diff --git a/src/index.ts b/src/index.ts
--- a/src/index.ts	2024-01-29 17:00:00.000000000 +0000
+++ b/src/index.ts	2024-01-29 17:00:00.000000000 +0000
@@ -25,6 +25,14 @@
   branch?: string;
 }
 
+interface UpdateFileArgs extends RepoArgs {
+  path: string;
+  content: string;
+  message: string;
+  branch?: string;
+  sha: string;
+}
+
 interface GetContentsArgs extends RepoArgs {
   path: string;
   ref?: string;
@@ -214,6 +222,41 @@
             required: ['owner', 'repo', 'path', 'message'],
           },
         },
+        {
+          name: 'update_file',
+          description: 'Update an existing file in a repository',
+          inputSchema: {
+            type: 'object',
+            properties: {
+              owner: {
+                type: 'string',
+                description: 'Repository owner',
+              },
+              repo: {
+                type: 'string',
+                description: 'Repository name',
+              },
+              path: {
+                type: 'string',
+                description: 'Path to file',
+              },
+              content: {
+                type: 'string',
+                description: 'New file content (will be base64 encoded)',
+              },
+              message: {
+                type: 'string',
+                description: 'Commit message',
+              },
+              branch: {
+                type: 'string',
+                description: 'Branch name',
+              },
+              sha: {
+                type: 'string',
+                description: 'SHA of the file being replaced',
+              },
+            },
+            required: ['owner', 'repo', 'path', 'content', 'message', 'sha'],
+          },
+        },
         {
           name: 'create_branch',
           description: 'Create a new branch in a repository',
@@ -432,6 +475,41 @@
             };
           }
 
+          case 'update_file': {
+            const args = request.params.arguments as unknown as UpdateFileArgs;
+            const response = await this.api.put(
+              `/repos/${args.owner}/${args.repo}/contents/${args.path}`,
+              {
+                content: Buffer.from(args.content).toString('base64'),
+                message: args.message,
+                sha: args.sha,
+                branch: args.branch,
+              }
+            );
+
+            // Verify the file after update
+            const verifyResponse = await this.api.get(
+              `/repos/${args.owner}/${args.repo}/contents/${args.path}`,
+              {
+                params: { ref: args.branch },
+              }
+            );
+
+            return {
+              content: [
+                {
+                  type: 'text',
+                  text: JSON.stringify({
+                    success: true,
+                    message: 'File updated successfully',
+                    file: {
+                      path: args.path,
+                      commit: response.data.commit,
+                    },
+                    content: verifyResponse.data,
+                  }, null, 2),
+                },
+              ],
+            };
+          }
+
           case 'create_branch': {
             const { owner, repo, branch, from } = request.params.arguments as unknown as CreateBranchArgs;