diff --git a/builder/src/components/DragDropFileInput.tsx b/builder/src/components/DragDropFileInput.tsx
index 3456e316f..3f446cf82 100644
--- a/builder/src/components/DragDropFileInput.tsx
+++ b/builder/src/components/DragDropFileInput.tsx
@@ -1,13 +1,19 @@
-import React, { CSSProperties, useEffect, useRef, useState } from "react";
+import React, {
+    CSSProperties,
+    MutableRefObject,
+    useEffect,
+    useState,
+} from "react";
 
 interface DragDropFileInputProps {
     title: string;
     onChange?: (files: FileList) => void;
     readonly?: boolean;
+    fileInputRef: MutableRefObject<HTMLInputElement | null>;
 }
 
 export const DragDropFileInput: React.FC<DragDropFileInputProps> = (props) => {
-    const fileInputRef = useRef<HTMLInputElement>(null);
+    const fileInput = props.fileInputRef.current;
     const [fileDropStyle, setFileDropStyle] = useState<CSSProperties>({});
     const [lastTarget, setLastTarget] = useState<EventTarget | null>(null);
     const [isDragging, setIsDragging] = useState<boolean>(false);
@@ -39,8 +45,7 @@ export const DragDropFileInput: React.FC<DragDropFileInputProps> = (props) => {
     };
     const fileChange = () => {
         if (!props.readonly) {
-            const inp = fileInputRef.current;
-            const files = inp?.files;
+            const files = fileInput?.files;
             if (props.onChange && files) {
                 props.onChange(files);
             }
@@ -49,9 +54,8 @@ export const DragDropFileInput: React.FC<DragDropFileInputProps> = (props) => {
     };
     const onDrop = (e: React.DragEvent) => {
         if (!props.readonly) {
-            const inp = fileInputRef.current;
-            if (inp) {
-                inp.files = e.dataTransfer.files;
+            if (fileInput) {
+                fileInput.files = e.dataTransfer.files;
             }
             if (props.onChange) {
                 props.onChange(e.dataTransfer.files);
@@ -92,7 +96,7 @@ export const DragDropFileInput: React.FC<DragDropFileInputProps> = (props) => {
                 type="file"
                 name="newfile"
                 style={{ display: "none" }}
-                ref={fileInputRef}
+                ref={props.fileInputRef}
                 onChange={fileChange}
                 disabled={props.readonly}
             />
diff --git a/builder/src/upload.tsx b/builder/src/upload.tsx
index eea5b6f92..916cb7754 100644
--- a/builder/src/upload.tsx
+++ b/builder/src/upload.tsx
@@ -1,5 +1,5 @@
 import * as Sentry from "@sentry/browser";
-import React, { useEffect, useState } from "react";
+import React, { useRef, useEffect, useState } from "react";
 import {
     Community,
     ExperimentalApi,
@@ -19,6 +19,7 @@ import { FormSelectField } from "./components/FormSelectField";
 import { CommunityCategorySelector } from "./components/CommunitySelector";
 import { FormRow } from "./components/FormRow";
 import { SubmitPackage } from "./api/packageSubmit";
+import { validateZip } from "./uploadZipValidation";
 
 function getUploadProgressBarcolor(uploadStatus: FileUploadStatus | undefined) {
     if (uploadStatus == FileUploadStatus.CANCELED) {
@@ -42,17 +43,16 @@ function getSubmissionProgressBarcolor(
     return "bg-warning";
 }
 
-class FormErrors {
-    fileError: string | null = null;
+export class FormErrors {
     teamError: string | null = null;
     communitiesError: string | null = null;
     categoriesError: string | null = null;
     nsfwError: string | null = null;
     generalErrors: string[] = [];
+    fileErrors: string[] = [];
 
     get hasErrors(): boolean {
         return !(
-            this.fileError == null &&
             this.teamError == null &&
             this.communitiesError == null &&
             this.categoriesError == null &&
@@ -81,6 +81,7 @@ const SubmissionForm: React.FC<SubmissionFormProps> = observer((props) => {
     const [formErrors, setFormErrors] = useState<FormErrors>(new FormErrors());
     const [file, setFile] = useState<File | null>(null);
     const [fileUpload, setFileUpload] = useState<FileUpload | null>(null);
+    const fileInputRef = useRef<HTMLInputElement | null>(null);
     const [
         submissionStatus,
         setSubmissionStatus,
@@ -115,6 +116,12 @@ const SubmissionForm: React.FC<SubmissionFormProps> = observer((props) => {
         if (fileUpload) {
             await fileUpload.cancelUpload();
         }
+
+        const input = fileInputRef.current;
+        if (input) {
+            input.value = "";
+        }
+
         setFileUpload(null);
         setSubmissionStatus(null);
         setFormErrors(new FormErrors());
@@ -130,13 +137,32 @@ const SubmissionForm: React.FC<SubmissionFormProps> = observer((props) => {
     const onFileChange = (files: FileList) => {
         const file = files.item(0);
         setFile(file);
+
+        if (file) {
+            validateZip(file).then((result) => {
+                if (result.errors.fileErrors.length > 0) {
+                    setFormErrors(result.errors);
+
+                    if (result.blockUpload) {
+                        result.errors.generalErrors.push(
+                            "An error with your selected file is preventing submission."
+                        );
+                        setSubmissionStatus(SubmissionStatus.ERROR);
+                    }
+                }
+            });
+        }
     };
 
     const onSubmit = async (data: any) => {
         // TODO: Convert to react-hook-form validation
+
+        let fileErrors = formErrors.fileErrors;
         setFormErrors(new FormErrors());
         const errors = new FormErrors();
 
+        errors.fileErrors = fileErrors;
+
         const uploadTeam = data.team ? data.team.value : null;
         const uploadCommunities = data.communities
             ? data.communities.map((com: any) => com.value)
@@ -245,6 +271,8 @@ const SubmissionForm: React.FC<SubmissionFormProps> = observer((props) => {
         (fileUpload?.uploadErrors ?? []).length > 0 ||
         formErrors.generalErrors.length > 0;
 
+    const hasFileErrors = formErrors.fileErrors.length > 0;
+
     const hasEtagError =
         fileUpload &&
         fileUpload.uploadErrors.some(
@@ -296,9 +324,18 @@ const SubmissionForm: React.FC<SubmissionFormProps> = observer((props) => {
                     title={file ? file.name : "Choose or drag file here"}
                     onChange={onFileChange}
                     readonly={!!file}
+                    fileInputRef={fileInputRef}
                 />
             </div>
-
+            {hasFileErrors && (
+                <div className="mb-0 px-3 py-3 alert alert-info field-errors mt-2">
+                    <ul className="mx-0 my-0 pl-3">
+                        {formErrors.fileErrors.map((e, idx) => (
+                            <li key={`general-${idx}`}>{e}</li>
+                        ))}
+                    </ul>
+                </div>
+            )}
             {currentCommunity != null &&
             teams != null &&
             communities != null ? (
@@ -371,7 +408,11 @@ const SubmissionForm: React.FC<SubmissionFormProps> = observer((props) => {
 
                     <button
                         type={"submit"}
-                        disabled={!file || !!fileUpload}
+                        disabled={
+                            !file ||
+                            !!fileUpload ||
+                            submissionStatus == SubmissionStatus.ERROR
+                        }
                         className="btn btn-primary btn-block"
                     >
                         Submit
diff --git a/builder/src/uploadZipValidation.ts b/builder/src/uploadZipValidation.ts
new file mode 100644
index 000000000..7077b7233
--- /dev/null
+++ b/builder/src/uploadZipValidation.ts
@@ -0,0 +1,197 @@
+import { FormErrors } from "./upload";
+import { BlobReader, ZipReader } from "./vendor/zip-fs-full";
+
+export async function validateZip(
+    file: File
+): Promise<{ errors: FormErrors; blockUpload: boolean }> {
+    let errors = new FormErrors();
+
+    let blockUpload = false;
+
+    if (!file.name.toLowerCase().endsWith(".zip")) {
+        errors.fileErrors.push("The file you selected is not a .zip!");
+        blockUpload = true;
+        return { errors, blockUpload };
+    }
+
+    try {
+        const blobReader = new BlobReader(file);
+        const zipReader = new ZipReader(blobReader);
+
+        const entries = await zipReader.getEntries();
+
+        let dllCount = 0;
+        let hasBepInEx = false;
+        let hasAssemblyCSharp = false;
+        let maybeModpack = false;
+        let rootManifest = false;
+        let hasIcon = false;
+        let rootIcon = false;
+        let hasManifest = false;
+        let hasReadMe = false;
+        let rootReadMe = false;
+        let wrongCase = false;
+        let wrongExtension = false;
+        let noExtension = false;
+        for (const entry of entries) {
+            console.log(entry.filename);
+            if (!entry || !(typeof entry.getData === "function")) {
+                continue;
+            }
+
+            if (entry.filename.toLowerCase().endsWith(".dll")) {
+                dllCount++;
+            }
+
+            if (
+                entry.filename.toLowerCase().split("/").pop() ==
+                "assembly-csharp.dll"
+            ) {
+                hasAssemblyCSharp = true;
+            }
+
+            if (
+                entry.filename.toLowerCase().split("/").pop() == "bepinex.dll"
+            ) {
+                hasBepInEx = true;
+                maybeModpack = true;
+            }
+
+            if (entry.filename.toLowerCase().endsWith("manifest.json")) {
+                hasManifest = true;
+                if (entry.filename == "manifest.json") {
+                    rootManifest = true;
+                } else if (entry.filename.toLowerCase() == "manifest.json") {
+                    wrongCase = true;
+                    rootManifest = true;
+                }
+            }
+            if (entry.filename.toLowerCase().endsWith("icon.png")) {
+                hasIcon = true;
+                if (entry.filename == "icon.png") {
+                    rootIcon = true;
+                } else if (entry.filename.toLowerCase() == "icon.png") {
+                    wrongCase = true;
+                    rootIcon = true;
+                }
+            }
+            if (entry.filename.toLowerCase().endsWith("readme.md")) {
+                hasReadMe = true;
+                if (entry.filename == "README.md") {
+                    rootReadMe = true;
+                } else if (entry.filename.toLowerCase() == "readme.md") {
+                    wrongCase = true;
+                    rootReadMe = true;
+                }
+            }
+
+            if (
+                entry.filename.toLowerCase() == "readme.txt" ||
+                entry.filename.toLowerCase() == "manifest.txt" ||
+                entry.filename.toLowerCase() == "icon.jpg" ||
+                entry.filename.toLowerCase() == "icon.jpeg"
+            ) {
+                wrongExtension = true;
+            }
+
+            if (
+                entry.filename.toLowerCase() == "readme" ||
+                entry.filename.toLowerCase() == "manifest" ||
+                entry.filename.toLowerCase() == "icon"
+            ) {
+                noExtension = true;
+            }
+        }
+
+        if (hasBepInEx) {
+            errors.fileErrors.push(
+                "You have BepInEx.dll in your .zip file. BepInEx should probably be a dependency in your manifest.json file instead."
+            );
+        }
+
+        if (hasAssemblyCSharp) {
+            errors.fileErrors.push(
+                "You have Assembly-CSharp.dll in your .zip file. Your package may be removed if you do not have permission to distribute this file."
+            );
+        }
+
+        if (dllCount > 8) {
+            errors.fileErrors.push(
+                "You have " +
+                    dllCount +
+                    " .dll files in your .zip file. Some of these files may be unnecessary."
+            );
+            maybeModpack = true;
+        }
+
+        if (maybeModpack) {
+            errors.fileErrors.push(
+                "If you're making a modpack, do not include the files for each mod in your .zip file. Instead, put the dependency string for each mod inside your manifest.json file."
+            );
+        }
+
+        if (wrongCase) {
+            blockUpload = true;
+            errors.fileErrors.push(
+                "The file names of manifest.json, icon.png, and README.md are case-sensitive."
+            );
+        }
+
+        if (wrongExtension) {
+            blockUpload = true;
+            errors.fileErrors.push(
+                "Your manifest.json, icon.png, and README.md files must have the correct file extensions."
+            );
+        }
+
+        if (
+            hasManifest &&
+            hasIcon &&
+            hasReadMe &&
+            !rootManifest &&
+            !rootIcon &&
+            !rootReadMe
+        ) {
+            blockUpload = true;
+            errors.fileErrors.push(
+                "Your manifest, icon, and README files should be at the root of the .zip file. You can prevent this by compressing the contents of a folder, rather than the folder itself."
+            );
+        } else {
+            if ((!hasManifest || !hasIcon || !hasReadMe) && noExtension) {
+                blockUpload = true;
+                errors.fileErrors.push(
+                    "Your manifest.json, icon.png, or README.md file is missing its file extension."
+                );
+            }
+
+            if (!hasManifest) {
+                blockUpload = true;
+                errors.fileErrors.push(
+                    "Your package is missing a manifest.json file!"
+                );
+            }
+
+            if (!hasIcon) {
+                blockUpload = true;
+                errors.fileErrors.push(
+                    "Your package is missing an icon.png file!"
+                );
+            }
+
+            if (!hasReadMe) {
+                blockUpload = true;
+                errors.fileErrors.push(
+                    "Your package is missing a README.md file!"
+                );
+            }
+        }
+
+        await zipReader.close();
+    } catch (e) {
+        blockUpload = true;
+        errors = new FormErrors();
+        errors.fileErrors.push("Your .zip file could not be read.");
+    }
+
+    return { errors, blockUpload };
+}
diff --git a/builder/src/vendor/zip-fs-full.d.ts b/builder/src/vendor/zip-fs-full.d.ts
index e04aef021..dbda65056 100644
--- a/builder/src/vendor/zip-fs-full.d.ts
+++ b/builder/src/vendor/zip-fs-full.d.ts
@@ -5,122 +5,121 @@
 
 interface FileEntry {}
 
-declare module zip {
-    export var useWebWorkers: boolean;
-    export var workerScriptsPath: string;
-    export var workerScripts: {
-        deflater?: string[] | undefined;
-        inflater?: string[] | undefined;
-    };
-
-    export class Reader {
-        public size: number;
-        public init(callback: () => void, onerror: (error: any) => void): void;
-        public readUint8Array(
-            index: number,
-            length: number,
-            callback: (result: Uint8Array) => void,
-            onerror?: (error: any) => void
-        ): void;
-    }
-
-    export class TextReader extends Reader {
-        constructor(text: string);
-    }
-
-    export class BlobReader extends Reader {
-        constructor(blob: Blob);
-    }
-
-    export class Data64URIReader extends Reader {
-        constructor(dataURI: string);
-    }
-
-    export class HttpReader extends Reader {
-        constructor(url: string);
-    }
-
-    export function createReader(
-        reader: zip.Reader,
-        callback: (zipReader: ZipReader) => void,
+export var useWebWorkers: boolean;
+export var workerScriptsPath: string;
+export var workerScripts: {
+    deflater?: string[] | undefined;
+    inflater?: string[] | undefined;
+};
+
+export class Reader {
+    public size: number;
+    public init(callback: () => void, onerror: (error: any) => void): void;
+    public readUint8Array(
+        index: number,
+        length: number,
+        callback: (result: Uint8Array) => void,
         onerror?: (error: any) => void
     ): void;
+}
+
+export class TextReader extends Reader {
+    constructor(text: string);
+}
+
+export class BlobReader extends Reader {
+    constructor(blob: Blob);
+}
+
+export class Data64URIReader extends Reader {
+    constructor(dataURI: string);
+}
 
-    export class ZipReader {
-        async getEntries(options: any): Promise<Entry[]>;
-        close(callback?: () => void): void;
-    }
-
-    export interface Entry {
-        filename: string;
-        directory: boolean;
-        compressedSize: number;
-        uncompressedSize: number;
-        lastModDate: Date;
-        lastModDateRaw: number;
-        comment: string;
-        crc32: number;
-
-        getData(
-            writer: zip.Writer,
-            onend: (result: any) => void,
-            onprogress?: (progress: number, total: number) => void,
-            checkCrc32?: boolean
-        ): void;
-    }
-
-    export class Writer {
-        public init(callback: () => void, onerror?: (error: any) => void): void;
-        public writeUint8Array(
-            array: Uint8Array,
-            callback: () => void,
-            onerror?: (error: any) => void
-        ): void;
-        public getData(
-            callback: (data: any) => void,
-            onerror?: (error: any) => void
-        ): void;
-    }
-
-    export class TextWriter extends Writer {
-        constructor(encoding: string);
-    }
-
-    export class BlobWriter extends Writer {
-        constructor(contentType: string);
-    }
-
-    export class FileWriter extends Writer {
-        constructor(fileEntry: FileEntry);
-    }
-
-    export class Data64URIWriter extends Writer {
-        constructor(mimeString?: string);
-    }
-
-    export function createWriter(
+export class HttpReader extends Reader {
+    constructor(url: string);
+}
+
+export function createReader(
+    reader: zip.Reader,
+    callback: (zipReader: ZipReader) => void,
+    onerror?: (error: any) => void
+): void;
+
+export class ZipReader {
+    constructor(reader: BlobReader);
+    async getEntries(options?: any): Promise<Entry[]>;
+    close(callback?: () => void): void;
+}
+
+export interface Entry {
+    filename: string;
+    directory: boolean;
+    compressedSize: number;
+    uncompressedSize: number;
+    lastModDate: Date;
+    lastModDateRaw: number;
+    comment: string;
+    crc32: number;
+
+    getData(
         writer: zip.Writer,
-        callback: (zipWriter: zip.ZipWriter) => void,
-        onerror?: (error: any) => void,
-        dontDeflate?: boolean
+        onend: (result: any) => void,
+        onprogress?: (progress: number, total: number) => void,
+        checkCrc32?: boolean
+    ): void;
+}
+
+export class Writer {
+    public init(callback: () => void, onerror?: (error: any) => void): void;
+    public writeUint8Array(
+        array: Uint8Array,
+        callback: () => void,
+        onerror?: (error: any) => void
+    ): void;
+    public getData(
+        callback: (data: any) => void,
+        onerror?: (error: any) => void
     ): void;
+}
+
+export class TextWriter extends Writer {
+    constructor(encoding: string);
+}
+
+export class BlobWriter extends Writer {
+    constructor(contentType: string);
+}
 
-    export interface WriteOptions {
-        directory?: boolean | undefined;
-        level?: number | undefined;
-        comment?: string | undefined;
-        lastModDate?: Date | undefined;
-        version?: number | undefined;
-    }
-
-    export class ZipWriter {
-        public add(
-            name: string,
-            reader: zip.Reader,
-            onend: () => void,
-            onprogress?: (progress: number, total: number) => void,
-            options?: WriteOptions
-        ): void;
-        public close(callback: (result: any) => void): void;
-    }
+export class FileWriter extends Writer {
+    constructor(fileEntry: FileEntry);
+}
+
+export class Data64URIWriter extends Writer {
+    constructor(mimeString?: string);
+}
+
+export function createWriter(
+    writer: zip.Writer,
+    callback: (zipWriter: zip.ZipWriter) => void,
+    onerror?: (error: any) => void,
+    dontDeflate?: boolean
+): void;
+
+export interface WriteOptions {
+    directory?: boolean | undefined;
+    level?: number | undefined;
+    comment?: string | undefined;
+    lastModDate?: Date | undefined;
+    version?: number | undefined;
+}
+
+export class ZipWriter {
+    public add(
+        name: string,
+        reader: zip.Reader,
+        onend: () => void,
+        onprogress?: (progress: number, total: number) => void,
+        options?: WriteOptions
+    ): void;
+    public close(callback: (result: any) => void): void;
 }