diff --git a/cmd/bkl/main.go b/cmd/bkl/main.go
index a68f061..8c03cb8 100644
--- a/cmd/bkl/main.go
+++ b/cmd/bkl/main.go
@@ -10,13 +10,13 @@ import (
 )
 
 type options struct {
-	OutputPath   *string `short:"o" long:"output" description:"output file path"`
-	OutputFormat *string `short:"f" long:"format" description:"output format"`
-	SkipParent   bool    `short:"P" long:"skip-parent" description:"skip loading parent templates"`
-	Verbose      bool    `short:"v" long:"verbose" description:"enable verbose logging"`
+	OutputPath   *flags.Filename `short:"o" long:"output" description:"output file path"`
+	OutputFormat *string         `short:"f" long:"format" description:"output format" choice:"json" choice:"json-pretty" choice:"toml" choice:"yaml"`
+	SkipParent   bool            `short:"P" long:"skip-parent" description:"skip loading parent templates"`
+	Verbose      bool            `short:"v" long:"verbose" description:"enable verbose logging"`
 
 	Positional struct {
-		InputPaths []string `positional-arg-name:"inputPath" required:"1" description:"input file path"`
+		InputPaths []flags.Filename `positional-arg-name:"inputPath" required:"1" description:"input file path"`
 	} `positional-args:"yes"`
 }
 
@@ -68,7 +68,7 @@ Related tools:
 			fileP.SetDebug(true)
 		}
 
-		realPath, f, err := bkl.FileMatch(path)
+		realPath, f, err := bkl.FileMatch(string(path))
 		if err != nil {
 			fatal(err)
 		}
@@ -96,7 +96,7 @@ Related tools:
 	if opts.OutputPath == nil {
 		err = p.OutputToWriter(os.Stdout, format)
 	} else {
-		err = p.OutputToFile(*opts.OutputPath, format)
+		err = p.OutputToFile(string(*opts.OutputPath), format)
 	}
 
 	if err != nil {
diff --git a/cmd/bklb/main.go b/cmd/bklb/main.go
index a44dc83..e5c2d9b 100644
--- a/cmd/bklb/main.go
+++ b/cmd/bklb/main.go
@@ -29,10 +29,11 @@ func main() {
 
 	if cmd == "bkl" {
 		// Run as bklb, not via symlink
+		//nolint:goerr113,revive,stylecheck
 		fatal(fmt.Errorf(`Usage:
   ln -s $(which bklb) toolb  # bklb will run 'tool'
 
-See https://bkl.gopatchy.io/#bklb for detailed documentation.`)) //nolint:goerr113
+See https://bkl.gopatchy.io/#bklb for detailed documentation.`))
 	}
 
 	cmdPath, err := exec.LookPath(cmd)
diff --git a/cmd/bkld/main.go b/cmd/bkld/main.go
index 9f92909..4fdeb25 100644
--- a/cmd/bkld/main.go
+++ b/cmd/bkld/main.go
@@ -12,12 +12,12 @@ import (
 )
 
 type options struct {
-	OutputPath   *string `short:"o" long:"output" description:"output file path"`
-	OutputFormat *string `short:"f" long:"format" description:"output format"`
+	OutputPath   *flags.Filename `short:"o" long:"output" description:"output file path"`
+	OutputFormat *string         `short:"f" long:"format" description:"output format" choice:"json" choice:"json-pretty" choice:"toml" choice:"yaml"`
 
 	Positional struct {
-		BasePath   string `positional-arg-name:"basePath" required:"true" description:"base layer file path"`
-		TargetPath string `positional-arg-name:"targetPath" required:"true" description:"target output file path"`
+		BasePath   flags.Filename `positional-arg-name:"basePath" required:"true" description:"base layer file path"`
+		TargetPath flags.Filename `positional-arg-name:"targetPath" required:"true" description:"target output file path"`
 	} `positional-args:"yes"`
 }
 
@@ -52,13 +52,13 @@ See https://bkl.gopatchy.io/#bkld for detailed documentation.`
 	}
 
 	if format == "" && opts.OutputPath != nil {
-		format = strings.TrimPrefix(filepath.Ext(*opts.OutputPath), ".")
+		format = strings.TrimPrefix(filepath.Ext(string(*opts.OutputPath)), ".")
 	}
 
 	bs := []*bkl.Parser{}
 	numDocs := 0
 
-	for _, path := range []string{opts.Positional.BasePath, opts.Positional.TargetPath} {
+	for _, path := range []string{string(opts.Positional.BasePath), string(opts.Positional.TargetPath)} {
 		realPath, f, err := bkl.FileMatch(path)
 		if err != nil {
 			fatal(err)
@@ -131,7 +131,7 @@ See https://bkl.gopatchy.io/#bkld for detailed documentation.`
 	fh := os.Stdout
 
 	if opts.OutputPath != nil {
-		fh, err = os.OpenFile(*opts.OutputPath, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0644)
+		fh, err = os.OpenFile(string(*opts.OutputPath), os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0644)
 		if err != nil {
 			fatal(err)
 		}
diff --git a/cmd/bkli/main.go b/cmd/bkli/main.go
index 8ef6031..e3d4f5d 100644
--- a/cmd/bkli/main.go
+++ b/cmd/bkli/main.go
@@ -12,11 +12,11 @@ import (
 )
 
 type options struct {
-	OutputPath   *string `short:"o" long:"output" description:"output file path"`
-	OutputFormat *string `short:"f" long:"format" description:"output format"`
+	OutputPath   *flags.Filename `short:"o" long:"output" description:"output file path"`
+	OutputFormat *string         `short:"f" long:"format" description:"output format"  choice:"json" choice:"json-pretty" choice:"toml" choice:"yaml"`
 
 	Positional struct {
-		InputPaths []string `positional-arg-name:"targetPath" required:"2" description:"target output file path"`
+		InputPaths []flags.Filename `positional-arg-name:"targetPath" required:"2" description:"target output file path"`
 	} `positional-args:"yes"`
 }
 
@@ -51,13 +51,13 @@ See https://bkl.gopatchy.io/#bkli for detailed documentation.`
 	}
 
 	if format == "" && opts.OutputPath != nil {
-		format = strings.TrimPrefix(filepath.Ext(*opts.OutputPath), ".")
+		format = strings.TrimPrefix(filepath.Ext(string(*opts.OutputPath)), ".")
 	}
 
 	var docs []any
 
 	for p, path := range opts.Positional.InputPaths {
-		realPath, f, err := bkl.FileMatch(path)
+		realPath, f, err := bkl.FileMatch(string(path))
 		if err != nil {
 			fatal(err)
 		}
@@ -108,7 +108,7 @@ See https://bkl.gopatchy.io/#bkli for detailed documentation.`
 	fh := os.Stdout
 
 	if opts.OutputPath != nil {
-		fh, err = os.OpenFile(*opts.OutputPath, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0644)
+		fh, err = os.OpenFile(string(*opts.OutputPath), os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0644)
 		if err != nil {
 			fatal(err)
 		}
diff --git a/cmd/bklr/main.go b/cmd/bklr/main.go
index ccb9cc4..3c2a586 100644
--- a/cmd/bklr/main.go
+++ b/cmd/bklr/main.go
@@ -12,11 +12,11 @@ import (
 )
 
 type options struct {
-	OutputPath   *string `short:"o" long:"output" description:"output file path"`
-	OutputFormat *string `short:"f" long:"format" description:"output format"`
+	OutputPath   *flags.Filename `short:"o" long:"output" description:"output file path"`
+	OutputFormat *string         `short:"f" long:"format" description:"output format" choice:"json" choice:"json-pretty" choice:"toml" choice:"yaml"`
 
 	Positional struct {
-		InputPath string `positional-arg-name:"layerPath" required:"true" description:"lower layer file path"`
+		InputPath flags.Filename `positional-arg-name:"layerPath" required:"true" description:"lower layer file path"`
 	} `positional-args:"yes"`
 }
 
@@ -44,7 +44,7 @@ See https://bkl.gopatchy.io/#bklr for detailed documentation.`
 		os.Exit(1)
 	}
 
-	realPath, format, err := bkl.FileMatch(opts.Positional.InputPath)
+	realPath, format, err := bkl.FileMatch(string(opts.Positional.InputPath))
 	if err != nil {
 		fatal(err)
 	}
@@ -57,7 +57,7 @@ See https://bkl.gopatchy.io/#bklr for detailed documentation.`
 	}
 
 	if opts.OutputPath != nil {
-		format = strings.TrimPrefix(filepath.Ext(*opts.OutputPath), ".")
+		format = strings.TrimPrefix(filepath.Ext(string(*opts.OutputPath)), ".")
 	}
 
 	if opts.OutputFormat != nil {
@@ -93,7 +93,7 @@ See https://bkl.gopatchy.io/#bklr for detailed documentation.`
 	fh := os.Stdout
 
 	if opts.OutputPath != nil {
-		fh, err = os.OpenFile(*opts.OutputPath, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0644)
+		fh, err = os.OpenFile(string(*opts.OutputPath), os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0644)
 		if err != nil {
 			fatal(err)
 		}