# SLCL Mobile App vs Constraint Engine

The clearest difference is in-app purchases: SLCL Mobile App at none against Constraint Engine's 2. Constraint Engine's advantage is update cadence (daily vs every 2 months). On price, ads, device support and iOS requirement there is nothing between them.

Both are free to download. Constraint Engine sells 2 in-app purchases, starting at $4.99 per month. SLCL Mobile App asks for nothing beyond the download.

SLCL Mobile App ships an update every 2 months, Constraint Engine daily. The most recent releases landed on October 20, 2026 and October 5, 2026 respectively.

## The numbers

| Metric | SLCL Mobile App | Constraint Engine |
| --- | --- | --- |
| Price | Free | Free |
| Rating | **[2.5 (44 ratings)](https://appshunter.io/ios/app/slcl-mobile-app/id1184084004/reviews)** | — |
| Number of ratings | **44** | — |
| Positive reviews | 27.9% of reviews | — |
| In-app purchases | **No** | Yes |
| Ads | No | No |
| Update frequency | Every 2 months | **Daily** |
| Monetization | Free | — |
| Size | 50 MB | 10 MB |
| Requires iOS | **15.6** | 16.0 |
| Devices | **iPhone, iPad, iPod** | iPhone, iPad |
| Age rating | 17+ | 4+ |
| Developer | [St. Louis County Library District](https://appshunter.io/developer/493866179) | [Mark Barker](https://appshunter.io/developer/1896741919) |

## What reviewers say

### SLCL Mobile App

[App page](https://appshunter.io/ios/app/slcl-mobile-app/id1184084004)

Access your library account 24/7 from anywhere. Manage loans, search the catalog, request materials, and download eMedia. Find branches, view events, and get help from librarians.

**Highlights:** Manage library account, Search catalog, Renew and request materials, Download eMedia, View events and classes, Locate branches, Ask a Librarian support

**Features:** macOS Compatibility, Vision Pro support

**In-app purchases:** none

**What reviewers like**

- 👍 Simple and functional for basic use
- 📱 Self-checkout barcode on phone
- 🌟 Librarian chat is amazing
- ✨ New look is user-friendly
- 🗓️ Events and classes feature is convenient

**What reviewers complain about**

- 🐛 No notifications for holds
- 📱 Pickup date phrase too long for mobile
- 🐛 Barcode scanning doesn't work
- 💡 Missing 'Save for Later' list sync with website
- 💡 No way to view or add to lists in app

**Reported bugs**

- No notifications for holds
- Barcode scanning fails
- Pickup date phrase too long for mobile screens
- Chat history lost on app close
- Search results inconsistent with website

**Requested features**

- Make pickup date phrase shorter for mobile
- Sync 'Save for Later' list with website
- Allow viewing and adding to lists in app
- More search filters for books and media
- Recommendations based on checkout history


### Constraint Engine

[App page](https://appshunter.io/ios/app/constraint-engine/id6772520332)

**In-app purchases (2)**

| Purchase | Price | Billing |
| --- | --- | --- |
| Constraint Engine Pro | $4.99 | per month |
| Constraint Engine Pro | $29.99 | per year |


## Frequently asked questions

### Is SLCL Mobile App free?

SLCL Mobile App is free to download, with no in-app purchases.

### Is Constraint Engine free?

Constraint Engine is free to download, with in-app purchases available.

### Do SLCL Mobile App or Constraint Engine have ads?

Neither SLCL Mobile App nor Constraint Engine shows ads.

### Which is updated more often, SLCL Mobile App or Constraint Engine?

SLCL Mobile App ships an update every 2 months, and Constraint Engine daily. Most recently, SLCL Mobile App was updated on October 20, 2026 and Constraint Engine on October 5, 2026.

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*Compared by [AppsHunter](https://appshunter.io/) from daily US App Store data. Review summaries are generated from verbatim App Store reviews.*