📚 Mendeley Scholar Checker

A Chrome extension that checks Google Scholar search results against your personal Mendeley library in real time — and lets you add papers with a single click.

---

✨ Features

Badge	Meaning	Action
✅ In Mendeley (green)	Paper already in your library	—
➕ Add to Mendeley (blue)	Not in library	Click to add instantly
➕ Add to Mendeley + PDF (blue)	Free PDF detected	Click to add with PDF
⏳ Checking… (gray, pulsing)	Querying your library	Wait
⚠️ Login required (amber)	Not connected	Click extension icon

• Matches by DOI first (exact), then fuzzy title match as fallback
• Auto-saves title, authors, year, journal, and URL to Mendeley when adding
• Tries to attach a free PDF automatically via Unpaywall and open-access sources
• Validates downloaded files are real PDFs before attaching (no corrupt files)
• Works on Google Scholar search results pages
• Handles dynamic pagination — badges appear on newly loaded results too

---

🗂 Project Structure

mendeley-scholar-checker/
├── background.js       # OAuth2 + Mendeley API logic (source — no real secrets)
├── content.js          # Scrapes Scholar, injects badges, handles click-to-add
├── popup.html          # Extension popup UI (login/logout)
├── popup.js            # Popup logic
├── styles.css          # Badge styles injected into Scholar pages
├── manifest.json       # Chrome Extension Manifest V3 config
├── build.js            # Build script: reads .env → generates dist/
├── get_key.py          # Helper: converts Extension ID → manifest key
├── package.json        # npm scripts
├── .env.example        # Template — copy to .env and fill in credentials
├── .gitignore          # Keeps .env and dist/ out of GitHub
├── icons/              # Extension icons (16px, 48px, 128px)
└── dist/               # ← Generated by build.js (gitignored, load THIS in Chrome)

Important: Always load the dist/ folder in Chrome, not the root folder. The dist/ folder contains your credentials injected by the build script.

---

🚀 Quick Start

What you need

• Google Chrome
• Node.js v14+ — download and install from nodejs.org (just click Next through the installer)
• A Mendeley / Elsevier account — register free at mendeley.com
• Any text editor — Notepad on Windows, TextEdit on Mac, nano in terminal, anything works

No VS Code, no Git, no other tools required.

---

Step 1 — Get the code

Click the green Code button on this GitHub page → Download ZIP → unzip the folder anywhere you like.

Open a terminal inside the unzipped folder:

• Windows: open the folder → click the address bar → type cmd → press Enter
• Mac: right-click the folder → "New Terminal at Folder"
• Linux: right-click → "Open Terminal Here"

---

Step 2 — Do an initial build

In the terminal, run:

node build.js

It will warn about missing credentials — that's fine for now. The dist/ folder will still be created.

---

Step 3 — Load the extension in Chrome

1. Open Chrome and go to chrome://extensions/

2. Toggle Developer mode ON (switch in the top-right corner)

3. Click Load unpacked → select the dist/ folder inside the project

4. Find Mendeley Scholar Checker in the list

5. Copy the ID shown below the name (only visible when Developer mode is ON):

   ID: abcdefghijklmnopqrstuvwxyzabcdef
   

---

Step 4 — Pin your Extension ID (important!)

Without this step, Chrome assigns a new Extension ID every time you remove and re-add the extension, which breaks the login. Run this once to lock it permanently:

python3 get_key.py abcdefghijklmnopqrstuvwxyzabcdef

Replace the ID with your actual ID from Step 3. On Windows you may need to use python instead of python3.

The output will look like:

✅  Extension ID : abcdefghijklmnopqrstuvwxyzabcdef
🔑  Key          : AAAAAABBBBBBCCCCCC...
🔗  Redirect URL : https://abcdefghijklmnopqrstuvwxyzabcdef.chromiumapp.org/

Copy both the Key and the Redirect URL — you need them in the next two steps.

---

Step 5 — Register a Mendeley API app

1. Go to dev.mendeley.com/myapps.html

2. Sign in with your Elsevier credentials (same email/password as Mendeley)

3. Click Create new app and fill in the form:

   Field	Value
   App Name	Scholar Checker (or anything you like)
   Description	Personal Chrome extension to check Mendeley library
   Authorisation Flow	Elsevier
   Redirect URL	Paste your https://...chromiumapp.org/ from Step 4

4. Click Register → copy the Client ID and Client Secret shown

⚠️ Do not click "Pack extension" on chrome://extensions/ — that's unrelated and not needed here.

---

Step 6 — Configure your credentials

Copy the example credentials file:

# Mac / Linux
cp .env.example .env

# Windows (Command Prompt)
copy .env.example .env

# Windows (PowerShell)
Copy-Item .env.example .env

Open .env with any text editor and fill in all three values:

MENDELEY_CLIENT_ID=paste_your_client_id_here
MENDELEY_CLIENT_SECRET=paste_your_client_secret_here
EXTENSION_KEY=paste_your_key_here

⚠️ Never share this file or commit it to GitHub — it's already in .gitignore so it's protected automatically.

---

Step 7 — Build and reload

node build.js

Then go to chrome://extensions/ → find Mendeley Scholar Checker → click ↻ Reload.

---

Step 8 — Connect your Mendeley account

1. Click the extension icon in the Chrome toolbar (puzzle piece icon → pin it for easy access)
2. Click Connect Mendeley
3. An Elsevier login window appears — sign in with your Mendeley credentials
4. The popup shows Connected to Mendeley ✅

---

Step 9 — Use it!

Go to scholar.google.com, search for any topic, and badges will appear on each result within a few seconds.

• Blue badge → click to save the paper (+ PDF if one is freely available)
• Green badge → already in your library

---

🔄 After Making Changes

If you edit any source file, rebuild and reload:

node build.js

Then chrome://extensions/ → ↻ Reload.

---

🔒 Security Notes

File	Goes to GitHub?	Why
.env	❌ No	Contains your real secrets
dist/	❌ No	Contains injected secrets
.env.example	✅ Yes	Placeholder values only
background.js	✅ Yes	Placeholder values only
manifest.json	✅ Yes	Placeholder values only

---

🐛 Troubleshooting

"Login error: Authorization page could not be loaded"

• Your Extension ID changed — run python3 get_key.py <new-id>, update EXTENSION_KEY in .env, run node build.js, reload, and update the Redirect URL in your Mendeley app settings

"Login error: Token exchange failed: 403"

• The Redirect URL in Mendeley app settings doesn't match your Extension ID
• Go to dev.mendeley.com/myapps.html → edit your app → update the Redirect URL

"Login required" badge on every result

• Click the extension icon → reconnect (token expired)

No badges appearing

• Make sure you're on a Google Scholar search results page (URL contains scholar.google.com/scholar?)
• Confirm the popup says "Connected to Mendeley"
• Try reloading the Scholar page

"Add failed" on a paper

• Open chrome://extensions/ → click Service worker → Console tab → retry adding → paste the error here

PDF not attached

• Expected for paywalled papers (IEEE, Elsevier, Springer). The extension only attaches PDFs from free/open-access sources. The paper metadata is always saved regardless.

---

📄 License

MIT — free to use, modify, and share.