diff --git a/apps/backend/src/index.ts b/apps/backend/src/index.ts
index 446051a..c1238bf 100644
--- a/apps/backend/src/index.ts
+++ b/apps/backend/src/index.ts
@@ -1,206 +1,17 @@
 import { Elysia, t } from "elysia";
 import config from "../config.toml";
-import { S3Client } from "bun";
-import {
-  HeadObjectCommand,
-  PutObjectCommand,
-  S3Client as AwsS3Client,
-} from "@aws-sdk/client-s3";
 import * as mongoose from "mongoose";
 import openapi from "@elysiajs/openapi";
+import { MediaUpload } from "@/models/media";
+import { Tag } from "@/models/tag";
+import { checkTweetData, fetchTweetData } from "./lib/tweet";
+import { makeS3FileName, s3Client, uploadToS3 } from "./lib/s3";
+import { normalizeQueryTags, normalizeTags } from "./lib/tag";
 
 await mongoose.connect(config.mongodb.uri);
 
-const mediaUploadSchema = new mongoose.Schema({
-  tweetId: { type: String, required: true },
-  tweet: { type: Object, required: true },
-  mediaIndex: { type: Number, required: true },
-  mediaUrl: { type: String, required: true },
-  s3Key: { type: String, required: true },
-  tags: { type: [String], default: [] },
-  author: { type: String, required: true },
-}, {
-  timestamps: true,
-});
-
-const tagSchema = new mongoose.Schema({
-  name: { type: String, required: true, unique: true },
-  usageCount: { type: Number, default: 0 },
-  lastUsedAt: { type: Date, default: Date.now },
-}, {
-  timestamps: true,
-});
-
-const MediaUpload = mongoose.models.MediaUpload || mongoose.model("MediaUpload", mediaUploadSchema);
-const Tag = mongoose.models.Tag || mongoose.model("Tag", tagSchema);
 const inFlightUploads = new Set<string>();
 
-const client = new S3Client({
-  accessKeyId: config.s3.access_key,
-  secretAccessKey: config.s3.secret_key,
-  bucket: config.s3.bucket,
-  endpoint: config.s3.endpoint,
-});
-
-const awsClient = new AwsS3Client({
-  region: "auto",
-  endpoint: config.s3.endpoint,
-  forcePathStyle: true,
-  credentials: {
-    accessKeyId: config.s3.access_key,
-    secretAccessKey: config.s3.secret_key,
-  },
-});
-
-async function checkTweetData(url: string, selected: Array<boolean>) {
-  // get tweet id from url
-  const match = url.match(/\/status\/(\d+)/);
-  if (!match) {
-    throw new Error("Invalid tweet URL");
-  }
-  const tweetId = match[1];
-  // find in mongodb if there is already a record with the same tweet id and media index in selected
-  const existing = await MediaUpload.findOne({ tweetId, mediaIndex: { $in: selected.map((s, i) => s ? i : -1).filter(i => i >= 0) } });
-  if (existing) {
-    return true;
-  }
-  return null;
-}
-
-async function fetchTweetData(url: string) {
-  const apiUrl = `https://api.fxtwitter.com/${url.replace(/^https?:\/\/(www\.)?(x\.com|twitter\.com|fxtwitter\.com|fixupx\.com|vxwitter\.com)\//, "")}`;
-  const response = await fetch(apiUrl);
-  if (response.ok) {
-    // const dataText = await response.text();
-    // console.log("Raw API response:", dataText);
-    const data = await response.json();
-    return data;
-  } else {
-    throw new Error(`Failed to fetch tweet data: ${response.status} ${response.statusText}`);
-  }
-}
-
-function makeS3FileName(authorId: string, tweetId: string, mediaUrl: string, index: number) {
-  const rawName = mediaUrl.split("/").pop() || `media_${Date.now()}_${index}`;
-  const withoutQuery = rawName.split("?")[0]?.split("#")[0] || `media_${Date.now()}_${index}`;
-  const safeName = withoutQuery.replace(/[^a-zA-Z0-9._-]/g, "_");
-  return `twitter/${authorId}/${tweetId}/${safeName || `media_${Date.now()}_${index}`}`;
-}
-
-async function uploadToS3WithRetry(fileName: string, mediaUrl: string, maxRetry = 3) {
-  async function existsInS3(key: string) {
-    try {
-      return await client.exists(key);
-    } catch {
-      try {
-        await awsClient.send(new HeadObjectCommand({
-          Bucket: config.s3.bucket,
-          Key: key,
-        }));
-        return true;
-      } catch {
-        return false;
-      }
-    }
-  }
-
-  async function writeToS3(key: string, body: Uint8Array, mediaType?: string | null) {
-    try {
-      await client.write(key, body);
-      return;
-    } catch (bunWriteError) {
-      console.warn(`[S3 bun write failed, fallback to aws-sdk] key=${key}`, bunWriteError);
-      await awsClient.send(new PutObjectCommand({
-        Bucket: config.s3.bucket,
-        Key: key,
-        Body: body,
-        ContentType: mediaType ?? undefined,
-      }));
-    }
-  }
-
-  async function recoverByPollingExists(reason: string) {
-    for (let probe = 1; probe <= 4; probe++) {
-      await Bun.sleep(probe * 600);
-      try {
-        if (await existsInS3(fileName)) {
-          console.warn(`[S3 upload recovered-${reason}] key=${fileName} probe=${probe}`);
-          return true;
-        }
-      } catch (existsError) {
-        console.error(`[S3 exists probe failed] key=${fileName} probe=${probe}`, existsError);
-      }
-    }
-
-    return false;
-  }
-
-  let lastError: unknown;
-
-  for (let attempt = 1; attempt <= maxRetry; attempt++) {
-    try {
-      const response = await fetch(mediaUrl);
-      if (!response.ok) {
-        throw new Error(`Failed to fetch media from ${mediaUrl}: ${response.status} ${response.statusText}`);
-      }
-
-      const arrayBuffer = await response.arrayBuffer();
-      const buffer = Buffer.from(arrayBuffer);
-      await writeToS3(fileName, buffer, response.headers.get("content-type"));
-      return;
-    } catch (error) {
-      lastError = error;
-      console.error(`[S3 upload attempt ${attempt}/${maxRetry}] key=${fileName} url=${mediaUrl}`, error);
-
-      const errorCode =
-        typeof error === "object" && error !== null && "code" in error
-          ? String((error as { code?: unknown }).code)
-          : "";
-
-      // Some S3 providers return UnknownError even when the object is eventually persisted.
-      if (errorCode === "UnknownError") {
-        if (await recoverByPollingExists("unknown")) {
-          return;
-        }
-      }
-
-      if (attempt < maxRetry) {
-        await Bun.sleep(attempt * 800);
-      }
-    }
-  }
-
-  // Final guard: do one last exists check before surfacing failure.
-  if (await recoverByPollingExists("final")) {
-    return;
-  }
-
-  throw lastError;
-}
-
-function normalizeTags(tags: string[]) {
-  const unique = new Set(
-    tags
-      .map((tag) => tag.trim())
-      .filter((tag) => tag.length > 0),
-  );
-
-  if (unique.size === 0) {
-    return ["미분류"];
-  }
-
-  return Array.from(unique);
-}
-
-function normalizeQueryTags(tags?: string | string[]) {
-  if (!tags) {
-    return [];
-  }
-
-  const rawTags = Array.isArray(tags) ? tags : [tags];
-  return normalizeTags(rawTags);
-}
-
 function buildUploadKey(url: string, selected: boolean[]) {
   const match = url.match(/\/status\/(\d+)/);
   const tweetId = match?.[1] ?? url;
@@ -315,10 +126,10 @@ const app = new Elysia()
               const fileName = makeS3FileName(tweetData.tweet.author.id, tweetData.tweet.id, url, index);
 
               try {
-                if (await client.exists(fileName)) {
+                if (await s3Client.exists(fileName)) {
                   console.log(`File ${fileName} already exists in S3, skipping upload.`);
                 } else {
-                  await uploadToS3WithRetry(fileName, url);
+                  await uploadToS3(fileName, url);
                   console.log(`Uploaded ${fileName} to S3`);
                 }
 
@@ -327,7 +138,6 @@ const app = new Elysia()
 
                 await MediaUpload.create({
                   type: "twitter",
-                  tweetId: tweetData.tweet.id,
                   tweet: tweetWithoutMedia,
                   mediaIndex: index,
                   mediaUrl: `${config.s3.endpoint}/${config.s3.bucket}/${fileName}`,
diff --git a/apps/backend/src/lib/s3.ts b/apps/backend/src/lib/s3.ts
new file mode 100644
index 0000000..6fbc088
--- /dev/null
+++ b/apps/backend/src/lib/s3.ts
@@ -0,0 +1,124 @@
+import { S3Client } from "bun";
+import {
+  HeadObjectCommand,
+  PutObjectCommand,
+  S3Client as AwsS3Client,
+} from "@aws-sdk/client-s3";
+import config from "@/../config.toml";
+
+const client = new S3Client({
+  accessKeyId: config.s3.access_key,
+  secretAccessKey: config.s3.secret_key,
+  bucket: config.s3.bucket,
+  endpoint: config.s3.endpoint,
+});
+
+const awsClient = new AwsS3Client({
+  region: "auto",
+  endpoint: config.s3.endpoint,
+  forcePathStyle: true,
+  credentials: {
+    accessKeyId: config.s3.access_key,
+    secretAccessKey: config.s3.secret_key,
+  },
+});
+
+function makeS3FileName(authorId: string, tweetId: string, mediaUrl: string, index: number) {
+  const rawName = mediaUrl.split("/").pop() || `media_${Date.now()}_${index}`;
+  const withoutQuery = rawName.split("?")[0]?.split("#")[0] || `media_${Date.now()}_${index}`;
+  const safeName = withoutQuery.replace(/[^a-zA-Z0-9._-]/g, "_");
+  return `twitter/${authorId}/${tweetId}/${safeName || `media_${Date.now()}_${index}`}`;
+}
+
+async function uploadToS3(fileName: string, mediaUrl: string, maxRetry = 3) {
+  async function existsInS3(key: string) {
+    try {
+      return await client.exists(key);
+    } catch {
+      try {
+        await awsClient.send(new HeadObjectCommand({
+          Bucket: config.s3.bucket,
+          Key: key,
+        }));
+        return true;
+      } catch {
+        return false;
+      }
+    }
+  }
+
+  async function writeToS3(key: string, body: Uint8Array, mediaType?: string | null) {
+    try {
+      await client.write(key, body);
+      return;
+    } catch (bunWriteError) {
+      console.warn(`[S3 bun write failed, fallback to aws-sdk] key=${key}`, bunWriteError);
+      await awsClient.send(new PutObjectCommand({
+        Bucket: config.s3.bucket,
+        Key: key,
+        Body: body,
+        ContentType: mediaType ?? undefined,
+      }));
+    }
+  }
+
+  async function recoverByPollingExists(reason: string) {
+    for (let probe = 1; probe <= 4; probe++) {
+      await Bun.sleep(probe * 600);
+      try {
+        if (await existsInS3(fileName)) {
+          console.warn(`[S3 upload recovered-${reason}] key=${fileName} probe=${probe}`);
+          return true;
+        }
+      } catch (existsError) {
+        console.error(`[S3 exists probe failed] key=${fileName} probe=${probe}`, existsError);
+      }
+    }
+
+    return false;
+  }
+
+  let lastError: unknown;
+
+  for (let attempt = 1; attempt <= maxRetry; attempt++) {
+    try {
+      const response = await fetch(mediaUrl);
+      if (!response.ok) {
+        throw new Error(`Failed to fetch media from ${mediaUrl}: ${response.status} ${response.statusText}`);
+      }
+
+      const arrayBuffer = await response.arrayBuffer();
+      const buffer = Buffer.from(arrayBuffer);
+      await writeToS3(fileName, buffer, response.headers.get("content-type"));
+      return;
+    } catch (error) {
+      lastError = error;
+      console.error(`[S3 upload attempt ${attempt}/${maxRetry}] key=${fileName} url=${mediaUrl}`, error);
+
+      const errorCode =
+        typeof error === "object" && error !== null && "code" in error
+          ? String((error as { code?: unknown }).code)
+          : "";
+
+      // Some S3 providers return UnknownError even when the object is eventually persisted.
+      if (errorCode === "UnknownError") {
+        if (await recoverByPollingExists("unknown")) {
+          return;
+        }
+      }
+
+      if (attempt < maxRetry) {
+        await Bun.sleep(attempt * 800);
+      }
+    }
+  }
+
+  // Final guard: do one last exists check before surfacing failure.
+  if (await recoverByPollingExists("final")) {
+    return;
+  }
+
+  throw lastError;
+}
+
+export { makeS3FileName, uploadToS3, client as s3Client };
\ No newline at end of file
diff --git a/apps/backend/src/lib/tag.ts b/apps/backend/src/lib/tag.ts
new file mode 100644
index 0000000..9c6f02c
--- /dev/null
+++ b/apps/backend/src/lib/tag.ts
@@ -0,0 +1,25 @@
+function normalizeTags(tags: string[]) {
+  const unique = new Set(
+    tags
+      .map((tag) => tag.trim())
+      .filter((tag) => tag.length > 0),
+  );
+
+  if (unique.size === 0) {
+    return ["미분류"];
+  }
+
+  return Array.from(unique);
+}
+
+function normalizeQueryTags(tags?: string | string[]) {
+  if (!tags) {
+    return [];
+  }
+
+  const rawTags = Array.isArray(tags) ? tags : [tags];
+  return normalizeTags(rawTags);
+}
+
+
+export { normalizeTags, normalizeQueryTags };
\ No newline at end of file
diff --git a/apps/backend/src/lib/tweet.ts b/apps/backend/src/lib/tweet.ts
new file mode 100644
index 0000000..baee3ab
--- /dev/null
+++ b/apps/backend/src/lib/tweet.ts
@@ -0,0 +1,31 @@
+import { MediaUpload } from "@/models/media";
+
+async function checkTweetData(url: string, selected: Array<boolean>) {
+  // get tweet id from url
+  const match = url.match(/\/status\/(\d+)/);
+  if (!match) {
+    throw new Error("Invalid tweet URL");
+  }
+  const tweetId = match[1];
+  // find in mongodb if there is already a record with the same tweet id and media index in selected
+  const existing = await MediaUpload.findOne({ "tweetData.tweet.id": tweetId, mediaIndex: { $in: selected.map((s, i) => s ? i : -1).filter(i => i >= 0) } });
+  if (existing) {
+    return true;
+  }
+  return null;
+}
+
+async function fetchTweetData(url: string) {
+  const apiUrl = `https://api.fxtwitter.com/${url.replace(/^https?:\/\/(www\.)?(x\.com|twitter\.com|fxtwitter\.com|fixupx\.com|vxwitter\.com)\//, "")}`;
+  const response = await fetch(apiUrl);
+  if (response.ok) {
+    // const dataText = await response.text();
+    // console.log("Raw API response:", dataText);
+    const data = await response.json();
+    return data;
+  } else {
+    throw new Error(`Failed to fetch tweet data: ${response.status} ${response.statusText}`);
+  }
+}
+
+export { checkTweetData, fetchTweetData };
\ No newline at end of file
diff --git a/apps/backend/src/models/media.ts b/apps/backend/src/models/media.ts
new file mode 100644
index 0000000..cf735cf
--- /dev/null
+++ b/apps/backend/src/models/media.ts
@@ -0,0 +1,20 @@
+import * as mongoose from "mongoose";
+
+const mediaUploadSchema = new mongoose.Schema({
+  type: { type: String, required: true },
+  tweet: {
+    type: Object,
+    required: function (this: { type?: string }) {
+      return this.type === "twitter";
+    },
+  },
+  mediaIndex: { type: Number, required: true },
+  mediaUrl: { type: String, required: true },
+  s3Key: { type: String, required: true },
+  tags: { type: [String], default: [] },
+  author: { type: String, required: true },
+}, {
+  timestamps: true,
+});
+
+export const MediaUpload = mongoose.model("MediaUpload", mediaUploadSchema);
\ No newline at end of file
diff --git a/apps/backend/src/models/tag.ts b/apps/backend/src/models/tag.ts
new file mode 100644
index 0000000..e6d2280
--- /dev/null
+++ b/apps/backend/src/models/tag.ts
@@ -0,0 +1,11 @@
+import * as mongoose from "mongoose";
+
+const tagSchema = new mongoose.Schema({
+  name: { type: String, required: true, unique: true },
+  usageCount: { type: Number, default: 0 },
+  lastUsedAt: { type: Date, default: Date.now },
+}, {
+  timestamps: true,
+});
+
+export const Tag = mongoose.model("Tag", tagSchema);
\ No newline at end of file
diff --git a/apps/backend/tsconfig.json b/apps/backend/tsconfig.json
index 1ca2350..987cde1 100644
--- a/apps/backend/tsconfig.json
+++ b/apps/backend/tsconfig.json
@@ -28,8 +28,11 @@
     "module": "ES2022",                                /* Specify what module code is generated. */
     // "rootDir": "./",                                  /* Specify the root folder within your source files. */
     "moduleResolution": "node",                       /* Specify how TypeScript looks up a file from a given module specifier. */
-    // "baseUrl": "./",                                  /* Specify the base directory to resolve non-relative module names. */
+    "baseUrl": "./",                                  /* Specify the base directory to resolve non-relative module names. */
     // "paths": {},                                      /* Specify a set of entries that re-map imports to additional lookup locations. */
+    "paths": {
+      "@/*": ["./src/*"]
+    },
     // "rootDirs": [],                                   /* Allow multiple folders to be treated as one when resolving modules. */
     // "typeRoots": [],                                  /* Specify multiple folders that act like './node_modules/@types'. */
     "types": ["bun-types"],                                      /* Specify type package names to be included without being referenced in a source file. */