diff --git a/README.md b/README.md
index df16ee4..8c66f6a 100644
--- a/README.md
+++ b/README.md
@@ -31,6 +31,7 @@ jobs:
 | `failure-level` | The lowest annotation level to fail on ("warning or "error"") | no | `"error"` |
 | `conclusion-level` | Action conclusion ("success" or "failure") if annotations of the failure-level were created. | no | `"success"` |
 | `working-directory` | Which directory to run the action in | no | `"."` |
+| `extensions` | A comma separated list of extensions to run ESLint on. | no | `".js,.ts,.jsx,.tsx,.mjs,.cjs"` |
 
 ## Outputs
 
diff --git a/action.yml b/action.yml
index f3f1ce8..e3c797b 100644
--- a/action.yml
+++ b/action.yml
@@ -19,6 +19,10 @@ inputs:
     description: Which directory to run the action in
     required: false
     default: "."
+  extensions:
+    description: A comma separated list of extensions to run ESLint on.
+    required: false
+    default: ".js,.ts,.jsx,.tsx,.mjs,.cjs"
 outputs:
   warning-count:
     description: "Number of relevant warnings found"
diff --git a/dist/index.js b/dist/index.js
index c4c19e8..74e822d 100644
--- a/dist/index.js
+++ b/dist/index.js
@@ -26176,7 +26176,7 @@ var __importStar = (this && this.__importStar) || function (mod) {
     return result;
 };
 Object.defineProperty(exports, "__esModule", ({ value: true }));
-exports.EslintResult = void 0;
+exports.ESLintResult = void 0;
 const core = __importStar(__nccwpck_require__(2186));
 const git_utils_1 = __nccwpck_require__(5601);
 var Severity;
@@ -26184,7 +26184,7 @@ var Severity;
     Severity[Severity["Warning"] = 1] = "Warning";
     Severity[Severity["Error"] = 2] = "Error";
 })(Severity || (Severity = {}));
-class EslintResult {
+class ESLintResult {
     relevantWarningCount = 0;
     relevantErrorCount = 0;
     resultObject;
@@ -26192,7 +26192,7 @@ class EslintResult {
     relevantMessages = [];
     static async for(resultObject, compareSha) {
         const changeRanges = await (0, git_utils_1.generateChangeRanges)(resultObject.filePath, compareSha);
-        return new EslintResult(resultObject, changeRanges);
+        return new ESLintResult(resultObject, changeRanges);
     }
     constructor(resultObject, changeRanges) {
         this.resultObject = resultObject;
@@ -26247,7 +26247,7 @@ class EslintResult {
         return this.resultObject.filePath.replace(absoluteFolderPath, "");
     }
 }
-exports.EslintResult = EslintResult;
+exports.ESLintResult = ESLintResult;
 
 
 /***/ }),
@@ -26363,13 +26363,21 @@ async function run() {
         changedFiles = await (0, git_utils_1.detectChangedFiles)(compareSha);
     }
     core.debug(`Changed files: ${changedFiles}`);
-    let { stdout: eslintOut, exitCode } = await (0, exec_1.getExecOutput)("npx eslint --format=json", changedFiles, 
+    let extensions = core.getInput("extensions").split(",");
+    core.debug(`Extensions: ${extensions}`);
+    let changedFilesMatchingExtensions = changedFiles.filter((file) => extensions.some((ext) => file.endsWith(ext)));
+    core.debug(`Changed files matching extensions: ${changedFilesMatchingExtensions}`);
+    // Bail out early if the file list is empty (older ESLint versions will
+    // complain if the list is empty)
+    if (changedFilesMatchingExtensions.length === 0)
+        return;
+    let { stdout: eslintOut, exitCode } = await (0, exec_1.getExecOutput)("npx eslint --format=json", changedFilesMatchingExtensions, 
     // Eslint will return exit code 1 if it finds linting problems, but that is
     // expected and we don't want to stop execution because of it.
     { ignoreReturnCode: true });
     let eslintJson = JSON.parse(eslintOut);
     core.debug(`Eslint exit code: ${exitCode}`);
-    let promises = eslintJson.map((resultObject) => eslint_result_1.EslintResult.for(resultObject, compareSha));
+    let promises = eslintJson.map((resultObject) => eslint_result_1.ESLintResult.for(resultObject, compareSha));
     let eslintResults = await Promise.all(promises);
     core.debug("Eslint results ->");
     eslintResults.forEach((result) => core.debug(JSON.stringify(result)));
diff --git a/src/eslint_result.ts b/src/eslint_result.ts
index 281cfb1..62c7b4e 100644
--- a/src/eslint_result.ts
+++ b/src/eslint_result.ts
@@ -3,10 +3,10 @@ import { ChangeRange, generateChangeRanges } from "./git_utils"
 
 export type ResultObject = {
   filePath: string
-  messages: EslintMessage[]
+  messages: ESLintMessage[]
 }
 
-type EslintMessage = {
+type ESLintMessage = {
   ruleId: string
   severity: Severity
   message: string
@@ -24,22 +24,22 @@ enum Severity {
   Error = 2,
 }
 
-export class EslintResult {
+export class ESLintResult {
   public relevantWarningCount: number = 0
   public relevantErrorCount: number = 0
   private resultObject: ResultObject
   private changeRanges: ChangeRange[]
-  private relevantMessages: EslintMessage[] = []
+  private relevantMessages: ESLintMessage[] = []
 
   static async for(
     resultObject: ResultObject,
     compareSha: string,
-  ): Promise<EslintResult> {
+  ): Promise<ESLintResult> {
     const changeRanges = await generateChangeRanges(
       resultObject.filePath,
       compareSha,
     )
-    return new EslintResult(resultObject, changeRanges)
+    return new ESLintResult(resultObject, changeRanges)
   }
 
   constructor(resultObject: ResultObject, changeRanges: ChangeRange[]) {
diff --git a/src/index.ts b/src/index.ts
index b13f017..cd80156 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,7 +1,7 @@
 import * as core from "@actions/core"
 import { detectChangedFiles, detectChangedFilesInFolder } from "./git_utils"
 import { getExecOutput } from "@actions/exec"
-import { ResultObject, EslintResult } from "./eslint_result"
+import { ResultObject, ESLintResult } from "./eslint_result"
 
 async function run() {
   let workingDirectory = core.getInput("working-directory")
@@ -34,9 +34,22 @@ async function run() {
 
   core.debug(`Changed files: ${changedFiles}`)
 
+  let extensions = core.getInput("extensions").split(",")
+  core.debug(`Extensions: ${extensions}`)
+  let changedFilesMatchingExtensions = changedFiles.filter((file) =>
+    extensions.some((ext) => file.endsWith(ext)),
+  )
+  core.debug(
+    `Changed files matching extensions: ${changedFilesMatchingExtensions}`,
+  )
+
+  // Bail out early if the file list is empty (older ESLint versions will
+  // complain if the list is empty)
+  if (changedFilesMatchingExtensions.length === 0) return
+
   let { stdout: eslintOut, exitCode } = await getExecOutput(
     "npx eslint --format=json",
-    changedFiles,
+    changedFilesMatchingExtensions,
     // Eslint will return exit code 1 if it finds linting problems, but that is
     // expected and we don't want to stop execution because of it.
     { ignoreReturnCode: true },
@@ -44,8 +57,8 @@ async function run() {
   let eslintJson = JSON.parse(eslintOut)
   core.debug(`Eslint exit code: ${exitCode}`)
 
-  let promises: Array<Promise<EslintResult>> = eslintJson.map(
-    (resultObject: ResultObject) => EslintResult.for(resultObject, compareSha),
+  let promises: Array<Promise<ESLintResult>> = eslintJson.map(
+    (resultObject: ResultObject) => ESLintResult.for(resultObject, compareSha),
   )
   let eslintResults = await Promise.all(promises)
 
diff --git a/test/pull_request_event_payload.json b/test/pull_request_event_payload.json
index dde140b..904c5b5 100644
--- a/test/pull_request_event_payload.json
+++ b/test/pull_request_event_payload.json
@@ -1 +1 @@
-{ "pull_request": { "base": { "sha": "c2eaebd173390cb17efa35fce4d4941ccd5b3b5c" } } }
+{ "pull_request": { "base": { "sha": "54de0dbcb922b6544025d1604d46146fcbdbda81" } } }
diff --git a/test/snapshots/updates/some_file_that_eslint_should_ignore b/test/snapshots/updates/some_file_that_eslint_should_ignore
index e69de29..27921aa 100644
--- a/test/snapshots/updates/some_file_that_eslint_should_ignore
+++ b/test/snapshots/updates/some_file_that_eslint_should_ignore
@@ -0,0 +1,4 @@
+class EslintShouldIgnoreThis
+    def evenThoughItsWeird (*)
+ end
+ end
diff --git a/test/v6/some_file_that_eslint_should_ignore b/test/v6/some_file_that_eslint_should_ignore
index e69de29..27921aa 100644
--- a/test/v6/some_file_that_eslint_should_ignore
+++ b/test/v6/some_file_that_eslint_should_ignore
@@ -0,0 +1,4 @@
+class EslintShouldIgnoreThis
+    def evenThoughItsWeird (*)
+ end
+ end
diff --git a/test/v7/some_file_that_eslint_should_ignore b/test/v7/some_file_that_eslint_should_ignore
index e69de29..27921aa 100644
--- a/test/v7/some_file_that_eslint_should_ignore
+++ b/test/v7/some_file_that_eslint_should_ignore
@@ -0,0 +1,4 @@
+class EslintShouldIgnoreThis
+    def evenThoughItsWeird (*)
+ end
+ end
diff --git a/test/v8/some_file_that_eslint_should_ignore b/test/v8/some_file_that_eslint_should_ignore
index e69de29..27921aa 100644
--- a/test/v8/some_file_that_eslint_should_ignore
+++ b/test/v8/some_file_that_eslint_should_ignore
@@ -0,0 +1,4 @@
+class EslintShouldIgnoreThis
+    def evenThoughItsWeird (*)
+ end
+ end
diff --git a/test/v9/some_file_that_eslint_should_ignore b/test/v9/some_file_that_eslint_should_ignore
index e69de29..27921aa 100644
--- a/test/v9/some_file_that_eslint_should_ignore
+++ b/test/v9/some_file_that_eslint_should_ignore
@@ -0,0 +1,4 @@
+class EslintShouldIgnoreThis
+    def evenThoughItsWeird (*)
+ end
+ end