diff --git a/.changelog/15933.txt b/.changelog/15933.txt
new file mode 100644
index 000000000..fec161b08
--- /dev/null
+++ b/.changelog/15933.txt
@@ -0,0 +1,7 @@
+```release-note:improvement
+cli: Warn when variable key includes characters that require the use of the `index` function in templates
+```
+
+```release-note:improvement
+ui: Warn when variable key includes characters that require the use of the `index` function in templates
+```
diff --git a/command/job_validate.go b/command/job_validate.go
index 85031a1b0..8f234793a 100644
--- a/command/job_validate.go
+++ b/command/job_validate.go
@@ -8,6 +8,7 @@ import (
 	"github.com/hashicorp/go-multierror"
 	"github.com/hashicorp/nomad/api"
 	"github.com/hashicorp/nomad/command/agent"
+	"github.com/hashicorp/nomad/helper"
 	"github.com/hashicorp/nomad/helper/pointer"
 	"github.com/posener/complete"
 )
@@ -196,8 +197,7 @@ func (c *JobValidateCommand) Run(args []string) int {
 
 	// Print any warnings if there are any
 	if jr.Warnings != "" {
-		c.Ui.Output(
-			c.Colorize().Color(fmt.Sprintf("[bold][yellow]Job Warnings:\n%s[reset]\n", jr.Warnings)))
+		c.Ui.Output(c.FormatWarnings("Job", jr.Warnings))
 	}
 
 	// Done!
@@ -225,30 +225,6 @@ func (c *JobValidateCommand) validateLocal(aj *api.Job) (*api.JobValidateRespons
 		}
 	}
 
-	out.Warnings = mergeMultierrorWarnings(job.Warnings())
+	out.Warnings = helper.MergeMultierrorWarnings(job.Warnings())
 	return &out, nil
 }
-
-func mergeMultierrorWarnings(errs ...error) string {
-	if len(errs) == 0 {
-		return ""
-	}
-
-	var mErr multierror.Error
-	_ = multierror.Append(&mErr, errs...)
-
-	mErr.ErrorFormat = warningsFormatter
-
-	return mErr.Error()
-}
-
-func warningsFormatter(es []error) string {
-	sb := strings.Builder{}
-	sb.WriteString(fmt.Sprintf("%d warning(s):\n", len(es)))
-
-	for i := range es {
-		sb.WriteString(fmt.Sprintf("\n* %s", es[i]))
-	}
-
-	return sb.String()
-}
diff --git a/command/meta.go b/command/meta.go
index 736dfcfa2..aa2b505cb 100644
--- a/command/meta.go
+++ b/command/meta.go
@@ -2,6 +2,7 @@ package command
 
 import (
 	"flag"
+	"fmt"
 	"os"
 	"strings"
 
@@ -216,6 +217,15 @@ func (m *Meta) SetupUi(args []string) {
 	}
 }
 
+// FormatWarnings returns a string with the warnings formatted for CLI output.
+func (m *Meta) FormatWarnings(header string, warnings string) string {
+	return m.Colorize().Color(
+		fmt.Sprintf("[bold][yellow]%s Warnings:\n%s[reset]\n",
+			header,
+			warnings,
+		))
+}
+
 type usageOptsFlags uint8
 
 const (
diff --git a/command/var_put.go b/command/var_put.go
index fb19417d7..b979d6a47 100644
--- a/command/var_put.go
+++ b/command/var_put.go
@@ -7,8 +7,11 @@ import (
 	"io"
 	"os"
 	"path/filepath"
+	"regexp"
 	"strings"
 
+	multierror "github.com/hashicorp/go-multierror"
+	"github.com/hashicorp/go-set"
 	"github.com/hashicorp/hcl"
 	"github.com/hashicorp/hcl/hcl/ast"
 	"github.com/hashicorp/nomad/api"
@@ -16,8 +19,13 @@ import (
 	"github.com/mitchellh/cli"
 	"github.com/mitchellh/mapstructure"
 	"github.com/posener/complete"
+	"golang.org/x/exp/slices"
 )
 
+// Detect characters that are not valid identifiers to emit a warning when they
+// are used in as a variable key.
+var invalidIdentifier = regexp.MustCompile(`[^_\pN\pL]`)
+
 type VarPutCommand struct {
 	Meta
 
@@ -270,6 +278,7 @@ func (c *VarPutCommand) Run(args []string) int {
 		return 1
 	}
 
+	var warnings *multierror.Error
 	if len(args) > 0 {
 		data, err := parseArgsData(stdin, args)
 		if err != nil {
@@ -288,6 +297,9 @@ func (c *VarPutCommand) Run(args []string) int {
 				}
 				continue
 			}
+			if err := warnInvalidIdentifier(k); err != nil {
+				warnings = multierror.Append(warnings, err)
+			}
 			sv.Items[k] = vs
 		}
 	}
@@ -318,6 +330,13 @@ func (c *VarPutCommand) Run(args []string) int {
 	successMsg := fmt.Sprintf(
 		"Created variable %q with modify index %v", sv.Path, sv.ModifyIndex)
 
+	if warnings != nil {
+		c.Ui.Warn(c.FormatWarnings(
+			"Variable",
+			helper.MergeMultierrorWarnings(warnings),
+		))
+	}
+
 	var out string
 	switch c.outFmt {
 	case "json":
@@ -525,3 +544,33 @@ func (c *VarPutCommand) validateOutputFlag() error {
 		return errors.New(errInvalidOutFormat)
 	}
 }
+
+func warnInvalidIdentifier(in string) error {
+	invalid := invalidIdentifier.FindAllString(in, -1)
+	if len(invalid) == 0 {
+		return nil
+	}
+
+	// Use %s instead of %q to avoid escaping characters.
+	return fmt.Errorf(
+		`"%s" contains characters %s that require the 'index' function for direct access in templates`,
+		in,
+		formatInvalidVarKeyChars(invalid),
+	)
+}
+
+func formatInvalidVarKeyChars(invalid []string) string {
+	// Deduplicate characters
+	chars := set.From(invalid)
+
+	// Sort the characters for output
+	charList := make([]string, 0, chars.Size())
+	for _, k := range chars.List() {
+		// Use %s instead of %q to avoid escaping characters.
+		charList = append(charList, fmt.Sprintf(`"%s"`, k))
+	}
+	slices.Sort(charList)
+
+	// Build string
+	return fmt.Sprintf("[%s]", strings.Join(charList, ","))
+}
diff --git a/command/var_put_test.go b/command/var_put_test.go
index c5bcbb9ad..8daf14728 100644
--- a/command/var_put_test.go
+++ b/command/var_put_test.go
@@ -2,6 +2,8 @@ package command
 
 import (
 	"encoding/json"
+	"fmt"
+	"regexp"
 	"strings"
 	"testing"
 
@@ -9,6 +11,7 @@ import (
 	"github.com/hashicorp/nomad/ci"
 	"github.com/mitchellh/cli"
 	"github.com/posener/complete"
+	"github.com/shoenig/test/must"
 	"github.com/stretchr/testify/require"
 )
 
@@ -121,3 +124,116 @@ func TestVarPutCommand_AutocompleteArgs(t *testing.T) {
 	require.Equal(t, 1, len(res))
 	require.Equal(t, sv.Path, res[0])
 }
+
+func TestVarPutCommand_KeyWarning(t *testing.T) {
+	// Extract invalid characters from warning message.
+	r := regexp.MustCompile(`contains characters \[(.*)\]`)
+
+	tcs := []struct {
+		name     string
+		goodKeys []string
+		badKeys  []string
+		badChars []string
+	}{
+		{
+			name:     "simple",
+			goodKeys: []string{"simple"},
+		},
+		{
+			name:     "hasDot",
+			badKeys:  []string{"has.Dot"},
+			badChars: []string{`"."`},
+		},
+		{
+			name:     "unicode_letters",
+			goodKeys: []string{"世界"},
+		},
+		{
+			name:     "unicode_numbers",
+			goodKeys: []string{"٣٢١"},
+		},
+		{
+			name:     "two_good",
+			goodKeys: []string{"aardvark", "beagle"},
+		},
+		{
+			name:     "one_good_one_bad",
+			goodKeys: []string{"aardvark"},
+			badKeys:  []string{"bad.key"},
+			badChars: []string{`"."`},
+		},
+		{
+			name:     "one_good_two_bad",
+			goodKeys: []string{"aardvark"},
+			badKeys:  []string{"bad.key", "also-bad"},
+			badChars: []string{`"."`, `"-"`},
+		},
+		{
+			name:     "repeated_bad_char",
+			goodKeys: []string{"aardvark"},
+			badKeys:  []string{"bad.key", "also.bad"},
+			badChars: []string{`"."`, `"."`},
+		},
+		{
+			name:     "repeated_bad_char_same_key",
+			goodKeys: []string{"aardvark"},
+			badKeys:  []string{"bad.key."},
+			badChars: []string{`"."`},
+		},
+		{
+			name:     "dont_escape",
+			goodKeys: []string{"aardvark"},
+			badKeys:  []string{"bad\\key"},
+			badChars: []string{`"\"`},
+		},
+	}
+
+	ci.Parallel(t)
+	_, _, url := testServer(t, false, nil)
+
+	for _, tc := range tcs {
+		t.Run(tc.name, func(t *testing.T) {
+			tc := tc       // capture test case
+			ci.Parallel(t) // make the subtests parallel
+
+			keys := append(tc.goodKeys, tc.badKeys...) // combine keys into a single slice
+			for i, k := range keys {
+				keys[i] = k + "=value" // Make each key into a k=v pair; value is not part of test
+			}
+
+			ui := cli.NewMockUi()
+			cmd := &VarPutCommand{Meta: Meta{Ui: ui}}
+			args := append([]string{"-address=" + url, "-force", "-out=json", "test/var"}, keys...)
+			code := cmd.Run(args)
+			errOut := ui.ErrorWriter.String()
+
+			must.Eq(t, 0, code) // the command should always succeed
+
+			badKeysLen := len(tc.badKeys)
+			switch badKeysLen {
+			case 0:
+				must.Eq(t, "", errOut) // cases with no bad keys shouldn't put anything to stderr
+				return
+			case 1:
+				must.StrContains(t, errOut, "1 warning:") // header should be singular
+			default:
+				must.StrContains(t, errOut, fmt.Sprintf("%d warnings:", badKeysLen)) // header should be plural
+			}
+
+			for _, k := range tc.badKeys {
+				must.StrContains(t, errOut, k) // every bad key should appear in the warning output
+			}
+
+			if len(tc.badChars) > 0 {
+				invalid := r.FindAllStringSubmatch(errOut, -1)
+				for i, k := range tc.badChars {
+					must.Eq(t, invalid[i][1], k) // every bad char should appear in the warning output
+				}
+			}
+
+			for _, k := range tc.goodKeys {
+				must.StrNotContains(t, errOut, k) // good keys should not be emitted
+			}
+		})
+	}
+}
diff --git a/helper/warning.go b/helper/warning.go
new file mode 100644
index 000000000..b5733794b
--- /dev/null
+++ b/helper/warning.go
@@ -0,0 +1,42 @@
+package helper
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/hashicorp/go-multierror"
+)
+
+// MergeMultierrorWarnings takes warnings and merges them into a returnable
+// string. This method is used to return API and CLI errors.
+func MergeMultierrorWarnings(errs ...error) string {
+	if len(errs) == 0 {
+		return ""
+	}
+
+	var mErr multierror.Error
+	_ = multierror.Append(&mErr, errs...)
+	mErr.ErrorFormat = warningsFormatter
+
+	return mErr.Error()
+}
+
+// warningsFormatter is used to format warnings.
+func warningsFormatter(es []error) string {
+	sb := strings.Builder{}
+
+	switch len(es) {
+	case 0:
+		return ""
+	case 1:
+		sb.WriteString("1 warning:\n")
+	default:
+		sb.WriteString(fmt.Sprintf("%d warnings:\n", len(es)))
+	}
+
+	for _, err := range es {
+		sb.WriteString(fmt.Sprintf("\n* %s", strings.TrimSpace(err.Error())))
+	}
+
+	return sb.String()
+}
diff --git a/helper/warning_test.go b/helper/warning_test.go
new file mode 100644
index 000000000..703ede350
--- /dev/null
+++ b/helper/warning_test.go
@@ -0,0 +1,54 @@
+package helper
+
+import (
+	"errors"
+	"strings"
+	"testing"
+
+	"github.com/hashicorp/nomad/ci"
+	"github.com/shoenig/test/must"
+)
+
+func TestMergeMultierrorWarnings(t *testing.T) {
+	ci.Parallel(t)
+
+	testCases := []struct {
+		name     string
+		errs     []error
+		expected string
+	}{
+		{
+			name:     "no warning",
+			errs:     []error{},
+			expected: "",
+		},
+		{
+			name: "single warning",
+			errs: []error{
+				errors.New("warning"),
+			},
+			expected: `
+1 warning:
+
+* warning`,
+		},
+		{
+			name: "multiple warnings",
+			errs: []error{
+				errors.New("warning 1"),
+				errors.New("warning 2"),
+			},
+			expected: `
+2 warnings:
+
+* warning 1
+* warning 2`,
+		},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			got := MergeMultierrorWarnings(tc.errs...)
+			must.Eq(t, got, strings.TrimSpace(tc.expected))
+		})
+	}
+}
diff --git a/nomad/job_endpoint.go b/nomad/job_endpoint.go
index 1376d9c77..3626cee24 100644
--- a/nomad/job_endpoint.go
+++ b/nomad/job_endpoint.go
@@ -122,7 +122,7 @@ func (j *Job) Register(args *structs.JobRegisterRequest, reply *structs.JobRegis
 	}
 
 	// Set the warning message
-	reply.Warnings = structs.MergeMultierrorWarnings(warnings...)
+	reply.Warnings = helper.MergeMultierrorWarnings(warnings...)
 
 	// Check job submission permissions
 	aclObj, err := j.srv.ResolveACL(args)
@@ -292,7 +292,7 @@ func (j *Job) Register(args *structs.JobRegisterRequest, reply *structs.JobRegis
 	}
 	if policyWarnings != nil {
 		warnings = append(warnings, policyWarnings)
-		reply.Warnings = structs.MergeMultierrorWarnings(warnings...)
+		reply.Warnings = helper.MergeMultierrorWarnings(warnings...)
 	}
 
 	// Clear the Vault token
@@ -586,7 +586,7 @@ func (j *Job) Validate(args *structs.JobValidateRequest, reply *structs.JobValid
 	validateWarnings = append(validateWarnings, mutateWarnings...)
 
 	// Set the warning message
-	reply.Warnings = structs.MergeMultierrorWarnings(validateWarnings...)
+	reply.Warnings = helper.MergeMultierrorWarnings(validateWarnings...)
 	reply.DriverConfigValidated = true
 	return nil
 }
@@ -1711,7 +1711,7 @@ func (j *Job) Plan(args *structs.JobPlanRequest, reply *structs.JobPlanResponse)
 	args.Job = job
 
 	// Set the warning message
-	reply.Warnings = structs.MergeMultierrorWarnings(warnings...)
+	reply.Warnings = helper.MergeMultierrorWarnings(warnings...)
 
 	// Check job submission permissions, which we assume is the same for plan
 	if aclObj, err := j.srv.ResolveACL(args); err != nil {
@@ -1749,7 +1749,7 @@ func (j *Job) Plan(args *structs.JobPlanRequest, reply *structs.JobPlanResponse)
 	}
 	if policyWarnings != nil {
 		warnings = append(warnings, policyWarnings)
-		reply.Warnings = structs.MergeMultierrorWarnings(warnings...)
+		reply.Warnings = helper.MergeMultierrorWarnings(warnings...)
 	}
 
 	// Interpolate the job for this region
diff --git a/nomad/structs/funcs.go b/nomad/structs/funcs.go
index 89c6d84b2..9e497925a 100644
--- a/nomad/structs/funcs.go
+++ b/nomad/structs/funcs.go
@@ -10,38 +10,11 @@ import (
 	"strconv"
 	"strings"
 
-	"github.com/hashicorp/go-multierror"
 	"github.com/hashicorp/go-set"
 	"github.com/hashicorp/nomad/acl"
 	"golang.org/x/crypto/blake2b"
 )
 
-// MergeMultierrorWarnings takes job warnings and canonicalize warnings and
-// merges them into a returnable string. Both the errors may be nil.
-func MergeMultierrorWarnings(errs ...error) string {
-	if len(errs) == 0 {
-		return ""
-	}
-
-	var mErr multierror.Error
-	_ = multierror.Append(&mErr, errs...)
-	mErr.ErrorFormat = warningsFormatter
-
-	return mErr.Error()
-}
-
-// warningsFormatter is used to format job warnings
-func warningsFormatter(es []error) string {
-	sb := strings.Builder{}
-	sb.WriteString(fmt.Sprintf("%d warning(s):\n", len(es)))
-
-	for i := range es {
-		sb.WriteString(fmt.Sprintf("\n* %s", es[i]))
-	}
-
-	return sb.String()
-}
-
 // RemoveAllocs is used to remove any allocs with the given IDs
 // from the list of allocations
 func RemoveAllocs(allocs []*Allocation, remove []*Allocation) []*Allocation {
diff --git a/nomad/structs/funcs_test.go b/nomad/structs/funcs_test.go
index ec4cbe139..a1a612edd 100644
--- a/nomad/structs/funcs_test.go
+++ b/nomad/structs/funcs_test.go
@@ -2,7 +2,6 @@ package structs
 
 import (
 	"encoding/base64"
-	"errors"
 	"fmt"
 	"testing"
 
@@ -1062,27 +1061,6 @@ func TestGenerateMigrateToken(t *testing.T) {
 	assert.True(CompareMigrateToken("x", nodeSecret, token2))
 }
 
-func TestMergeMultierrorWarnings(t *testing.T) {
-	ci.Parallel(t)
-
-	var errs []error
-
-	// empty
-	str := MergeMultierrorWarnings(errs...)
-	require.Equal(t, "", str)
-
-	// non-empty
-	errs = []error{
-		errors.New("foo"),
-		nil,
-		errors.New("bar"),
-	}
-
-	str = MergeMultierrorWarnings(errs...)
-
-	require.Equal(t, "2 warning(s):\n\n* foo\n* bar", str)
-}
-
 func TestVaultPoliciesSet(t *testing.T) {
 	input := map[string]map[string]*Vault{
 		"tg1": {
diff --git a/ui/app/components/variable-form.js b/ui/app/components/variable-form.js
index 62373fd2a..0ac54bf8b 100644
--- a/ui/app/components/variable-form.js
+++ b/ui/app/components/variable-form.js
@@ -20,6 +20,9 @@ const EMPTY_KV = {
   warnings: EmberObject.create(),
 };
 
+// Capture characters that are not _, letters, or numbers using Unicode.
+const invalidKeyCharactersRegex = new RegExp(/[^_\p{Letter}\p{Number}]/gu);
+
 export default class VariableFormComponent extends Component {
   @service flashMessages;
   @service router;
@@ -146,9 +149,16 @@ export default class VariableFormComponent extends Component {
   @action
   validateKey(entry, e) {
     const value = e.target.value;
-    // No dots in key names
-    if (value.includes('.')) {
-      entry.warnings.set('dottedKeyError', 'Key should not contain a period.');
+    // Only letters, numbers, and _ are allowed in keys
+    const invalidChars = value.match(invalidKeyCharactersRegex);
+    if (invalidChars) {
+      const invalidCharsOuput = [...new Set(invalidChars)]
+        .sort()
+        .map((c) => `'${c}'`);
+      entry.warnings.set(
+        'dottedKeyError',
+        `${value} contains characters [${invalidCharsOuput}] that require the "index" function for direct access in templates.`
+      );
     } else {
       delete entry.warnings.dottedKeyError;
       entry.warnings.notifyPropertyChange('dottedKeyError');
diff --git a/ui/tests/integration/components/variable-form-test.js b/ui/tests/integration/components/variable-form-test.js
index 627b2cf1a..329942b55 100644
--- a/ui/tests/integration/components/variable-form-test.js
+++ b/ui/tests/integration/components/variable-form-test.js
@@ -280,15 +280,52 @@ module('Integration | Component | variable-form', function (hooks) {
         })
       );
 
-      await render(hbs`<VariableForm @model={{this.mockedModel}} />`);
-
-      await typeIn('.key-value label:nth-child(1) input', 'superSecret');
-      assert.dom('.key-value-error').doesNotExist();
-
-      find('.key-value label:nth-child(1) input').value = '';
-
-      await typeIn('.key-value label:nth-child(1) input', 'super.secret');
-      assert.dom('.key-value-error').exists();
+      const testCases = [
+        {
+          name: 'valid key',
+          key: 'superSecret2',
+          warn: false,
+        },
+        {
+          name: 'invalid key with dot',
+          key: 'super.secret',
+          warn: true,
+        },
+        {
+          name: 'invalid key with slash',
+          key: 'super/secret',
+          warn: true,
+        },
+        {
+          name: 'invalid key with emoji',
+          key: 'supersecretspy🕵️',
+          warn: true,
+        },
+        {
+          name: 'unicode letters',
+          key: '世界',
+          warn: false,
+        },
+        {
+          name: 'unicode numbers',
+          key: '٣٢١',
+          warn: false,
+        },
+        {
+          name: 'unicode letters and numbers',
+          key: '世٢界١',
+          warn: false,
+        },
+      ];
+      for (const tc of testCases) {
+        await render(hbs`<VariableForm @model={{this.mockedModel}} />`);
+        await typeIn('[data-test-var-key]', tc.key);
+        if (tc.warn) {
+          assert.dom('.key-value-error').exists(tc.name);
+        } else {
+          assert.dom('.key-value-error').doesNotExist(tc.name);
+        }
+      }
     });
 
     test('warns you when you create a duplicate key', async function (assert) {