diff --git a/mcfg/cli.go b/mcfg/cli.go
index fcf2968..4393669 100644
--- a/mcfg/cli.go
+++ b/mcfg/cli.go
@@ -7,6 +7,8 @@ import (
 	"reflect"
 	"sort"
 	"strings"
+
+	"github.com/mediocregopher/mediocre-go-lib/merr"
 )
 
 // SourceCLI is a Source which will parse configuration from the CLI.
@@ -86,7 +88,8 @@ func (cli SourceCLI) Parse(params []Param) ([]ParamValue, error) {
 				break
 			}
 			if !pvOk {
-				return nil, fmt.Errorf("unexpected config parameter %q", arg)
+				err := merr.New("unexpected config parameter")
+				return nil, merr.WithValue(err, "param", arg, true)
 			}
 		}
 
@@ -114,7 +117,8 @@ func (cli SourceCLI) Parse(params []Param) ([]ParamValue, error) {
 		pvStrValOk = false
 	}
 	if pvOk && !pvStrValOk {
-		return nil, fmt.Errorf("param %q expected a value", key)
+		err := merr.New("param expected a value")
+		return nil, merr.WithValue(err, "param", key, true)
 	}
 	return pvs, nil
 }
@@ -140,6 +144,9 @@ func (cli SourceCLI) printHelp(w io.Writer, pM map[string]Param) {
 	}
 
 	sort.Slice(pA, func(i, j int) bool {
+		if pA[i].Required != pA[j].Required {
+			return pA[i].Required
+		}
 		return pA[i].arg < pA[j].arg
 	})
 
@@ -161,6 +168,8 @@ func (cli SourceCLI) printHelp(w io.Writer, pM map[string]Param) {
 		fmt.Fprintf(w, "\n%s", p.arg)
 		if p.IsBool {
 			fmt.Fprintf(w, " (Flag)")
+		} else if p.Required {
+			fmt.Fprintf(w, " (Required)")
 		} else if defVal := fmtDefaultVal(p.Into); defVal != "" {
 			fmt.Fprintf(w, " (Default: %s)", defVal)
 		}
diff --git a/mcfg/cli_test.go b/mcfg/cli_test.go
index e0f0114..b696687 100644
--- a/mcfg/cli_test.go
+++ b/mcfg/cli_test.go
@@ -18,7 +18,8 @@ func TestSourceCLIHelp(t *T) {
 	Int(ctx, "foo", 5, "Test int param")
 	Bool(ctx, "bar", "Test bool param")
 	String(ctx, "baz", "baz", "Test string param")
-	String(ctx, "baz2", "", "")
+	RequiredString(ctx, "baz2", "")
+	RequiredString(ctx, "baz3", "")
 	src := SourceCLI{}
 
 	buf := new(bytes.Buffer)
@@ -27,14 +28,16 @@ func TestSourceCLIHelp(t *T) {
 	SourceCLI{}.printHelp(buf, pM)
 
 	exp := `
+--baz2 (Required)
+
+--baz3 (Required)
+
 --bar (Flag)
 	Test bool param
 
 --baz (Default: "baz")
 	Test string param
 
---baz2
-
 --foo (Default: 5)
 	Test int param
 
diff --git a/mcfg/env.go b/mcfg/env.go
index dfe4cde..026fa49 100644
--- a/mcfg/env.go
+++ b/mcfg/env.go
@@ -1,9 +1,10 @@
 package mcfg
 
 import (
-	"fmt"
 	"os"
 	"strings"
+
+	"github.com/mediocregopher/mediocre-go-lib/merr"
 )
 
 // SourceEnv is a Source which will parse configuration from the process
@@ -56,7 +57,8 @@ func (env SourceEnv) Parse(params []Param) ([]ParamValue, error) {
 	for _, kv := range kvs {
 		split := strings.SplitN(kv, "=", 2)
 		if len(split) != 2 {
-			return nil, fmt.Errorf("malformed environment kv %q", kv)
+			err := merr.New("malformed environment key/value pair")
+			return nil, merr.WithValue(err, "kv", kv, true)
 		}
 		k, v := split[0], split[1]
 		if p, ok := pM[k]; ok {
diff --git a/mcfg/mcfg.go b/mcfg/mcfg.go
index 152e3d3..e63f5da 100644
--- a/mcfg/mcfg.go
+++ b/mcfg/mcfg.go
@@ -4,10 +4,10 @@ package mcfg
 
 import (
 	"encoding/json"
-	"fmt"
 	"sort"
 
 	"github.com/mediocregopher/mediocre-go-lib/mctx"
+	"github.com/mediocregopher/mediocre-go-lib/merr"
 )
 
 // TODO Sources:
@@ -97,7 +97,8 @@ func populate(params []Param, src Source) error {
 		if !param.Required {
 			continue
 		} else if _, ok := pvM[param.hash()]; !ok {
-			return fmt.Errorf("param %q is required", param.fullName())
+			err := merr.New("required parameter is not set")
+			return merr.WithValue(err, "param", param.fullName(), true)
 		}
 	}
 
diff --git a/mcfg/source.go b/mcfg/source.go
index 152f654..8c8717e 100644
--- a/mcfg/source.go
+++ b/mcfg/source.go
@@ -44,6 +44,7 @@ func (ss Sources) Parse(params []Param) ([]ParamValue, error) {
 // variables.
 type SourceMap map[string]string
 
+// Parse implements the method for the Source interface.
 func (m SourceMap) Parse(params []Param) ([]ParamValue, error) {
 	pvs := make([]ParamValue, 0, len(m))
 	for _, p := range params {