Parallel Download Manager
IDM-inspired parallel downloading for recognized direct HTTP(S) file links.
Parallel Download Manager is a userscript—not a browser-wide replacement for Chrome’s download system. It shows an in-page choice dialog for recognized direct file links and offers a manual URL option for links that a website does not expose as a standard anchor.
✨ Features
- Parallel segmented downloads — splits range-enabled files into 16 MiB chunks and downloads them with up to 4–8 connections, based on available hardware and segment count.
- Range-response validation — verifies each segment’s
Content-Range, byte length, ETag, and Last-Modified value when those validators are supplied by the server.
- Automatic retry and rate-limit backoff — retries transient failures and reduces concurrency after HTTP 429 responses.
- Two save modes — Chromium’s
showSaveFilePicker() writes directly to disk on HTTPS; other supported contexts use a Blob/memory fallback.
- Manual direct-URL fallback — use the userscript-manager command Parallel Download Manager: Download URL… to paste a direct HTTP(S) file URL when a page link does not show the choice dialog.
- Status diagnostics — use Parallel Download Manager: Status to confirm that the script is active and see why the last click was not intercepted.
- Cancel safely — stops active requests, retry timers, and partial output.
- Live connection progress — displays overall progress plus individual connection lanes.
- Dark IDM-style dialog — a compact in-page interface for selecting and monitoring downloads.
🔧 How to use it
Option 1: Click a recognized direct file link
- Reload the page after installing or updating the script.
- Click a normal, unmodified left-click direct file link.
- In the in-page dialog, choose one of these options:
- Browser download — continues the site’s normal download behavior. Chrome’s built-in download UI is expected in this mode.
- Segmented download — checks byte-range support, downloads the file in segments, validates the responses, and assembles the final file.
Links with a download attribute or common file extension are recognized directly. For extensionless links, the script combines action labels such as Download, Free download, Direct download, and Download 100 MB with download-like URL routes, button metadata, and accessible icon names. Strong labels qualify directly; weaker hints must agree so ordinary navigation is not interrupted.
Option 2: Paste a direct URL manually
If clicking a page download control does not open the dialog:
- Open your userscript manager’s menu.
- Choose Parallel Download Manager: Download URL….
- Paste the final direct
http:// or https:// file URL.
- Select Continue, then choose Browser download or Segmented download.
This option is useful for signed URLs, uncommon extensions, and sites that implement their visible download control as something other than a standard link.
🧪 Test it
For a meaningful segmented-download test, use an HTTPS file larger than 16 MiB served by a range-enabled endpoint that returns 206 Partial Content and a valid Content-Range header.
Expected result:
- The choice dialog appears after clicking the direct link or entering its URL manually.
- Segmented download verifies range support.
- Files larger than 16 MiB show multiple connection lanes.
- The saved file matches the hosted file byte-for-byte.
A local or self-hosted test endpoint is recommended because public test links, redirects, range behavior, and rate limits can change without notice.
📋 Requirements
- A current Chromium-based browser such as Chrome, Edge, or Brave is recommended for direct-to-disk saving.
- Tampermonkey or Violentmonkey with the script enabled. Compatibility with other userscript managers should be verified before relying on it.
- Chrome 138+ users must enable Allow User Scripts in the userscript manager extension’s details page.
- The userscript manager needs access to the relevant websites—On all sites is required for automatic detection across sites.
- Reload the page after installation or after changing extension permissions.
- Segmented mode requires that the target server supports HTTP Range requests.
Your userscript manager may ask for permission to request the file host. Allow only hosts you trust.
⚠️ Limitations
- This is not a browser-wide download manager. The script can act only before a supported page-level click or after you provide a direct URL manually.
- Browser download intentionally uses the browser. Chrome’s regular download UI will appear when you select Browser download. Blob fallback saves can also appear in the browser’s download UI after assembly.
- Some page download flows cannot be automatically intercepted. This includes browser/address-bar downloads, forms, generic buttons, JavaScript-generated requests,
blob: and data: URLs, iframe downloads, embedded or streaming media, and downloads that require private application headers or page-specific authentication logic.
- Large files over 512 MiB need direct disk access. Without Chromium’s HTTPS save-file picker, the script must assemble the download in memory and refuses files above 512 MiB. Large in-memory downloads can require substantial additional browser memory.
- Small files may use one connection. Files at or below 16 MiB are retrieved as a single verified range, so parallel lanes are expected only for larger files.
- Range support is mandatory for segmented mode. If the server ignores ranges or returns invalid range headers, use Browser download instead.
🛠️ No dialog appears
- Confirm the script is enabled, then reload the page.
- Confirm Allow User Scripts is enabled in Chrome and the manager has site access for the page.
- Open Parallel Download Manager: Status from the userscript-manager menu to see the last click decision.
- Make sure the item is a direct HTTP(S) link, not a form, media player, or JavaScript-driven button.
- Use Parallel Download Manager: Download URL… with the final direct file URL.
- If the issue remains, include your browser/version, userscript manager/version, page URL, shareable direct URL, and the Status message when reporting it.
🛡️ Privacy
This script does not collect, transmit, or share data. It requests only the URL you click or explicitly paste into the manual dialog.
