diff --git a/apps/oxlint/test/fixtures/basic_custom_plugin/.oxlintrc.json b/apps/oxlint/test/fixtures/basic_custom_plugin/.oxlintrc.json
index 609fce374189b..9d64fb3636b2d 100644
--- a/apps/oxlint/test/fixtures/basic_custom_plugin/.oxlintrc.json
+++ b/apps/oxlint/test/fixtures/basic_custom_plugin/.oxlintrc.json
@@ -1,5 +1,5 @@
 {
-  "jsPlugins": ["./plugin.js"],
+  "jsPlugins": ["./plugin.ts"],
   "rules": {
     "basic-custom-plugin/no-debugger": "error"
   }
diff --git a/apps/oxlint/test/fixtures/basic_custom_plugin/plugin.js b/apps/oxlint/test/fixtures/basic_custom_plugin/plugin.ts
similarity index 77%
rename from apps/oxlint/test/fixtures/basic_custom_plugin/plugin.js
rename to apps/oxlint/test/fixtures/basic_custom_plugin/plugin.ts
index d401a98de06ee..d8f0b772b32f1 100644
--- a/apps/oxlint/test/fixtures/basic_custom_plugin/plugin.js
+++ b/apps/oxlint/test/fixtures/basic_custom_plugin/plugin.ts
@@ -1,4 +1,6 @@
-export default {
+import type { Plugin } from '../../../dist/index.js';
+
+const plugin: Plugin = {
   meta: {
     name: 'basic-custom-plugin',
   },
@@ -17,3 +19,5 @@ export default {
     },
   },
 };
+
+export default plugin;
diff --git a/apps/oxlint/test/fixtures/basic_custom_plugin_many_files/.oxlintrc.json b/apps/oxlint/test/fixtures/basic_custom_plugin_many_files/.oxlintrc.json
index 609fce374189b..9d64fb3636b2d 100644
--- a/apps/oxlint/test/fixtures/basic_custom_plugin_many_files/.oxlintrc.json
+++ b/apps/oxlint/test/fixtures/basic_custom_plugin_many_files/.oxlintrc.json
@@ -1,5 +1,5 @@
 {
-  "jsPlugins": ["./plugin.js"],
+  "jsPlugins": ["./plugin.ts"],
   "rules": {
     "basic-custom-plugin/no-debugger": "error"
   }
diff --git a/apps/oxlint/test/fixtures/basic_custom_plugin_many_files/plugin.js b/apps/oxlint/test/fixtures/basic_custom_plugin_many_files/plugin.ts
similarity index 77%
rename from apps/oxlint/test/fixtures/basic_custom_plugin_many_files/plugin.js
rename to apps/oxlint/test/fixtures/basic_custom_plugin_many_files/plugin.ts
index d401a98de06ee..d8f0b772b32f1 100644
--- a/apps/oxlint/test/fixtures/basic_custom_plugin_many_files/plugin.js
+++ b/apps/oxlint/test/fixtures/basic_custom_plugin_many_files/plugin.ts
@@ -1,4 +1,6 @@
-export default {
+import type { Plugin } from '../../../dist/index.js';
+
+const plugin: Plugin = {
   meta: {
     name: 'basic-custom-plugin',
   },
@@ -17,3 +19,5 @@ export default {
     },
   },
 };
+
+export default plugin;
diff --git a/apps/oxlint/test/fixtures/basic_custom_plugin_multiple_rules/.oxlintrc.json b/apps/oxlint/test/fixtures/basic_custom_plugin_multiple_rules/.oxlintrc.json
index 2abdbca974ff5..50897d6f21757 100644
--- a/apps/oxlint/test/fixtures/basic_custom_plugin_multiple_rules/.oxlintrc.json
+++ b/apps/oxlint/test/fixtures/basic_custom_plugin_multiple_rules/.oxlintrc.json
@@ -1,5 +1,5 @@
 {
-  "jsPlugins": ["./plugin.js"],
+  "jsPlugins": ["./plugin.ts"],
   "rules": {
     "basic-custom-plugin/no-debugger": "error",
     "basic-custom-plugin/no-debugger-2": "error",
diff --git a/apps/oxlint/test/fixtures/basic_custom_plugin_multiple_rules/plugin.js b/apps/oxlint/test/fixtures/basic_custom_plugin_multiple_rules/plugin.ts
similarity index 90%
rename from apps/oxlint/test/fixtures/basic_custom_plugin_multiple_rules/plugin.js
rename to apps/oxlint/test/fixtures/basic_custom_plugin_multiple_rules/plugin.ts
index f01f07780343a..b09ba9139af5a 100644
--- a/apps/oxlint/test/fixtures/basic_custom_plugin_multiple_rules/plugin.js
+++ b/apps/oxlint/test/fixtures/basic_custom_plugin_multiple_rules/plugin.ts
@@ -1,4 +1,6 @@
-export default {
+import type { Plugin } from '../../../dist/index.js';
+
+const plugin: Plugin = {
   meta: {
     name: 'basic-custom-plugin',
   },
@@ -40,3 +42,5 @@ export default {
     },
   },
 };
+
+export default plugin;
diff --git a/apps/oxlint/test/fixtures/basic_custom_plugin_warn_severity/.oxlintrc.json b/apps/oxlint/test/fixtures/basic_custom_plugin_warn_severity/.oxlintrc.json
index b42196762d223..7a92c43dcf652 100644
--- a/apps/oxlint/test/fixtures/basic_custom_plugin_warn_severity/.oxlintrc.json
+++ b/apps/oxlint/test/fixtures/basic_custom_plugin_warn_severity/.oxlintrc.json
@@ -1,5 +1,5 @@
 {
-  "jsPlugins": ["./plugin.js"],
+  "jsPlugins": ["./plugin.ts"],
   "rules": {
     "basic-custom-plugin/no-debugger": "warn"
   }
diff --git a/apps/oxlint/test/fixtures/custom_plugin_via_overrides/plugin.js b/apps/oxlint/test/fixtures/basic_custom_plugin_warn_severity/plugin.ts
similarity index 77%
rename from apps/oxlint/test/fixtures/custom_plugin_via_overrides/plugin.js
rename to apps/oxlint/test/fixtures/basic_custom_plugin_warn_severity/plugin.ts
index d401a98de06ee..d8f0b772b32f1 100644
--- a/apps/oxlint/test/fixtures/custom_plugin_via_overrides/plugin.js
+++ b/apps/oxlint/test/fixtures/basic_custom_plugin_warn_severity/plugin.ts
@@ -1,4 +1,6 @@
-export default {
+import type { Plugin } from '../../../dist/index.js';
+
+const plugin: Plugin = {
   meta: {
     name: 'basic-custom-plugin',
   },
@@ -17,3 +19,5 @@ export default {
     },
   },
 };
+
+export default plugin;
diff --git a/apps/oxlint/test/fixtures/context_properties/.oxlintrc.json b/apps/oxlint/test/fixtures/context_properties/.oxlintrc.json
index 0c767785ffa52..0f586788f5810 100644
--- a/apps/oxlint/test/fixtures/context_properties/.oxlintrc.json
+++ b/apps/oxlint/test/fixtures/context_properties/.oxlintrc.json
@@ -1,5 +1,5 @@
 {
-  "jsPlugins": ["./plugin.js"],
+  "jsPlugins": ["./plugin.ts"],
   "categories": { "correctness": "off" },
   "rules": {
     "context-plugin/log-context": "error"
diff --git a/apps/oxlint/test/fixtures/context_properties/plugin.js b/apps/oxlint/test/fixtures/context_properties/plugin.ts
similarity index 77%
rename from apps/oxlint/test/fixtures/context_properties/plugin.js
rename to apps/oxlint/test/fixtures/context_properties/plugin.ts
index 2a0b74bbc3bd8..022584b4d2ab2 100644
--- a/apps/oxlint/test/fixtures/context_properties/plugin.js
+++ b/apps/oxlint/test/fixtures/context_properties/plugin.ts
@@ -1,14 +1,16 @@
 import { sep } from 'node:path';
 
+import type { Plugin, Rule } from '../../../dist/index.js';
+
 const SPAN = { start: 0, end: 0 };
 
 const DIR_PATH_LEN = import.meta.dirname.length + 1;
 
 const relativePath = sep === '/'
-  ? path => path.slice(DIR_PATH_LEN)
-  : path => path.slice(DIR_PATH_LEN).replace(/\\/g, '/');
+  ? (path: string) => path.slice(DIR_PATH_LEN)
+  : (path: string) => path.slice(DIR_PATH_LEN).replace(/\\/g, '/');
 
-const rule = {
+const rule: Rule = {
   create(context) {
     context.report({
       message: `id: ${context.id}`,
@@ -35,7 +37,7 @@ const rule = {
   },
 };
 
-export default {
+const plugin: Plugin = {
   meta: {
     name: 'context-plugin',
   },
@@ -43,3 +45,5 @@ export default {
     'log-context': rule,
   },
 };
+
+export default plugin;
diff --git a/apps/oxlint/test/fixtures/createOnce/.oxlintrc.json b/apps/oxlint/test/fixtures/createOnce/.oxlintrc.json
index 5a73b5a80228e..3815e58a08cfc 100644
--- a/apps/oxlint/test/fixtures/createOnce/.oxlintrc.json
+++ b/apps/oxlint/test/fixtures/createOnce/.oxlintrc.json
@@ -1,5 +1,5 @@
 {
-  "jsPlugins": ["./plugin.js"],
+  "jsPlugins": ["./plugin.ts"],
   "categories": { "correctness": "off" },
   "rules": {
     "create-once-plugin/always-run": "error",
diff --git a/apps/oxlint/test/fixtures/createOnce/plugin.js b/apps/oxlint/test/fixtures/createOnce/plugin.ts
similarity index 88%
rename from apps/oxlint/test/fixtures/createOnce/plugin.js
rename to apps/oxlint/test/fixtures/createOnce/plugin.ts
index 7eb7dbcfeac4e..376209afcc3a5 100644
--- a/apps/oxlint/test/fixtures/createOnce/plugin.js
+++ b/apps/oxlint/test/fixtures/createOnce/plugin.ts
@@ -1,18 +1,23 @@
 import { sep } from 'node:path';
 
+import type { Plugin, Rule } from '../../../dist/index.js';
+
 const SPAN = { start: 0, end: 0 };
 
 const DIR_PATH_LEN = import.meta.dirname.length + 1;
 
 const relativePath = sep === '/'
-  ? path => path.slice(DIR_PATH_LEN)
-  : path => path.slice(DIR_PATH_LEN).replace(/\\/g, '/');
+  ? (path: string) => path.slice(DIR_PATH_LEN)
+  : (path: string) => path.slice(DIR_PATH_LEN).replace(/\\/g, '/');
 
 let createOnceCallCount = 0;
-const alwaysRunRule = {
+
+const alwaysRunRule: Rule = {
   createOnce(context) {
     createOnceCallCount++;
 
+    // `this` should be the rule object
+    // oxlint-disable-next-line typescript-eslint/no-this-alias
     const topLevelThis = this;
 
     // Check that these APIs throw here
@@ -49,7 +54,7 @@ const alwaysRunRule = {
   },
 };
 
-const skipRunRule = {
+const skipRunRule: Rule = {
   createOnce(context) {
     return {
       before() {
@@ -68,7 +73,7 @@ const skipRunRule = {
   },
 };
 
-const beforeOnlyRule = {
+const beforeOnlyRule: Rule = {
   createOnce(context) {
     return {
       before() {
@@ -85,7 +90,7 @@ const beforeOnlyRule = {
   },
 };
 
-const afterOnlyRule = {
+const afterOnlyRule: Rule = {
   createOnce(context) {
     return {
       Identifier(node) {
@@ -102,7 +107,7 @@ const afterOnlyRule = {
   },
 };
 
-const noHooksRule = {
+const noHooksRule: Rule = {
   createOnce(context) {
     return {
       Identifier(node) {
@@ -115,7 +120,7 @@ const noHooksRule = {
   },
 };
 
-export default {
+const plugin: Plugin = {
   meta: {
     name: 'create-once-plugin',
   },
@@ -128,7 +133,9 @@ export default {
   },
 };
 
-function tryCatch(fn) {
+export default plugin;
+
+function tryCatch(fn: () => unknown) {
   try {
     fn();
   } catch (err) {
diff --git a/apps/oxlint/test/fixtures/custom_plugin_disable_directives/.oxlintrc.json b/apps/oxlint/test/fixtures/custom_plugin_disable_directives/.oxlintrc.json
index bd342e8fa2f25..174ab0f1c62a2 100644
--- a/apps/oxlint/test/fixtures/custom_plugin_disable_directives/.oxlintrc.json
+++ b/apps/oxlint/test/fixtures/custom_plugin_disable_directives/.oxlintrc.json
@@ -1,5 +1,5 @@
 {
-  "jsPlugins": ["./plugin.js"],
+  "jsPlugins": ["./plugin.ts"],
   "categories": { "correctness": "off" },
   "rules": {
     "test-plugin/no-var": "error",
diff --git a/apps/oxlint/test/fixtures/custom_plugin_disable_directives/plugin.js b/apps/oxlint/test/fixtures/custom_plugin_disable_directives/plugin.ts
similarity index 78%
rename from apps/oxlint/test/fixtures/custom_plugin_disable_directives/plugin.js
rename to apps/oxlint/test/fixtures/custom_plugin_disable_directives/plugin.ts
index e562c874849d0..62ff992daa53d 100644
--- a/apps/oxlint/test/fixtures/custom_plugin_disable_directives/plugin.js
+++ b/apps/oxlint/test/fixtures/custom_plugin_disable_directives/plugin.ts
@@ -1,4 +1,6 @@
-export default {
+import type { Plugin } from '../../../dist/index.js';
+
+const plugin: Plugin = {
   meta: {
     name: 'test-plugin',
   },
@@ -19,3 +21,5 @@ export default {
     },
   },
 };
+
+export default plugin;
diff --git a/apps/oxlint/test/fixtures/custom_plugin_import_error/.oxlintrc.json b/apps/oxlint/test/fixtures/custom_plugin_import_error/.oxlintrc.json
index 81ab9e9a22252..c36bad1c7cf08 100644
--- a/apps/oxlint/test/fixtures/custom_plugin_import_error/.oxlintrc.json
+++ b/apps/oxlint/test/fixtures/custom_plugin_import_error/.oxlintrc.json
@@ -1,5 +1,5 @@
 {
-  "jsPlugins": ["./plugin.js"],
+  "jsPlugins": ["./plugin.ts"],
   "categories": { "correctness": "off" },
   "rules": {
     "basic-custom-plugin/unknown-rule": "error"
diff --git a/apps/oxlint/test/fixtures/custom_plugin_import_error/output.snap.md b/apps/oxlint/test/fixtures/custom_plugin_import_error/output.snap.md
index 9297d670ca48e..bd8d5093281c2 100644
--- a/apps/oxlint/test/fixtures/custom_plugin_import_error/output.snap.md
+++ b/apps/oxlint/test/fixtures/custom_plugin_import_error/output.snap.md
@@ -5,9 +5,9 @@
 ```
 Failed to parse configuration file.
 
-  x Failed to load JS plugin: ./plugin.js
+  x Failed to load JS plugin: ./plugin.ts
   |   Error: whoops!
-  |     at <root>/apps/oxlint/test/fixtures/custom_plugin_import_error/plugin.js:1:7
+  |     at <root>/apps/oxlint/test/fixtures/custom_plugin_import_error/plugin.ts:1:7
 ```
 
 # stderr
diff --git a/apps/oxlint/test/fixtures/custom_plugin_import_error/plugin.js b/apps/oxlint/test/fixtures/custom_plugin_import_error/plugin.ts
similarity index 100%
rename from apps/oxlint/test/fixtures/custom_plugin_import_error/plugin.js
rename to apps/oxlint/test/fixtures/custom_plugin_import_error/plugin.ts
diff --git a/apps/oxlint/test/fixtures/custom_plugin_lint_after_hook_error/.oxlintrc.json b/apps/oxlint/test/fixtures/custom_plugin_lint_after_hook_error/.oxlintrc.json
index eac0cd7034245..76b546efca906 100644
--- a/apps/oxlint/test/fixtures/custom_plugin_lint_after_hook_error/.oxlintrc.json
+++ b/apps/oxlint/test/fixtures/custom_plugin_lint_after_hook_error/.oxlintrc.json
@@ -1,5 +1,5 @@
 {
-  "jsPlugins": ["./plugin.js"],
+  "jsPlugins": ["./plugin.ts"],
   "categories": { "correctness": "off" },
   "rules": {
     "error-plugin/error": "error"
diff --git a/apps/oxlint/test/fixtures/custom_plugin_lint_after_hook_error/output.snap.md b/apps/oxlint/test/fixtures/custom_plugin_lint_after_hook_error/output.snap.md
index 6bee5e2dd5256..53623b649dd94 100644
--- a/apps/oxlint/test/fixtures/custom_plugin_lint_after_hook_error/output.snap.md
+++ b/apps/oxlint/test/fixtures/custom_plugin_lint_after_hook_error/output.snap.md
@@ -6,7 +6,7 @@
   x Error running JS plugin.
   | File path: <root>/apps/oxlint/test/fixtures/custom_plugin_lint_after_hook_error/files/index.js
   | Error: Whoops!
-  |     at after (<root>/apps/oxlint/test/fixtures/custom_plugin_lint_after_hook_error/plugin.js:10:19)
+  |     at after (<root>/apps/oxlint/test/fixtures/custom_plugin_lint_after_hook_error/plugin.ts:12:19)
 
 Found 0 warnings and 1 error.
 Finished in Xms on 1 file using X threads.
diff --git a/apps/oxlint/test/fixtures/custom_plugin_lint_after_hook_error/plugin.js b/apps/oxlint/test/fixtures/custom_plugin_lint_after_hook_error/plugin.ts
similarity index 67%
rename from apps/oxlint/test/fixtures/custom_plugin_lint_after_hook_error/plugin.js
rename to apps/oxlint/test/fixtures/custom_plugin_lint_after_hook_error/plugin.ts
index 6b19fab66bd6b..29b965907147a 100644
--- a/apps/oxlint/test/fixtures/custom_plugin_lint_after_hook_error/plugin.js
+++ b/apps/oxlint/test/fixtures/custom_plugin_lint_after_hook_error/plugin.ts
@@ -1,4 +1,6 @@
-export default {
+import type { Plugin } from '../../../dist/index.js';
+
+const plugin: Plugin = {
   meta: {
     name: 'error-plugin',
   },
@@ -14,3 +16,5 @@ export default {
     },
   },
 };
+
+export default plugin;
diff --git a/apps/oxlint/test/fixtures/custom_plugin_lint_before_hook_error/.oxlintrc.json b/apps/oxlint/test/fixtures/custom_plugin_lint_before_hook_error/.oxlintrc.json
index eac0cd7034245..76b546efca906 100644
--- a/apps/oxlint/test/fixtures/custom_plugin_lint_before_hook_error/.oxlintrc.json
+++ b/apps/oxlint/test/fixtures/custom_plugin_lint_before_hook_error/.oxlintrc.json
@@ -1,5 +1,5 @@
 {
-  "jsPlugins": ["./plugin.js"],
+  "jsPlugins": ["./plugin.ts"],
   "categories": { "correctness": "off" },
   "rules": {
     "error-plugin/error": "error"
diff --git a/apps/oxlint/test/fixtures/custom_plugin_lint_before_hook_error/output.snap.md b/apps/oxlint/test/fixtures/custom_plugin_lint_before_hook_error/output.snap.md
index 2beefd11f40a7..990a389d81b53 100644
--- a/apps/oxlint/test/fixtures/custom_plugin_lint_before_hook_error/output.snap.md
+++ b/apps/oxlint/test/fixtures/custom_plugin_lint_before_hook_error/output.snap.md
@@ -6,7 +6,7 @@
   x Error running JS plugin.
   | File path: <root>/apps/oxlint/test/fixtures/custom_plugin_lint_before_hook_error/files/index.js
   | Error: Whoops!
-  |     at before (<root>/apps/oxlint/test/fixtures/custom_plugin_lint_before_hook_error/plugin.js:10:19)
+  |     at before (<root>/apps/oxlint/test/fixtures/custom_plugin_lint_before_hook_error/plugin.ts:12:19)
 
 Found 0 warnings and 1 error.
 Finished in Xms on 1 file using X threads.
diff --git a/apps/oxlint/test/fixtures/custom_plugin_lint_before_hook_error/plugin.js b/apps/oxlint/test/fixtures/custom_plugin_lint_before_hook_error/plugin.ts
similarity index 67%
rename from apps/oxlint/test/fixtures/custom_plugin_lint_before_hook_error/plugin.js
rename to apps/oxlint/test/fixtures/custom_plugin_lint_before_hook_error/plugin.ts
index 643fca6ea8189..dc24ecff54784 100644
--- a/apps/oxlint/test/fixtures/custom_plugin_lint_before_hook_error/plugin.js
+++ b/apps/oxlint/test/fixtures/custom_plugin_lint_before_hook_error/plugin.ts
@@ -1,4 +1,6 @@
-export default {
+import type { Plugin } from '../../../dist/index.js';
+
+const plugin: Plugin = {
   meta: {
     name: 'error-plugin',
   },
@@ -14,3 +16,5 @@ export default {
     },
   },
 };
+
+export default plugin;
diff --git a/apps/oxlint/test/fixtures/custom_plugin_lint_createOnce_error/.oxlintrc.json b/apps/oxlint/test/fixtures/custom_plugin_lint_createOnce_error/.oxlintrc.json
index eac0cd7034245..76b546efca906 100644
--- a/apps/oxlint/test/fixtures/custom_plugin_lint_createOnce_error/.oxlintrc.json
+++ b/apps/oxlint/test/fixtures/custom_plugin_lint_createOnce_error/.oxlintrc.json
@@ -1,5 +1,5 @@
 {
-  "jsPlugins": ["./plugin.js"],
+  "jsPlugins": ["./plugin.ts"],
   "categories": { "correctness": "off" },
   "rules": {
     "error-plugin/error": "error"
diff --git a/apps/oxlint/test/fixtures/custom_plugin_lint_createOnce_error/output.snap.md b/apps/oxlint/test/fixtures/custom_plugin_lint_createOnce_error/output.snap.md
index 8ebc8356c12a3..f67fbe33db122 100644
--- a/apps/oxlint/test/fixtures/custom_plugin_lint_createOnce_error/output.snap.md
+++ b/apps/oxlint/test/fixtures/custom_plugin_lint_createOnce_error/output.snap.md
@@ -5,9 +5,9 @@
 ```
 Failed to parse configuration file.
 
-  x Failed to load JS plugin: ./plugin.js
+  x Failed to load JS plugin: ./plugin.ts
   |   Error: Whoops!
-  |     at Object.createOnce (<root>/apps/oxlint/test/fixtures/custom_plugin_lint_createOnce_error/plugin.js:8:15)
+  |     at Object.createOnce (<root>/apps/oxlint/test/fixtures/custom_plugin_lint_createOnce_error/plugin.ts:10:15)
 ```
 
 # stderr
diff --git a/apps/oxlint/test/fixtures/custom_plugin_lint_createOnce_error/plugin.js b/apps/oxlint/test/fixtures/custom_plugin_lint_createOnce_error/plugin.ts
similarity index 59%
rename from apps/oxlint/test/fixtures/custom_plugin_lint_createOnce_error/plugin.js
rename to apps/oxlint/test/fixtures/custom_plugin_lint_createOnce_error/plugin.ts
index d804fe74862cc..eea86ab9fa8ce 100644
--- a/apps/oxlint/test/fixtures/custom_plugin_lint_createOnce_error/plugin.js
+++ b/apps/oxlint/test/fixtures/custom_plugin_lint_createOnce_error/plugin.ts
@@ -1,4 +1,6 @@
-export default {
+import type { Plugin } from '../../../dist/index.js';
+
+const plugin: Plugin = {
   meta: {
     name: 'error-plugin',
   },
@@ -10,3 +12,5 @@ export default {
     },
   },
 };
+
+export default plugin;
diff --git a/apps/oxlint/test/fixtures/custom_plugin_lint_create_error/.oxlintrc.json b/apps/oxlint/test/fixtures/custom_plugin_lint_create_error/.oxlintrc.json
index eac0cd7034245..76b546efca906 100644
--- a/apps/oxlint/test/fixtures/custom_plugin_lint_create_error/.oxlintrc.json
+++ b/apps/oxlint/test/fixtures/custom_plugin_lint_create_error/.oxlintrc.json
@@ -1,5 +1,5 @@
 {
-  "jsPlugins": ["./plugin.js"],
+  "jsPlugins": ["./plugin.ts"],
   "categories": { "correctness": "off" },
   "rules": {
     "error-plugin/error": "error"
diff --git a/apps/oxlint/test/fixtures/custom_plugin_lint_create_error/output.snap.md b/apps/oxlint/test/fixtures/custom_plugin_lint_create_error/output.snap.md
index 6518746157b5c..af278bd6d5ccc 100644
--- a/apps/oxlint/test/fixtures/custom_plugin_lint_create_error/output.snap.md
+++ b/apps/oxlint/test/fixtures/custom_plugin_lint_create_error/output.snap.md
@@ -6,7 +6,7 @@
   x Error running JS plugin.
   | File path: <root>/apps/oxlint/test/fixtures/custom_plugin_lint_create_error/files/index.js
   | Error: Whoops!
-  |     at Object.create (<root>/apps/oxlint/test/fixtures/custom_plugin_lint_create_error/plugin.js:8:15)
+  |     at Object.create (<root>/apps/oxlint/test/fixtures/custom_plugin_lint_create_error/plugin.ts:10:15)
 
 Found 0 warnings and 1 error.
 Finished in Xms on 1 file using X threads.
diff --git a/apps/oxlint/test/fixtures/custom_plugin_lint_create_error/plugin.js b/apps/oxlint/test/fixtures/custom_plugin_lint_create_error/plugin.ts
similarity index 59%
rename from apps/oxlint/test/fixtures/custom_plugin_lint_create_error/plugin.js
rename to apps/oxlint/test/fixtures/custom_plugin_lint_create_error/plugin.ts
index 181f5eb1f1346..515db9ff2c699 100644
--- a/apps/oxlint/test/fixtures/custom_plugin_lint_create_error/plugin.js
+++ b/apps/oxlint/test/fixtures/custom_plugin_lint_create_error/plugin.ts
@@ -1,4 +1,6 @@
-export default {
+import type { Plugin } from '../../../dist/index.js';
+
+const plugin: Plugin = {
   meta: {
     name: 'error-plugin',
   },
@@ -10,3 +12,5 @@ export default {
     },
   },
 };
+
+export default plugin;
diff --git a/apps/oxlint/test/fixtures/custom_plugin_lint_fix_error/.oxlintrc.json b/apps/oxlint/test/fixtures/custom_plugin_lint_fix_error/.oxlintrc.json
index eac0cd7034245..76b546efca906 100644
--- a/apps/oxlint/test/fixtures/custom_plugin_lint_fix_error/.oxlintrc.json
+++ b/apps/oxlint/test/fixtures/custom_plugin_lint_fix_error/.oxlintrc.json
@@ -1,5 +1,5 @@
 {
-  "jsPlugins": ["./plugin.js"],
+  "jsPlugins": ["./plugin.ts"],
   "categories": { "correctness": "off" },
   "rules": {
     "error-plugin/error": "error"
diff --git a/apps/oxlint/test/fixtures/custom_plugin_lint_fix_error/output.snap.md b/apps/oxlint/test/fixtures/custom_plugin_lint_fix_error/output.snap.md
index 77742e812a9d4..9e083dcf5055c 100644
--- a/apps/oxlint/test/fixtures/custom_plugin_lint_fix_error/output.snap.md
+++ b/apps/oxlint/test/fixtures/custom_plugin_lint_fix_error/output.snap.md
@@ -6,8 +6,8 @@
   x Error running JS plugin.
   | File path: <root>/apps/oxlint/test/fixtures/custom_plugin_lint_fix_error/files/index.js
   | Error: Whoops!
-  |     at Object.fix (<root>/apps/oxlint/test/fixtures/custom_plugin_lint_fix_error/plugin.js:14:23)
-  |     at Identifier (<root>/apps/oxlint/test/fixtures/custom_plugin_lint_fix_error/plugin.js:10:21)
+  |     at Object.fix (<root>/apps/oxlint/test/fixtures/custom_plugin_lint_fix_error/plugin.ts:16:23)
+  |     at Identifier (<root>/apps/oxlint/test/fixtures/custom_plugin_lint_fix_error/plugin.ts:12:21)
 
 Found 0 warnings and 1 error.
 Finished in Xms on 1 file using X threads.
diff --git a/apps/oxlint/test/fixtures/custom_plugin_lint_fix_error/plugin.js b/apps/oxlint/test/fixtures/custom_plugin_lint_fix_error/plugin.ts
similarity index 78%
rename from apps/oxlint/test/fixtures/custom_plugin_lint_fix_error/plugin.js
rename to apps/oxlint/test/fixtures/custom_plugin_lint_fix_error/plugin.ts
index 40903559dce79..6f87e5ff7e8fc 100644
--- a/apps/oxlint/test/fixtures/custom_plugin_lint_fix_error/plugin.js
+++ b/apps/oxlint/test/fixtures/custom_plugin_lint_fix_error/plugin.ts
@@ -1,4 +1,6 @@
-export default {
+import type { Plugin } from '../../../dist/index.js';
+
+const plugin: Plugin = {
   meta: {
     name: 'error-plugin',
   },
@@ -20,3 +22,5 @@ export default {
     },
   },
 };
+
+export default plugin;
diff --git a/apps/oxlint/test/fixtures/custom_plugin_lint_visit_error/.oxlintrc.json b/apps/oxlint/test/fixtures/custom_plugin_lint_visit_error/.oxlintrc.json
index eac0cd7034245..76b546efca906 100644
--- a/apps/oxlint/test/fixtures/custom_plugin_lint_visit_error/.oxlintrc.json
+++ b/apps/oxlint/test/fixtures/custom_plugin_lint_visit_error/.oxlintrc.json
@@ -1,5 +1,5 @@
 {
-  "jsPlugins": ["./plugin.js"],
+  "jsPlugins": ["./plugin.ts"],
   "categories": { "correctness": "off" },
   "rules": {
     "error-plugin/error": "error"
diff --git a/apps/oxlint/test/fixtures/custom_plugin_lint_visit_error/output.snap.md b/apps/oxlint/test/fixtures/custom_plugin_lint_visit_error/output.snap.md
index 6c7b09b199064..2a209e3e5b759 100644
--- a/apps/oxlint/test/fixtures/custom_plugin_lint_visit_error/output.snap.md
+++ b/apps/oxlint/test/fixtures/custom_plugin_lint_visit_error/output.snap.md
@@ -6,7 +6,7 @@
   x Error running JS plugin.
   | File path: <root>/apps/oxlint/test/fixtures/custom_plugin_lint_visit_error/files/index.js
   | Error: Whoops!
-  |     at Identifier (<root>/apps/oxlint/test/fixtures/custom_plugin_lint_visit_error/plugin.js:10:19)
+  |     at Identifier (<root>/apps/oxlint/test/fixtures/custom_plugin_lint_visit_error/plugin.ts:12:19)
 
 Found 0 warnings and 1 error.
 Finished in Xms on 1 file using X threads.
diff --git a/apps/oxlint/test/fixtures/custom_plugin_lint_visit_error/plugin.js b/apps/oxlint/test/fixtures/custom_plugin_lint_visit_error/plugin.ts
similarity index 68%
rename from apps/oxlint/test/fixtures/custom_plugin_lint_visit_error/plugin.js
rename to apps/oxlint/test/fixtures/custom_plugin_lint_visit_error/plugin.ts
index c0dbde14d618f..b02de0fc59544 100644
--- a/apps/oxlint/test/fixtures/custom_plugin_lint_visit_error/plugin.js
+++ b/apps/oxlint/test/fixtures/custom_plugin_lint_visit_error/plugin.ts
@@ -1,4 +1,6 @@
-export default {
+import type { Plugin } from '../../../dist/index.js';
+
+const plugin: Plugin = {
   meta: {
     name: 'error-plugin',
   },
@@ -14,3 +16,5 @@ export default {
     },
   },
 };
+
+export default plugin;
diff --git a/apps/oxlint/test/fixtures/custom_plugin_missing_rule/.oxlintrc.json b/apps/oxlint/test/fixtures/custom_plugin_missing_rule/.oxlintrc.json
index 81ab9e9a22252..c36bad1c7cf08 100644
--- a/apps/oxlint/test/fixtures/custom_plugin_missing_rule/.oxlintrc.json
+++ b/apps/oxlint/test/fixtures/custom_plugin_missing_rule/.oxlintrc.json
@@ -1,5 +1,5 @@
 {
-  "jsPlugins": ["./plugin.js"],
+  "jsPlugins": ["./plugin.ts"],
   "categories": { "correctness": "off" },
   "rules": {
     "basic-custom-plugin/unknown-rule": "error"
diff --git a/apps/oxlint/test/fixtures/custom_plugin_missing_rule/plugin.js b/apps/oxlint/test/fixtures/custom_plugin_missing_rule/plugin.js
deleted file mode 100644
index a2127eaac50f3..0000000000000
--- a/apps/oxlint/test/fixtures/custom_plugin_missing_rule/plugin.js
+++ /dev/null
@@ -1,6 +0,0 @@
-export default {
-  meta: {
-    name: 'basic-custom-plugin',
-  },
-  rules: {},
-};
diff --git a/apps/oxlint/test/fixtures/custom_plugin_missing_rule/plugin.ts b/apps/oxlint/test/fixtures/custom_plugin_missing_rule/plugin.ts
new file mode 100644
index 0000000000000..b7ce410eb57e2
--- /dev/null
+++ b/apps/oxlint/test/fixtures/custom_plugin_missing_rule/plugin.ts
@@ -0,0 +1,10 @@
+import type { Plugin } from '../../../dist/index.js';
+
+const plugin: Plugin = {
+  meta: {
+    name: 'basic-custom-plugin',
+  },
+  rules: {},
+};
+
+export default plugin;
diff --git a/apps/oxlint/test/fixtures/custom_plugin_via_overrides/.oxlintrc.json b/apps/oxlint/test/fixtures/custom_plugin_via_overrides/.oxlintrc.json
index e29763afcb653..33ec7bf613860 100644
--- a/apps/oxlint/test/fixtures/custom_plugin_via_overrides/.oxlintrc.json
+++ b/apps/oxlint/test/fixtures/custom_plugin_via_overrides/.oxlintrc.json
@@ -2,7 +2,7 @@
   "overrides": [
     {
       "files": ["*.js"],
-      "jsPlugins": ["./plugin.js"],
+      "jsPlugins": ["./plugin.ts"],
       "rules": {
         "basic-custom-plugin/no-debugger": "error"
       }
diff --git a/apps/oxlint/test/fixtures/basic_custom_plugin_warn_severity/plugin.js b/apps/oxlint/test/fixtures/custom_plugin_via_overrides/plugin.ts
similarity index 77%
rename from apps/oxlint/test/fixtures/basic_custom_plugin_warn_severity/plugin.js
rename to apps/oxlint/test/fixtures/custom_plugin_via_overrides/plugin.ts
index d401a98de06ee..d8f0b772b32f1 100644
--- a/apps/oxlint/test/fixtures/basic_custom_plugin_warn_severity/plugin.js
+++ b/apps/oxlint/test/fixtures/custom_plugin_via_overrides/plugin.ts
@@ -1,4 +1,6 @@
-export default {
+import type { Plugin } from '../../../dist/index.js';
+
+const plugin: Plugin = {
   meta: {
     name: 'basic-custom-plugin',
   },
@@ -17,3 +19,5 @@ export default {
     },
   },
 };
+
+export default plugin;
diff --git a/apps/oxlint/test/fixtures/custom_plugin_via_overrides_missing_rule/.oxlintrc.json b/apps/oxlint/test/fixtures/custom_plugin_via_overrides_missing_rule/.oxlintrc.json
index 05534ba871158..e04b920dd758b 100644
--- a/apps/oxlint/test/fixtures/custom_plugin_via_overrides_missing_rule/.oxlintrc.json
+++ b/apps/oxlint/test/fixtures/custom_plugin_via_overrides_missing_rule/.oxlintrc.json
@@ -5,7 +5,7 @@
   "overrides": [
     {
       "files": ["*.js"],
-      "jsPlugins": ["./plugin.js"],
+      "jsPlugins": ["./plugin.ts"],
       "rules": {
         "basic-custom-plugin/missing": "error"
       }
diff --git a/apps/oxlint/test/fixtures/custom_plugin_via_overrides_missing_rule/plugin.js b/apps/oxlint/test/fixtures/custom_plugin_via_overrides_missing_rule/plugin.js
deleted file mode 100644
index d401a98de06ee..0000000000000
--- a/apps/oxlint/test/fixtures/custom_plugin_via_overrides_missing_rule/plugin.js
+++ /dev/null
@@ -1,19 +0,0 @@
-export default {
-  meta: {
-    name: 'basic-custom-plugin',
-  },
-  rules: {
-    'no-debugger': {
-      create(context) {
-        return {
-          DebuggerStatement(debuggerStatement) {
-            context.report({
-              message: 'Unexpected Debugger Statement',
-              node: debuggerStatement,
-            });
-          },
-        };
-      },
-    },
-  },
-};
diff --git a/apps/oxlint/test/fixtures/custom_plugin_via_overrides_missing_rule/plugin.ts b/apps/oxlint/test/fixtures/custom_plugin_via_overrides_missing_rule/plugin.ts
new file mode 100644
index 0000000000000..d8f0b772b32f1
--- /dev/null
+++ b/apps/oxlint/test/fixtures/custom_plugin_via_overrides_missing_rule/plugin.ts
@@ -0,0 +1,23 @@
+import type { Plugin } from '../../../dist/index.js';
+
+const plugin: Plugin = {
+  meta: {
+    name: 'basic-custom-plugin',
+  },
+  rules: {
+    'no-debugger': {
+      create(context) {
+        return {
+          DebuggerStatement(debuggerStatement) {
+            context.report({
+              message: 'Unexpected Debugger Statement',
+              node: debuggerStatement,
+            });
+          },
+        };
+      },
+    },
+  },
+};
+
+export default plugin;
diff --git a/apps/oxlint/test/fixtures/estree/.oxlintrc.json b/apps/oxlint/test/fixtures/estree/.oxlintrc.json
index 99e39e9337d56..1212ee660e647 100644
--- a/apps/oxlint/test/fixtures/estree/.oxlintrc.json
+++ b/apps/oxlint/test/fixtures/estree/.oxlintrc.json
@@ -1,5 +1,5 @@
 {
-  "jsPlugins": ["./plugin.js"],
+  "jsPlugins": ["./plugin.ts"],
   "categories": {
     "correctness": "off"
   },
diff --git a/apps/oxlint/test/fixtures/estree/plugin.js b/apps/oxlint/test/fixtures/estree/plugin.ts
similarity index 95%
rename from apps/oxlint/test/fixtures/estree/plugin.js
rename to apps/oxlint/test/fixtures/estree/plugin.ts
index a17983811dc9a..f8c3281b75a93 100644
--- a/apps/oxlint/test/fixtures/estree/plugin.js
+++ b/apps/oxlint/test/fixtures/estree/plugin.ts
@@ -1,4 +1,6 @@
-export default {
+import type { Plugin } from '../../../dist/index.js';
+
+const plugin: Plugin = {
   meta: {
     name: 'estree-check',
   },
@@ -8,7 +10,7 @@ export default {
         // Note: Collect visits in an array instead of `context.report` in each visitor function,
         // to ensure visitation happens in right order.
         // Diagnostics may be output in different order from the order they're created in.
-        const visits = [];
+        const visits: string[] = [];
         return {
           Program(program) {
             visits.push(program.type);
@@ -78,3 +80,5 @@ export default {
     },
   },
 };
+
+export default plugin;
diff --git a/apps/oxlint/test/fixtures/fixes/.oxlintrc.json b/apps/oxlint/test/fixtures/fixes/.oxlintrc.json
index 942cdb6f10406..af50ce27d17c6 100644
--- a/apps/oxlint/test/fixtures/fixes/.oxlintrc.json
+++ b/apps/oxlint/test/fixtures/fixes/.oxlintrc.json
@@ -1,5 +1,5 @@
 {
-  "jsPlugins": ["./plugin.js"],
+  "jsPlugins": ["./plugin.ts"],
   "categories": {
     "correctness": "off"
   },
diff --git a/apps/oxlint/test/fixtures/fixes/plugin.js b/apps/oxlint/test/fixtures/fixes/plugin.ts
similarity index 93%
rename from apps/oxlint/test/fixtures/fixes/plugin.js
rename to apps/oxlint/test/fixtures/fixes/plugin.ts
index 1353436b25a1f..07c7a4d9172f7 100644
--- a/apps/oxlint/test/fixtures/fixes/plugin.js
+++ b/apps/oxlint/test/fixtures/fixes/plugin.ts
@@ -1,4 +1,6 @@
-export default {
+import type { Diagnostic, Plugin, Range } from '../../../dist/index.js';
+
+const plugin: Plugin = {
   meta: {
     name: 'fixes-plugin',
   },
@@ -14,7 +16,7 @@ export default {
             debuggerCount++;
 
             let thisIsReport;
-            const report = {
+            const report: Diagnostic = {
               message: 'Remove debugger statement',
               node,
               fix(fixer) {
@@ -96,7 +98,7 @@ export default {
                   node,
                   fix(fixer) {
                     // Fixes can be in any order
-                    const range = [node.start, node.end];
+                    const range: Range = [node.start, node.end];
                     return [
                       fixer.replaceTextRange(range, 'er'),
                       fixer.insertTextAfterRange(range, 'mouse'),
@@ -122,7 +124,7 @@ export default {
                   // `fix` can be a generator function
                   *fix(fixer) {
                     // Fixes can be in any order
-                    const range = [node.start, node.end];
+                    const range: Range = [node.start, node.end];
                     yield fixer.insertTextAfterRange(range, 'bunga');
                     yield fixer.replaceTextRange(range, 'a');
                     yield fixer.insertTextBeforeRange(range, 'cow');
@@ -135,3 +137,5 @@ export default {
     },
   },
 };
+
+export default plugin;
diff --git a/apps/oxlint/test/fixtures/utf16_offsets/.oxlintrc.json b/apps/oxlint/test/fixtures/utf16_offsets/.oxlintrc.json
index d6d8cf1b9d86c..40346ec859190 100644
--- a/apps/oxlint/test/fixtures/utf16_offsets/.oxlintrc.json
+++ b/apps/oxlint/test/fixtures/utf16_offsets/.oxlintrc.json
@@ -1,5 +1,5 @@
 {
-  "jsPlugins": ["./plugin.js"],
+  "jsPlugins": ["./plugin.ts"],
   "rules": {
     "utf16-plugin/no-debugger": "error"
   }
diff --git a/apps/oxlint/test/fixtures/utf16_offsets/plugin.js b/apps/oxlint/test/fixtures/utf16_offsets/plugin.ts
similarity index 78%
rename from apps/oxlint/test/fixtures/utf16_offsets/plugin.js
rename to apps/oxlint/test/fixtures/utf16_offsets/plugin.ts
index 6527efeea66e8..c064988b3e7c1 100644
--- a/apps/oxlint/test/fixtures/utf16_offsets/plugin.js
+++ b/apps/oxlint/test/fixtures/utf16_offsets/plugin.ts
@@ -1,4 +1,6 @@
-export default {
+import type { Plugin } from '../../../dist/index.js';
+
+const plugin: Plugin = {
   meta: {
     name: 'utf16-plugin',
   },
@@ -17,3 +19,5 @@ export default {
     },
   },
 };
+
+export default plugin;