diff --git a/packages/tailwindcss-language-server/tests/code-actions/conflict.json b/packages/tailwindcss-language-server/tests/code-actions/conflict.json
index eccb1446..bd7fc028 100644
--- a/packages/tailwindcss-language-server/tests/code-actions/conflict.json
+++ b/packages/tailwindcss-language-server/tests/code-actions/conflict.json
@@ -7,6 +7,7 @@
       "diagnostics": [
         {
           "code": "cssConflict",
+          "source": "tailwindcss",
           "className": {
             "className": "lowercase",
             "classList": {
@@ -85,6 +86,7 @@
       "diagnostics": [
         {
           "code": "cssConflict",
+          "source": "tailwindcss",
           "className": {
             "className": "uppercase",
             "classList": {
diff --git a/packages/tailwindcss-language-server/tests/code-actions/invalid-screen.json b/packages/tailwindcss-language-server/tests/code-actions/invalid-screen.json
index 9c49c1b9..2b5b5364 100644
--- a/packages/tailwindcss-language-server/tests/code-actions/invalid-screen.json
+++ b/packages/tailwindcss-language-server/tests/code-actions/invalid-screen.json
@@ -8,6 +8,7 @@
       "diagnostics": [
         {
           "code": "invalidScreen",
+          "source": "tailwindcss",
           "range": {
             "start": { "line": 0, "character": 8 },
             "end": { "line": 0, "character": 13 }
diff --git a/packages/tailwindcss-language-server/tests/code-actions/invalid-theme.json b/packages/tailwindcss-language-server/tests/code-actions/invalid-theme.json
index 7aceb38e..958ecf0d 100644
--- a/packages/tailwindcss-language-server/tests/code-actions/invalid-theme.json
+++ b/packages/tailwindcss-language-server/tests/code-actions/invalid-theme.json
@@ -8,6 +8,7 @@
       "diagnostics": [
         {
           "code": "invalidConfigPath",
+          "source": "tailwindcss",
           "range": {
             "start": { "line": 0, "character": 21 },
             "end": { "line": 0, "character": 35 }
diff --git a/packages/tailwindcss-language-server/tests/code-actions/invalid-variant.json b/packages/tailwindcss-language-server/tests/code-actions/invalid-variant.json
index 5fbd5a7a..20bd2f36 100644
--- a/packages/tailwindcss-language-server/tests/code-actions/invalid-variant.json
+++ b/packages/tailwindcss-language-server/tests/code-actions/invalid-variant.json
@@ -8,6 +8,7 @@
       "diagnostics": [
         {
           "code": "invalidVariant",
+          "source": "tailwindcss",
           "range": {
             "start": { "line": 0, "character": 10 },
             "end": { "line": 0, "character": 16 }
diff --git a/packages/tailwindcss-language-server/tests/code-actions/variant-order.json b/packages/tailwindcss-language-server/tests/code-actions/variant-order.json
index 6d44068f..d5b1491d 100644
--- a/packages/tailwindcss-language-server/tests/code-actions/variant-order.json
+++ b/packages/tailwindcss-language-server/tests/code-actions/variant-order.json
@@ -7,6 +7,7 @@
       "diagnostics": [
         {
           "code": "recommendedVariantOrder",
+          "source": "tailwindcss",
           "suggestions": ["focus:hover:uppercase"],
           "range": {
             "start": { "line": 0, "character": 12 },
diff --git a/packages/tailwindcss-language-server/tests/diagnostics/css-conflict/css.json b/packages/tailwindcss-language-server/tests/diagnostics/css-conflict/css.json
index da506bf1..0458b789 100644
--- a/packages/tailwindcss-language-server/tests/diagnostics/css-conflict/css.json
+++ b/packages/tailwindcss-language-server/tests/diagnostics/css-conflict/css.json
@@ -4,6 +4,7 @@
   "expected": [
     {
       "code": "cssConflict",
+      "source": "tailwindcss",
       "className": {
         "className": "uppercase",
         "classList": {
@@ -59,6 +60,7 @@
     },
     {
       "code": "cssConflict",
+      "source": "tailwindcss",
       "className": {
         "className": "lowercase",
         "classList": {
diff --git a/packages/tailwindcss-language-server/tests/diagnostics/css-conflict/jsx-concat-positive.json b/packages/tailwindcss-language-server/tests/diagnostics/css-conflict/jsx-concat-positive.json
index 39cbb515..fed900d7 100644
--- a/packages/tailwindcss-language-server/tests/diagnostics/css-conflict/jsx-concat-positive.json
+++ b/packages/tailwindcss-language-server/tests/diagnostics/css-conflict/jsx-concat-positive.json
@@ -4,6 +4,7 @@
   "expected": [
     {
       "code": "cssConflict",
+      "source": "tailwindcss",
       "className": {
         "className": "lowercase",
         "classList": {
@@ -57,6 +58,7 @@
     },
     {
       "code": "cssConflict",
+      "source": "tailwindcss",
       "className": {
         "className": "uppercase",
         "classList": {
diff --git a/packages/tailwindcss-language-server/tests/diagnostics/css-conflict/simple.json b/packages/tailwindcss-language-server/tests/diagnostics/css-conflict/simple.json
index c98280a1..08137dc7 100644
--- a/packages/tailwindcss-language-server/tests/diagnostics/css-conflict/simple.json
+++ b/packages/tailwindcss-language-server/tests/diagnostics/css-conflict/simple.json
@@ -3,6 +3,7 @@
   "expected": [
     {
       "code": "cssConflict",
+      "source": "tailwindcss",
       "className": {
         "className": "uppercase",
         "classList": {
@@ -56,6 +57,7 @@
     },
     {
       "code": "cssConflict",
+      "source": "tailwindcss",
       "className": {
         "className": "lowercase",
         "classList": {
diff --git a/packages/tailwindcss-language-server/tests/diagnostics/css-conflict/variants-positive.json b/packages/tailwindcss-language-server/tests/diagnostics/css-conflict/variants-positive.json
index 15fcb457..edcc7c4f 100644
--- a/packages/tailwindcss-language-server/tests/diagnostics/css-conflict/variants-positive.json
+++ b/packages/tailwindcss-language-server/tests/diagnostics/css-conflict/variants-positive.json
@@ -3,6 +3,7 @@
   "expected": [
     {
       "code": "cssConflict",
+      "source": "tailwindcss",
       "className": {
         "className": "sm:uppercase",
         "classList": {
@@ -56,6 +57,7 @@
     },
     {
       "code": "cssConflict",
+      "source": "tailwindcss",
       "className": {
         "className": "sm:lowercase",
         "classList": {
diff --git a/packages/tailwindcss-language-server/tests/diagnostics/css-conflict/vue-style-lang-sass.json b/packages/tailwindcss-language-server/tests/diagnostics/css-conflict/vue-style-lang-sass.json
index 7e9da86b..eaf85246 100644
--- a/packages/tailwindcss-language-server/tests/diagnostics/css-conflict/vue-style-lang-sass.json
+++ b/packages/tailwindcss-language-server/tests/diagnostics/css-conflict/vue-style-lang-sass.json
@@ -4,6 +4,7 @@
   "expected": [
     {
       "code": "cssConflict",
+      "source": "tailwindcss",
       "className": {
         "className": "uppercase",
         "classList": {
@@ -59,6 +60,7 @@
     },
     {
       "code": "cssConflict",
+      "source": "tailwindcss",
       "className": {
         "className": "lowercase",
         "classList": {
diff --git a/packages/tailwindcss-language-server/tests/diagnostics/diagnostics.test.js b/packages/tailwindcss-language-server/tests/diagnostics/diagnostics.test.js
index 42faee53..957185d0 100644
--- a/packages/tailwindcss-language-server/tests/diagnostics/diagnostics.test.js
+++ b/packages/tailwindcss-language-server/tests/diagnostics/diagnostics.test.js
@@ -95,6 +95,7 @@ withFixture('v4/basic', (c) => {
     expected: [
       {
         code: 'invalidConfigPath',
+        source: 'tailwindcss',
         range: { start: { line: 0, character: 21 }, end: { line: 0, character: 36 } },
         severity: 1,
         message: "'--color-red-901' does not exist in your theme. Did you mean '--color-red-900'?",
@@ -109,6 +110,7 @@ withFixture('v4/basic', (c) => {
     expected: [
       {
         code: 'invalidConfigPath',
+        source: 'tailwindcss',
         range: { start: { line: 0, character: 21 }, end: { line: 0, character: 37 } },
         severity: 1,
         message: "'--colors-red-901' does not exist in your theme. Did you mean '--color-red-900'?",
@@ -123,6 +125,7 @@ withFixture('v4/basic', (c) => {
     expected: [
       {
         code: 'invalidConfigPath',
+        source: 'tailwindcss',
         range: { start: { line: 0, character: 21 }, end: { line: 0, character: 42 } },
         severity: 1,
         message: "'--font-obliqueness-90' does not exist in your theme.",
@@ -143,6 +146,7 @@ withFixture('v4/basic', (c) => {
     expected: [
       {
         code: 'invalidConfigPath',
+        source: 'tailwindcss',
         range: { start: { line: 0, character: 21 }, end: { line: 0, character: 35 } },
         severity: 1,
         message: "'colors.red.901' does not exist in your theme config.",
@@ -194,6 +198,7 @@ withFixture('v4/with-prefix', (c) => {
     expected: [
       {
         code: 'invalidConfigPath',
+        source: 'tailwindcss',
         range: { start: { line: 0, character: 21 }, end: { line: 0, character: 36 } },
         severity: 1,
         message: "'--color-red-901' does not exist in your theme. Did you mean '--color-red-900'?",
@@ -208,6 +213,7 @@ withFixture('v4/with-prefix', (c) => {
     expected: [
       {
         code: 'invalidConfigPath',
+        source: 'tailwindcss',
         range: { start: { line: 0, character: 21 }, end: { line: 0, character: 37 } },
         severity: 1,
         message: "'--colors-red-901' does not exist in your theme. Did you mean '--color-red-900'?",
@@ -222,6 +228,7 @@ withFixture('v4/with-prefix', (c) => {
     expected: [
       {
         code: 'invalidConfigPath',
+        source: 'tailwindcss',
         range: { start: { line: 0, character: 21 }, end: { line: 0, character: 42 } },
         severity: 1,
         message: "'--font-obliqueness-90' does not exist in your theme.",
@@ -242,6 +249,7 @@ withFixture('v4/with-prefix', (c) => {
     expected: [
       {
         code: 'invalidConfigPath',
+        source: 'tailwindcss',
         range: { start: { line: 0, character: 21 }, end: { line: 0, character: 35 } },
         severity: 1,
         message: "'colors.red.901' does not exist in your theme config.",
@@ -280,6 +288,7 @@ withFixture('v4/basic', (c) => {
     expected: [
       {
         code: 'cssConflict',
+        source: 'tailwindcss',
         message: "'max-w-4xl' applies the same CSS properties as 'max-w-6xl'.",
         className: {
           className: 'max-w-4xl',
@@ -298,6 +307,7 @@ withFixture('v4/basic', (c) => {
       },
       {
         code: 'cssConflict',
+        source: 'tailwindcss',
         message: "'max-w-6xl' applies the same CSS properties as 'max-w-4xl'.",
         className: {
           className: 'max-w-6xl',
@@ -329,6 +339,7 @@ withFixture('v4/basic', (c) => {
     expected: [
       {
         code: 'invalidTailwindDirective',
+        source: 'tailwindcss',
         message:
           "'@tailwind base' is no longer available in v4. Use '@import \"tailwindcss/preflight\"' instead.",
         suggestions: [],
@@ -340,6 +351,7 @@ withFixture('v4/basic', (c) => {
       },
       {
         code: 'invalidTailwindDirective',
+        source: 'tailwindcss',
         message:
           "'@tailwind preflight' is no longer available in v4. Use '@import \"tailwindcss/preflight\"' instead.",
         suggestions: [],
@@ -351,6 +363,7 @@ withFixture('v4/basic', (c) => {
       },
       {
         code: 'invalidTailwindDirective',
+        source: 'tailwindcss',
         message:
           "'@tailwind components' is no longer available in v4. Use '@tailwind utilities' instead.",
         suggestions: ['utilities'],
@@ -362,6 +375,7 @@ withFixture('v4/basic', (c) => {
       },
       {
         code: 'invalidTailwindDirective',
+        source: 'tailwindcss',
         message:
           "'@tailwind screens' is no longer available in v4. Use '@tailwind utilities' instead.",
         suggestions: ['utilities'],
@@ -373,6 +387,7 @@ withFixture('v4/basic', (c) => {
       },
       {
         code: 'invalidTailwindDirective',
+        source: 'tailwindcss',
         message:
           "'@tailwind variants' is no longer available in v4. Use '@tailwind utilities' instead.",
         suggestions: ['utilities'],
@@ -406,6 +421,7 @@ defineTest({
     expect(diagnostics).toEqual([
       {
         code: 'usedBlocklistedClass',
+        source: 'tailwindcss',
         message: 'The class "flex" will not be generated as it has been blocklisted',
         range: {
           start: { line: 0, character: 12 },
@@ -415,6 +431,7 @@ defineTest({
       },
       {
         code: 'usedBlocklistedClass',
+        source: 'tailwindcss',
         message: 'The class "hover:flex" will not be generated as it has been blocklisted',
         range: {
           start: { line: 0, character: 27 },
@@ -463,6 +480,7 @@ defineTest({
     expect(diagnostics).toEqual([
       {
         code: 'suggestCanonicalClasses',
+        source: 'tailwindcss',
         message: 'The class `[@media_print]:flex` can be written as `print:flex`',
         range: {
           start: { line: 0, character: 12 },
@@ -473,6 +491,7 @@ defineTest({
       },
       {
         code: 'suggestCanonicalClasses',
+        source: 'tailwindcss',
         message: 'The class `[color:red]/50` can be written as `text-[red]/50`',
         range: {
           start: { line: 0, character: 32 },
@@ -483,6 +502,7 @@ defineTest({
       },
       {
         code: 'suggestCanonicalClasses',
+        source: 'tailwindcss',
         message: 'The class `mt-[16px]` can be written as `mt-4`',
         range: {
           start: { line: 0, character: 47 },
diff --git a/packages/tailwindcss-language-server/tests/diagnostics/invalid-screen/simple.json b/packages/tailwindcss-language-server/tests/diagnostics/invalid-screen/simple.json
index 61974b86..9fb1ded2 100644
--- a/packages/tailwindcss-language-server/tests/diagnostics/invalid-screen/simple.json
+++ b/packages/tailwindcss-language-server/tests/diagnostics/invalid-screen/simple.json
@@ -4,6 +4,7 @@
   "expected": [
     {
       "code": "invalidScreen",
+      "source": "tailwindcss",
       "range": { "start": { "line": 0, "character": 8 }, "end": { "line": 0, "character": 13 } },
       "severity": 1,
       "message": "The screen 'small' does not exist in your theme config. Did you mean 'sm'?",
diff --git a/packages/tailwindcss-language-server/tests/diagnostics/invalid-theme/simple.json b/packages/tailwindcss-language-server/tests/diagnostics/invalid-theme/simple.json
index 861a8b4e..3be41f4b 100644
--- a/packages/tailwindcss-language-server/tests/diagnostics/invalid-theme/simple.json
+++ b/packages/tailwindcss-language-server/tests/diagnostics/invalid-theme/simple.json
@@ -4,6 +4,7 @@
   "expected": [
     {
       "code": "invalidConfigPath",
+      "source": "tailwindcss",
       "range": { "start": { "line": 0, "character": 21 }, "end": { "line": 0, "character": 35 } },
       "severity": 1,
       "message": "'colors.red.901' does not exist in your theme config. Did you mean 'colors.red.900'?",
diff --git a/packages/tailwindcss-language-server/tests/diagnostics/source-diagnostics.test.js b/packages/tailwindcss-language-server/tests/diagnostics/source-diagnostics.test.js
index f6287b63..0024ed43 100644
--- a/packages/tailwindcss-language-server/tests/diagnostics/source-diagnostics.test.js
+++ b/packages/tailwindcss-language-server/tests/diagnostics/source-diagnostics.test.js
@@ -32,6 +32,7 @@ withFixture('v4/basic', (c) => {
     expected: [
       {
         code: 'invalidSourceDirective',
+        source: 'tailwindcss',
         message: 'The source directive requires a path to a directory.',
         range: {
           start: { line: 1, character: 35 },
@@ -40,6 +41,7 @@ withFixture('v4/basic', (c) => {
       },
       {
         code: 'invalidSourceDirective',
+        source: 'tailwindcss',
         message: 'The source directive requires a path to a directory.',
         range: {
           start: { line: 2, character: 35 },
@@ -48,6 +50,7 @@ withFixture('v4/basic', (c) => {
       },
       {
         code: 'invalidSourceDirective',
+        source: 'tailwindcss',
         message: 'The source directive requires a path to a directory.',
         range: {
           start: { line: 3, character: 35 },
@@ -56,6 +59,7 @@ withFixture('v4/basic', (c) => {
       },
       {
         code: 'invalidSourceDirective',
+        source: 'tailwindcss',
         message: 'The source directive requires a path to a directory.',
         range: {
           start: { line: 4, character: 33 },
@@ -64,6 +68,7 @@ withFixture('v4/basic', (c) => {
       },
       {
         code: 'invalidSourceDirective',
+        source: 'tailwindcss',
         message: 'The source directive requires a path to a directory.',
         range: {
           start: { line: 5, character: 33 },
@@ -72,6 +77,7 @@ withFixture('v4/basic', (c) => {
       },
       {
         code: 'invalidSourceDirective',
+        source: 'tailwindcss',
         message: 'The source directive requires a path to a directory.',
         range: {
           start: { line: 6, character: 33 },
@@ -90,6 +96,7 @@ withFixture('v4/basic', (c) => {
     expected: [
       {
         code: 'invalidSourceDirective',
+        source: 'tailwindcss',
         message: '`source(no)` is invalid. Did you mean `source(none)`?',
         range: {
           start: { line: 1, character: 35 },
@@ -98,6 +105,7 @@ withFixture('v4/basic', (c) => {
       },
       {
         code: 'invalidSourceDirective',
+        source: 'tailwindcss',
         message: '`source(no)` is invalid. Did you mean `source(none)`?',
         range: {
           start: { line: 2, character: 33 },
@@ -127,6 +135,7 @@ withFixture('v4/basic', (c) => {
     expected: [
       {
         code: 'invalidSourceDirective',
+        source: 'tailwindcss',
         message:
           'POSIX-style paths are required with `source(…)` but `C:\\absolute\\path` is a Windows-style path.',
         range: {
@@ -136,6 +145,7 @@ withFixture('v4/basic', (c) => {
       },
       {
         code: 'invalidSourceDirective',
+        source: 'tailwindcss',
         message:
           'POSIX-style paths are required with `source(…)` but `C:relative.txt` is a Windows-style path.',
         range: {
diff --git a/packages/tailwindcss-language-service/src/diagnostics/canonical-classes.ts b/packages/tailwindcss-language-service/src/diagnostics/canonical-classes.ts
index 3f30f337..d7e3dfe9 100644
--- a/packages/tailwindcss-language-service/src/diagnostics/canonical-classes.ts
+++ b/packages/tailwindcss-language-service/src/diagnostics/canonical-classes.ts
@@ -46,6 +46,7 @@ export async function getSuggestCanonicalClassesDiagnostics(
 
       diagnostics.push({
         code: DiagnosticKind.SuggestCanonicalClasses,
+        source: 'tailwindcss',
         range: className.range,
         severity:
           severity === 'error'
diff --git a/packages/tailwindcss-language-service/src/diagnostics/getCssConflictDiagnostics.ts b/packages/tailwindcss-language-service/src/diagnostics/getCssConflictDiagnostics.ts
index dcf61089..09317bf6 100644
--- a/packages/tailwindcss-language-service/src/diagnostics/getCssConflictDiagnostics.ts
+++ b/packages/tailwindcss-language-service/src/diagnostics/getCssConflictDiagnostics.ts
@@ -60,6 +60,7 @@ export async function getCssConflictDiagnostics(
       for (let [className, conflictingClassNames] of findConflicts(classNames, groups)) {
         diagnostics.push({
           code: DiagnosticKind.CssConflict,
+          source: 'tailwindcss',
           className,
           otherClassNames: conflictingClassNames,
           range: className.range,
@@ -144,6 +145,7 @@ export async function getCssConflictDiagnostics(
 
         diagnostics.push({
           code: DiagnosticKind.CssConflict,
+          source: 'tailwindcss',
           className,
           otherClassNames: conflictingClassNames,
           range: className.range,
@@ -198,6 +200,7 @@ export async function getCssConflictDiagnostics(
 
       diagnostics.push({
         code: DiagnosticKind.CssConflict,
+        source: 'tailwindcss',
         className,
         otherClassNames: conflictingClassNames,
         range: className.range,
diff --git a/packages/tailwindcss-language-service/src/diagnostics/getInvalidApplyDiagnostics.ts b/packages/tailwindcss-language-service/src/diagnostics/getInvalidApplyDiagnostics.ts
index bb1cca60..ca9a2d82 100644
--- a/packages/tailwindcss-language-service/src/diagnostics/getInvalidApplyDiagnostics.ts
+++ b/packages/tailwindcss-language-service/src/diagnostics/getInvalidApplyDiagnostics.ts
@@ -23,6 +23,7 @@ export async function getInvalidApplyDiagnostics(
 
     return {
       code: DiagnosticKind.InvalidApply,
+      source: 'tailwindcss',
       severity:
         severity === 'error'
           ? 1 /* DiagnosticSeverity.Error */
diff --git a/packages/tailwindcss-language-service/src/diagnostics/getInvalidConfigPathDiagnostics.ts b/packages/tailwindcss-language-service/src/diagnostics/getInvalidConfigPathDiagnostics.ts
index 76864281..1d36d4b6 100644
--- a/packages/tailwindcss-language-service/src/diagnostics/getInvalidConfigPathDiagnostics.ts
+++ b/packages/tailwindcss-language-service/src/diagnostics/getInvalidConfigPathDiagnostics.ts
@@ -199,6 +199,7 @@ export function getInvalidConfigPathDiagnostics(
 
     diagnostics.push({
       code: DiagnosticKind.InvalidConfigPath,
+      source: 'tailwindcss',
       range: helperFn.ranges.path,
       severity:
         severity === 'error'
diff --git a/packages/tailwindcss-language-service/src/diagnostics/getInvalidScreenDiagnostics.ts b/packages/tailwindcss-language-service/src/diagnostics/getInvalidScreenDiagnostics.ts
index f03c672c..7eef058b 100644
--- a/packages/tailwindcss-language-service/src/diagnostics/getInvalidScreenDiagnostics.ts
+++ b/packages/tailwindcss-language-service/src/diagnostics/getInvalidScreenDiagnostics.ts
@@ -48,6 +48,7 @@ export function getInvalidScreenDiagnostics(
 
       diagnostics.push({
         code: DiagnosticKind.InvalidScreen,
+        source: 'tailwindcss',
         range: absoluteRange(
           {
             start: indexToPosition(
diff --git a/packages/tailwindcss-language-service/src/diagnostics/getInvalidSourceDiagnostics.ts b/packages/tailwindcss-language-service/src/diagnostics/getInvalidSourceDiagnostics.ts
index 24fdcd9c..b7a948ca 100644
--- a/packages/tailwindcss-language-service/src/diagnostics/getInvalidSourceDiagnostics.ts
+++ b/packages/tailwindcss-language-service/src/diagnostics/getInvalidSourceDiagnostics.ts
@@ -31,6 +31,7 @@ export function getInvalidSourceDiagnostics(
   function add(diag: Omit<InvalidSourceDirectiveDiagnostic, 'code' | 'severity'>) {
     diagnostics.push({
       code: DiagnosticKind.InvalidSourceDirective,
+      source: 'tailwindcss',
       severity:
         severity === 'error'
           ? 1 /* DiagnosticSeverity.Error */
diff --git a/packages/tailwindcss-language-service/src/diagnostics/getInvalidTailwindDirectiveDiagnostics.ts b/packages/tailwindcss-language-service/src/diagnostics/getInvalidTailwindDirectiveDiagnostics.ts
index 480bb8cd..7d98ff5d 100644
--- a/packages/tailwindcss-language-service/src/diagnostics/getInvalidTailwindDirectiveDiagnostics.ts
+++ b/packages/tailwindcss-language-service/src/diagnostics/getInvalidTailwindDirectiveDiagnostics.ts
@@ -51,6 +51,7 @@ export function getInvalidTailwindDirectiveDiagnostics(
 
       diagnostics.push({
         code: DiagnosticKind.InvalidTailwindDirective,
+        source: 'tailwindcss',
         range: absoluteRange(
           {
             start: indexToPosition(text, match.index + match[0].length - layerName.length),
diff --git a/packages/tailwindcss-language-service/src/diagnostics/getInvalidVariantDiagnostics.ts b/packages/tailwindcss-language-service/src/diagnostics/getInvalidVariantDiagnostics.ts
index 1401e2ee..923f1dd9 100644
--- a/packages/tailwindcss-language-service/src/diagnostics/getInvalidVariantDiagnostics.ts
+++ b/packages/tailwindcss-language-service/src/diagnostics/getInvalidVariantDiagnostics.ts
@@ -73,6 +73,7 @@ export function getInvalidVariantDiagnostics(
 
         diagnostics.push({
           code: DiagnosticKind.InvalidVariant,
+          source: 'tailwindcss',
           range: absoluteRange(
             {
               start: indexToPosition(text, variantStartIndex),
diff --git a/packages/tailwindcss-language-service/src/diagnostics/getRecommendedVariantOrderDiagnostics.ts b/packages/tailwindcss-language-service/src/diagnostics/getRecommendedVariantOrderDiagnostics.ts
index 11ce2fcd..959bb87f 100644
--- a/packages/tailwindcss-language-service/src/diagnostics/getRecommendedVariantOrderDiagnostics.ts
+++ b/packages/tailwindcss-language-service/src/diagnostics/getRecommendedVariantOrderDiagnostics.ts
@@ -38,6 +38,7 @@ export async function getRecommendedVariantOrderDiagnostics(
       if (!equalExact(variants, sortedVariants)) {
         diagnostics.push({
           code: DiagnosticKind.RecommendedVariantOrder,
+          source: 'tailwindcss',
           suggestions: [
             [...sortedVariants, className.className.substr(offset)].join(state.separator),
           ],
diff --git a/packages/tailwindcss-language-service/src/diagnostics/getUsedBlocklistedClassDiagnostics.ts b/packages/tailwindcss-language-service/src/diagnostics/getUsedBlocklistedClassDiagnostics.ts
index 07f1084c..a0743eae 100644
--- a/packages/tailwindcss-language-service/src/diagnostics/getUsedBlocklistedClassDiagnostics.ts
+++ b/packages/tailwindcss-language-service/src/diagnostics/getUsedBlocklistedClassDiagnostics.ts
@@ -27,6 +27,7 @@ export async function getUsedBlocklistedClassDiagnostics(
 
       diagnostics.push({
         code: DiagnosticKind.UsedBlocklistedClass,
+        source: 'tailwindcss',
         range: className.range,
         severity:
           severity === 'error'
diff --git a/packages/vscode-tailwindcss/CHANGELOG.md b/packages/vscode-tailwindcss/CHANGELOG.md
index ae2344e5..d8c536d0 100644
--- a/packages/vscode-tailwindcss/CHANGELOG.md
+++ b/packages/vscode-tailwindcss/CHANGELOG.md
@@ -2,7 +2,7 @@
 
 ## Prerelease
 
-- Nothing yet!
+- Add a source to all emitted diagnostics ([#1491](https://github.com/tailwindlabs/tailwindcss-intellisense/pull/1491))
 
 ## 0.14.29