87,7 +87,7 @@ func (d *configUpdateChecksumsCmd) Run(kctx *kong.Context) error {
 }
 
 type configValidateCmd struct {
-	Bin string `kong:"required=true,arg,help=${config_validate_bin_help}"`
+	Bin string `kong:"required=true,arg,help=${config_validate_bin_help},predictor=bin"`
 }
 
 func (d configValidateCmd) Run(kctx *kong.Context) error {
diff --git a/cmd/bindown/download.go b/cmd/bindown/download.go
index 2b3a39d..135df2b 100644
--- a/cmd/bindown/download.go
+++ b/cmd/bindown/download.go
@@ -19,10 +19,10 @@ var downloadKongVars = kong.Vars{
 }
 
 type downloadCmd struct {
-	Arch       string `kong:"help=${download_arch_help},default=${download_arch_default}"`
-	OS         string `kong:"help=${download_os_help},default=${download_os_default}"`
+	Arch       string `kong:"help=${download_arch_help},default=${download_arch_default},predictor=arch"`
+	OS         string `kong:"help=${download_os_help},default=${download_os_default},predictor=os"`
 	Force      bool   `kong:"help=${download_force_help}"`
-	TargetFile string `kong:"required=true,arg,help=${download_target_file_help}"`
+	TargetFile string `kong:"required=true,arg,help=${download_target_file_help},predictor=binpath"`
 }
 
 func (d *downloadCmd) Run(*kong.Context) error {
diff --git a/cmd/bindown/main.go b/cmd/bindown/main.go
index 7bc5d92..22234da 100644
--- a/cmd/bindown/main.go
+++ b/cmd/bindown/main.go
@@ -1,12 +1,10 @@
 package main
 
 import (
-	"fmt"
 	"os"
-	"reflect"
-	"strings"
 
 	"github.com/alecthomas/kong"
+	"github.com/posener/complete"
 	"github.com/willabides/kongplete"
 )
 
@@ -21,33 +19,8 @@ var cli struct {
 	Version    versionCmd  `kong:"cmd"`
 	Download   downloadCmd `kong:"cmd,help=${download_help}"`
 	Config     configCmd   `kong:"cmd"`
-	Configfile string      `kong:"type=multipath,help=${configfile_help},default=${configfile_default},env='BINDOWN_CONFIG_FILE'"`
-	CellarDir  string      `kong:"type=path,help=${cellar_dir_help},env='BINDOWN_CELLAR'"`
-}
-
-func multipathMapper(ctx *kong.DecodeContext, target reflect.Value) error {
-	if target.Kind() != reflect.String {
-		return fmt.Errorf("\"multipath\" type must be applied to a string not %s", target.Type())
-	}
-	var path string
-	err := ctx.Scan.PopValueInto("file", &path)
-	if err != nil {
-		return err
-	}
-
-	for _, configFile := range strings.Split(path, "|") {
-		configFile = kong.ExpandPath(configFile)
-		stat, err := os.Stat(configFile)
-		if err != nil {
-			continue
-		}
-		if stat.IsDir() {
-			continue
-		}
-		target.SetString(configFile)
-		return nil
-	}
-	return fmt.Errorf("not found")
+	Configfile string      `kong:"type=multipath,help=${configfile_help},default=${configfile_default},env='BINDOWN_CONFIG_FILE',predictor=file"`
+	CellarDir  string      `kong:"type=path,help=${cellar_dir_help},env='BINDOWN_CELLAR',predictor=dir"`
 }
 
 func main() {
@@ -60,7 +33,16 @@ func main() {
 		kong.NamedMapper("multipath", kong.MapperFunc(multipathMapper)),
 	)
 
-	kongplete.Complete(parser)
+	kongplete.Complete(parser,
+		kongplete.WithPredictors(map[string]complete.Predictor{
+			"file":    complete.PredictFiles("*"),
+			"dir":     complete.PredictDirs("*"),
+			"binpath": binPathPredictor,
+			"arch":    archPredictor,
+			"os":      osPredictor,
+			"bin":     binPredictor,
+		}),
+	)
 
 	kongCtx, err := parser.Parse(os.Args[1:])
 	parser.FatalIfErrorf(err)
diff --git a/cmd/bindown/multipath.go b/cmd/bindown/multipath.go
new file mode 100644
index 0000000..1ddfa06
--- /dev/null
+++ b/cmd/bindown/multipath.go
@@ -0,0 +1,43 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"reflect"
+	"strings"
+
+	"github.com/alecthomas/kong"
+)
+
+func multipathMapper(ctx *kong.DecodeContext, target reflect.Value) error {
+	if target.Kind() != reflect.String {
+		return fmt.Errorf("\"multipath\" type must be applied to a string not %s", target.Type())
+	}
+	var path string
+	err := ctx.Scan.PopValueInto("file", &path)
+	if err != nil {
+		return err
+	}
+
+	existing := multifileFindExisting(path)
+	if existing == "" {
+		return fmt.Errorf("not found")
+	}
+	target.SetString(existing)
+	return nil
+}
+
+func multifileFindExisting(multiFile string) string {
+	for _, configFile := range strings.Split(multiFile, "|") {
+		configFile = kong.ExpandPath(configFile)
+		stat, err := os.Stat(configFile)
+		if err != nil {
+			continue
+		}
+		if stat.IsDir() {
+			continue
+		}
+		return configFile
+	}
+	return ""
+}
diff --git a/go.mod b/go.mod
index a8e4c1f..2648503 100644
--- a/go.mod
+++ b/go.mod
@@ -6,9 +6,10 @@ require (
 	github.com/alecthomas/kong v0.2.2
 	github.com/andybalholm/brotli v1.0.0 // indirect
 	github.com/frankban/quicktest v1.4.2 // indirect
+	github.com/killa-beez/gopkgs/sets/builtins v0.0.0-20191206232703-3018f97f77a9
 	github.com/mholt/archiver/v3 v3.3.0
-	github.com/mitchellh/mapstructure v1.1.2 // indirect
 	github.com/pierrec/lz4 v2.3.0+incompatible // indirect
+	github.com/posener/complete v1.2.3
 	github.com/stretchr/testify v1.4.0
 	github.com/udhos/equalfile v0.3.0
 	github.com/willabides/kongplete v0.0.0-20200218163413-c50671632cd8
diff --git a/go.sum b/go.sum
index bbf19ef..cdbedb4 100644
--- a/go.sum
+++ b/go.sum
@@ -1,5 +1,3 @@
-github.com/alecthomas/kong v0.2.1 h1:V1tLBhyQBC4rsbXbcOvm3GBaytJSwRNX69fp1WJxbqQ=
-github.com/alecthomas/kong v0.2.1/go.mod h1:+inYUSluD+p4L8KdviBSgzcqEjUQOfC5fQDRFuc36lI=
 github.com/alecthomas/kong v0.2.2 h1:sk9ucwuUP/T4+byYEdNU13ZNYzoQRML4IsrMbbUUKLk=
 github.com/alecthomas/kong v0.2.2/go.mod h1:kQOmtJgV+Lb4aj+I2LEn40cbtawdWJ9Y8QLq+lElKxE=
 github.com/andybalholm/brotli v0.0.0-20190621154722-5f990b63d2d6/go.mod h1:+lx6/Aqd1kLJ1GQfkvOnaZ1WGmLpMpbprPuIOOZX30U=
@@ -22,6 +20,8 @@ github.com/hashicorp/errwrap v1.0.0 h1:hLrqtEDnRye3+sgx6z4qVLNuviH3MR5aQ0ykNJa/U
 github.com/hashicorp/errwrap v1.0.0/go.mod h1:YH+1FKiLXxHSkmPseP+kNlulaMuP3n2brvKWEqk/Jc4=
 github.com/hashicorp/go-multierror v1.0.0 h1:iVjPR7a6H0tWELX5NxNe7bYopibicUzc7uPribsnS6o=
 github.com/hashicorp/go-multierror v1.0.0/go.mod h1:dHtQlpGsu+cZNNAkkCN/P3hoUDHhCYQXV3UM06sGGrk=
+github.com/killa-beez/gopkgs/sets/builtins v0.0.0-20191206232703-3018f97f77a9 h1:BStNA6fVmKPuDXvzJnZQQq++4FSoUYAxlJPH2J5UjNE=
+github.com/killa-beez/gopkgs/sets/builtins v0.0.0-20191206232703-3018f97f77a9/go.mod h1:ZP4kZV3WGKCESlO7hZkyyKM1Zprcf2FQ5rDq44f799M=
 github.com/klauspost/compress v1.4.1/go.mod h1:RyIbtBH6LamlWaDj8nUwkbUhJ87Yi3uG0guNDohfE1A=
 github.com/klauspost/compress v1.9.2 h1:LfVyl+ZlLlLDeQ/d2AqfGIIH4qEDu0Ed2S5GyhCWIWY=
 github.com/klauspost/compress v1.9.2/go.mod h1:RyIbtBH6LamlWaDj8nUwkbUhJ87Yi3uG0guNDohfE1A=
@@ -35,7 +35,6 @@ github.com/kr/text v0.1.0 h1:45sCR5RtlFHMR4UwH9sdQ5TC8v0qDQCHnXt+kaKSTVE=
 github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
 github.com/mholt/archiver/v3 v3.3.0 h1:vWjhY8SQp5yzM9P6OJ/eZEkmi3UAbRrxCq48MxjAzig=
 github.com/mholt/archiver/v3 v3.3.0/go.mod h1:YnQtqsp+94Rwd0D/rk5cnLrxusUBUXg+08Ebtr1Mqao=
-github.com/mitchellh/mapstructure v1.1.2/go.mod h1:FVVH3fgwuzCH5S8UJGiWEs2h04kUh9fWfEaFds41c1Y=
 github.com/nwaples/rardecode v1.0.0 h1:r7vGuS5akxOnR4JQSkko62RJ1ReCMXxQRPtxsiFMBOs=
 github.com/nwaples/rardecode v1.0.0/go.mod h1:5DzqNKiOdpKKBH87u8VlvAnPZMXcGRhxWkRpHbbfGS0=
 github.com/pierrec/lz4 v2.0.5+incompatible/go.mod h1:pdkljMzZIN41W+lC3N2tnIh5sFi+IEE17M5jbnwPHcY=