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Embedded Trial Keys in .NET: Ship Evaluation Versions Without a Server

#dotnet #csharp #trial #licensing

You want to ship a trial version of your app. Here's the easiest way: embed a trial key directly in the code.

No server. No activation. Just works.

Why Embedded Trial Keys?

Traditional trial approach:

  1. User downloads app
  2. User registers on your website
  3. You email a trial key
  4. User enters key in app
  5. App validates online

Result: 30-40% of users drop off before trying your app.

Embedded trial approach:

  1. User downloads app
  2. App runs immediately (trial key embedded)
  3. User evaluates

Result: 100% trial start rate.

Step 1: Create a Trial Key

In QLM Management Console:

1. Manage Keys → Create
2. Product: [Your Product]
3. License Model: Trial
4. Expiry Date: 30 days from today
5. Number of Licenses: 1
6. Click OK
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Copy the generated key (example: A5B3C-D8E2F-G1H4I-J7K9L-M3N6P).

Step 2: Embed the Key 

using System;
using QLM.LicenseLib;

class Program
{
    // Embedded trial key - same for all users
    private const string TRIAL_KEY = "A5B3C-D8E2F-G1H4I-J7K9L-M3N6P";

    static void Main(string[] args)
    {
        if (ValidateLicense())
        {
            Console.WriteLine("Trial active - running app");
            RunApp();
        }
        else
        {
            Console.WriteLine("Trial expired or invalid");
        }
    }

    static bool ValidateLicense()
    {
        var lv = new LicenseValidator("settings.xml");

        bool needsActivation = false;
        string errorMsg = string.Empty;

        // First check if license exists locally
        bool isValid = lv.ValidateLicenseAtStartup(
            ELicenseBinding.ComputerName,
            ref needsActivation,
            ref errorMsg
        );

        // If no license found, use embedded trial key
        if (!isValid && string.IsNullOrEmpty(lv.ActivationKey))
        {
            lv.ActivationKey = TRIAL_KEY;
            lv.ComputerKey = string.Empty;

            isValid = lv.ValidateLicenseAtStartup(
                ELicenseBinding.ComputerName,
                ref needsActivation,
                ref errorMsg
            );

            if (isValid)
            {
                // Store trial key locally for next run
                lv.QlmLicenseObject.StoreKeys(lv.ActivationKey, lv.ComputerKey);
                Console.WriteLine("Trial started - 30 days remaining");
            }
        }

        return isValid;
    }

    static void RunApp()
    {
        // Your application code here
    }
}
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How It Works

  1. First run: App checks for local license → none found
  2. App uses embedded key: Validates it against expiry date
  3. Trial starts: Key stored locally, expiry date locked
  4. Subsequent runs: App uses stored license
  5. After 30 days: License expires, app stops working

Important: The trial period starts on first use, not when you create the key. The expiry date is calculated from first validation.

Upgrade Path

When the user purchases, they get a permanent key:

// User enters purchased key via QLM License Wizard
// Wizard replaces trial key with permanent key
// App validates and works indefinitely
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Show Days Remaining 

static void ShowTrialStatus(LicenseValidator lv)
{
    if (lv.QlmLicenseObject.LicenseModel == ELicenseModel.trial)
    {
        DateTime expiryDate = lv.QlmLicenseObject.ExpiryDate;
        int daysLeft = (expiryDate - DateTime.Now).Days;

        if (daysLeft > 0)
        {
            Console.WriteLine($"Trial: {daysLeft} days remaining");
        }
        else
        {
            Console.WriteLine("Trial expired");
        }
    }
}
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Alternative: Different Key Per User

If you want to track each download:

// Generate trial key server-side when user downloads
// Embed unique key per user
// Track which keys are activated
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But this requires a server call. The embedded approach is simpler.

Pros & Cons

Pros:

  • ✅ Zero friction — app runs immediately
  • ✅ No server required for trial
  • ✅ Works offline
  • ✅ Same binary for trial & paid

Cons:

  • ❌ Can't track who tries your app
  • ❌ Key can be extracted (not a real issue for trials)
  • ❌ One key for all users (acceptable for trials)

When to Use This

Use embedded keys when:

  • Frictionless trial is priority #1
  • You don't need to track trial users
  • You want offline trial support

Don't use when:

  • You need to track every download
  • You want unique keys per user
  • You need trial usage analytics

Supported Platforms

  • Windows: .NET Framework 2.x / 4.x, .NET 6/7/8/9/10
  • Cross-platform: .NET 6/7/8/9/10 (macOS, Linux)
  • Mobile: Android, iOS (.NET MAUI, Xamarin)

Quick License Manager

This uses Quick License Manager (QLM).

Pricing (per developer):

  • QLM Express: $200/year
  • QLM Professional: $699/year
  • QLM Enterprise: $999/year

Download 30-day trial

Resources

Related articles:

How do you handle trials in your apps? Share in the comments! 👇

Quick License Manager by Soraco Technologies — https://soraco.co

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