diff --git a/completers/nix-build_completer/cmd/root.go b/completers/nix-build_completer/cmd/root.go
new file mode 100644
index 00000000..544f0c3c
--- /dev/null
+++ b/completers/nix-build_completer/cmd/root.go
@@ -0,0 +1,43 @@
+package cmd
+
+import (
+	"github.com/rsteube/carapace"
+	"github.com/rsteube/carapace-bin/pkg/actions/tools/nix"
+	"github.com/spf13/cobra"
+)
+
+var rootCmd = &cobra.Command{
+	Use:   "nix-build",
+	Short: "build a Nix expression",
+	Long:  "https://nixos.org/manual/nix/stable/command-ref/nix-build.html",
+	Run:   func(cmd *cobra.Command, args []string) {},
+}
+
+func Execute() error {
+	return rootCmd.Execute()
+}
+func init() {
+	carapace.Gen(rootCmd).Standalone()
+
+	rootCmd.Flags().StringP("attr", "A", "", "Attribute to build")
+	rootCmd.Flags().Bool("dry-run", false, "Show what store paths would be built or downloaded")
+	rootCmd.Flags().StringP("include", "I", "", "Include paths")
+	rootCmd.Flags().Bool("no-out-link", false, "Do not create a symlink to the output path")
+	rootCmd.Flags().StringP("out-link", "o", "", "Change the name of the symlink to the output path")
+	// TODO support --arg and --argstr
+
+	carapace.Gen(rootCmd).FlagCompletion(carapace.ActionMap{
+		"attr": carapace.ActionCallback(func(c carapace.Context) carapace.Action {
+			opts := nix.AttributeOpts{Source: "default.nix", Include: rootCmd.Flag("include").Value.String()}
+			if len(c.Args) > 0 {
+				opts.Source = c.Args[0]
+			}
+			return nix.ActionAttributes(opts)
+		}),
+	})
+
+	carapace.Gen(rootCmd).PositionalAnyCompletion(
+		nix.ActionPaths(),
+	)
+
+}
diff --git a/completers/nix-build_completer/main.go b/completers/nix-build_completer/main.go
new file mode 100644
index 00000000..a733fad2
--- /dev/null
+++ b/completers/nix-build_completer/main.go
@@ -0,0 +1,7 @@
+package main
+
+import "github.com/rsteube/carapace-bin/completers/nix-build_completer/cmd"
+
+func main() {
+	cmd.Execute()
+}
diff --git a/completers/nix-channel_completer/cmd/root.go b/completers/nix-channel_completer/cmd/root.go
index 4da5434f..1fd1ba5d 100644
--- a/completers/nix-channel_completer/cmd/root.go
+++ b/completers/nix-channel_completer/cmd/root.go
@@ -34,7 +34,7 @@ func init() {
 			} else if rootCmd.Flag("add").Changed {
 				switch len(c.Args) {
 				case 0:
-					return nix.ActionRemoteChannels()
+					return nix.ActionRemoteChannels().Invoke(c).Prefix("https://nixos.org/channels/").ToA()
 				case 1:
 					return nix.ActionLocalChannels()
 				}
diff --git a/pkg/actions/tools/nix/attribute.go b/pkg/actions/tools/nix/attribute.go
new file mode 100644
index 00000000..188d0820
--- /dev/null
+++ b/pkg/actions/tools/nix/attribute.go
@@ -0,0 +1,89 @@
+package nix
+
+import (
+	_ "embed"
+	"encoding/json"
+	"fmt"
+	"path"
+	"strings"
+
+	"github.com/rsteube/carapace"
+)
+
+//go:embed attributeComplete.nix
+var attributeCompleteScript string
+
+type AttributeOpts struct {
+	Source  string
+	Include string
+}
+
+// ActionAttributes completes attributes
+//
+//	firefox
+//	git
+func ActionAttributes(opts AttributeOpts) carapace.Action {
+	return carapace.ActionCallback(func(c carapace.Context) carapace.Action {
+		if opts.Source == "" {
+			opts.Source = "default.nix"
+		}
+
+		attrPath := c.CallbackValue
+
+		if strings.HasPrefix(opts.Source, "<") {
+			// expression is a local channel, use as-is
+		} else if strings.HasPrefix(opts.Source, "http:") || strings.HasPrefix(opts.Source, "https:") {
+			// expression is a url, wrap in fetchTarball
+			opts.Source = fmt.Sprintf("(fetchTarball %s)", opts.Source)
+		} else if strings.HasPrefix(opts.Source, "channel:") {
+			// expression is a channel alias, convert to url
+			channelName := opts.Source[8:]
+			opts.Source = fmt.Sprintf("(fetchTarball https://nixos.org/channels/%s/nixexprs.tar.xz)", channelName)
+		} else {
+			// expression is a local file
+			filePath := path.Clean(opts.Source)
+			if path.Base(filePath) == filePath {
+				// paths must have at least one `/`
+				filePath = fmt.Sprintf("./%s", filePath)
+			}
+			opts.Source = filePath
+		}
+		expression := fmt.Sprintf("import %s", opts.Source)
+
+		// nix itself handles quotes weirdly so we just avoid them altogether
+		if strings.Contains(attrPath, "\"") {
+			return carapace.ActionMessage("attrPath may not contain double-quotes")
+		}
+
+		// strip right-most attr
+		lastDotIndex := strings.LastIndex(attrPath, ".")
+		if lastDotIndex >= 0 {
+			attrPath = attrPath[0:lastDotIndex]
+		} else {
+			attrPath = ""
+		}
+
+		args := []string{
+			"--eval", "--json",
+			"--expr", attributeCompleteScript,
+			"--arg", "__carapaceInput__", expression,
+			"--argstr", "__carapaceAttrPath__", attrPath,
+		}
+		if opts.Include != "" {
+			args = append(args, "-I", opts.Include)
+		}
+		// TODO handle passing through --arg and --argstr from original command
+
+		return carapace.ActionExecCommand("nix-instantiate", args...)(func(output []byte) carapace.Action {
+			var data []string
+			json.Unmarshal(output, &data)
+
+			prefix := ""
+			if attrPath != "" {
+				prefix = fmt.Sprintf("%s.", attrPath)
+			}
+
+			return carapace.ActionValues(data...).Prefix(prefix).NoSpace()
+		})
+	})
+}
diff --git a/pkg/actions/tools/nix/attributeComplete.nix b/pkg/actions/tools/nix/attributeComplete.nix
new file mode 100644
index 00000000..4f98d858
--- /dev/null
+++ b/pkg/actions/tools/nix/attributeComplete.nix
@@ -0,0 +1,25 @@
+all@{ __carapaceInput__, __carapaceAttrPath__, ... }:
+let
+  inputArgs = builtins.removeAttrs all ["__carapaceInput__" "__carapaceAttrPath__"];
+
+  input =
+    if builtins.isFunction __carapaceInput__ then
+      __carapaceInput__ inputArgs
+    else
+      __carapaceInput__;
+
+  autocall = fnOrAttrset:
+    if builtins.isFunction fnOrAttrset then
+      fnOrAttrset {}
+    else
+      fnOrAttrset;
+
+  paths = builtins.filter (path: (builtins.isString path) && path != "") (builtins.split "\\." __carapaceAttrPath__);
+
+  reducer = attrset: name: autocall (builtins.getAttr name attrset);
+  result = builtins.foldl' reducer input paths;
+in
+  if builtins.isAttrs result then
+    builtins.attrNames result
+  else
+    []
diff --git a/pkg/actions/tools/nix/channel.go b/pkg/actions/tools/nix/channel.go
index 930da5a9..62c5ffd4 100644
--- a/pkg/actions/tools/nix/channel.go
+++ b/pkg/actions/tools/nix/channel.go
@@ -63,8 +63,6 @@ func ActionRemoteChannels() carapace.Action {
 		for _, result := range response.Data.Result {
 			vals = append(vals, result.Metric.Channel, result.Metric.Status, styleForStatus(result.Metric.Status))
 		}
-		return carapace.ActionCallback(func(c carapace.Context) carapace.Action {
-			return carapace.ActionStyledValuesDescribed(vals...).Invoke(c).Prefix("https://nixos.org/channels/").ToA()
-		})
+		return carapace.ActionStyledValuesDescribed(vals...)
 	})
 }
diff --git a/pkg/actions/tools/nix/path.go b/pkg/actions/tools/nix/path.go
new file mode 100644
index 00000000..1bacd46c
--- /dev/null
+++ b/pkg/actions/tools/nix/path.go
@@ -0,0 +1,31 @@
+package nix
+
+import (
+	"strings"
+
+	"github.com/rsteube/carapace"
+)
+
+// ActionPaths completes paths
+//
+// A path can be one of:
+//   - a local file path (default.nix)
+//   - an http/https URL (https://releases.nixos.org/../nixexprs.tar.xz
+//   - a channel: specifier (channel:nixos-22.05)
+//   - a local channel (<nixpkgs>)
+func ActionPaths() carapace.Action {
+	return carapace.ActionCallback(func(c carapace.Context) carapace.Action {
+		batch := carapace.Batch(
+			ActionLocalChannels().Prefix("<").Suffix(">"),
+			carapace.ActionFiles(),
+		)
+
+		if !strings.HasPrefix(c.CallbackValue, "channel:") {
+			batch = append(batch, carapace.ActionValues("channel:").NoSpace())
+		} else {
+			batch = append(batch, ActionRemoteChannels().Prefix("channel:"))
+		}
+
+		return batch.ToA()
+	})
+}