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.NET, .NET Core

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Getting started:

1. Install ConfigCat SDK Nuget package

Install-Package ConfigCat.Client

2. Import package

using ConfigCat.Client

3. Create the ConfigCat client with your SDK Key

var client = new ConfigCatClient("#YOUR-SDK-KEY#");

4. Get your setting value

var isMyAwesomeFeatureEnabled = client.GetValue("isMyAwesomeFeatureEnabled", false);

5. Dispose ConfigCat client

You can safely dispose() the client instance and release all associated resources on application exit.


Creating the ConfigCat Client

ConfigCat Client is responsible for:

  • managing the communication between your application and ConfigCat servers.
  • caching your setting values and feature flags.
  • serving values quickly in a failsafe way.

new ConfigCatClient() creates a client with default options.

SdkKeyREQUIRED. SDK Key to access your feature flags and configurations. Get it from ConfigCat Dashboard.
ConfigCacheIConfigCache instance for cache the config.InMemoryConfigCache
LoggerILogger instance for tracing.ConsoleLogger (with WARNING level)
HttpClientHandlerHttpClientHandler to provide network credentials and proxy settingsbuilt-in HttpClientHandler
DataGovernanceDescribes the location of your feature flag and setting data within the ConfigCat CDN. This parameter needs to be in sync with your Data Governance preferences. More about Data Governance. Available options: Global, EuOnlyGlobal

AutoPollConfiguration, LazyLoadConfiguration, ManualPollConfiguration
Creating the client is different for each polling mode. See below for details.


We strongly recommend you to use the ConfigCatClient as a Singleton object in your application. If you want to use multiple SDK Keys in the same application, create only one ConfigCatClient per SDK Key.

Anatomy of GetValue(), GetValueAsync()

keyREQUIRED. Setting-specific key. Set on ConfigCat Dashboard for each setting.
defaultValueREQUIRED. This value will be returned in case of an error.
userOptional, User Object. Essential when using Targeting. Read more about Targeting.
User userObject = new User("435170f4-8a8b-4b67-a723-505ac7cdea92");
client.GetValue("keyOfMySetting", false, userObject);

User Object

The User Object is essential if you'd like to use ConfigCat's Targeting feature.

User userObject = new User("435170f4-8a8b-4b67-a723-505ac7cdea92");
User userObject = new User("[email protected]");
IdREQUIRED. Unique identifier of a user in your application. Can be any string value, even an email address.
EmailOptional parameter for easier targeting rule definitions.
CountryOptional parameter for easier targeting rule definitions.
CustomOptional dictionary for custom attributes of a user for advanced targeting rule definitions. e.g. User role, Subscription type.
User userObject = new User("435170f4-8a8b-4b67-a723-505ac7cdea92") {
Email = "[email protected]",
Country = "United Kingdom",
Custom = new Dictionary<string, string> {
{"SubscriptionType", "Pro"},
{"UserRole", "Admin"}}

Polling Modes

The ConfigCat SDK supports 3 different polling mechanisms to acquire the setting values from ConfigCat. After latest setting values are downloaded, they are stored in the internal cache then all GetValue() calls are served from there. With the following polling modes, you can customize the SDK to best fit to your application's lifecycle.

Auto polling (default)

The ConfigCat SDK downloads and stores the latest values automatically every 60 seconds.

Use the PollIntervalSeconds option parameter to change the polling interval.

var clientConfiguration = new AutoPollConfiguration
SdkKey = "#YOUR-SDK-KEY#",
PollIntervalSeconds = 95
IConfigCatClient client = new ConfigCatClient(clientConfiguration);

Subscribing to the OnConfigurationChanged event will get you notified about changes.

var clientConfiguration = new AutoPollConfiguration
SdkKey = "#YOUR-SDK-KEY#"
clientConfiguration.OnConfigurationChanged += (sender, args) =>
Console.WriteLine("Your config has been changed!");
IConfigCatClient client = new ConfigCatClient(clientConfiguration);

Available options:

Option ParameterDescriptionDefault
PollIntervalSecondsPolling interval.60
MaxInitWaitTimeSeconds Maximum waiting time between the client initialization and the first config acquisition in seconds.5

Lazy loading

When calling GetValue() or GetValueAsync() the ConfigCat SDK downloads the latest setting values if they are not present or expired in the cache. In this case the GetValue()) or GetValueAsync() will return the setting value after the cache is updated.

Use CacheTimeToLiveSeconds parameter to manage configuration lifetime.

var clientConfiguration = new LazyLoadConfiguration
SdkKey = "#YOUR-SDK-KEY#",
CacheTimeToLiveSeconds = 600
IConfigCatClient client = new ConfigCatClient(clientConfiguration);

Available options:

Option ParameterDescriptionDefault
CacheTimeToLiveSecondsCache TTL.60

Manual polling

Manual polling gives you full control over when the config.json (with the setting values) is downloaded. ConfigCat SDK will not update them automatically. Calling ForceRefresh() is your application's responsibility.

var clientConfiguration = new ManualPollConfiguration
SdkKey = "#YOUR-SDK-KEY#"
IConfigCatClient client = new ConfigCatClient(clientConfiguration);


GetValue() returns defaultValue if the cache is empty. Call ForceRefresh() to update the cache.

var clientConfiguration = new ManualPollConfiguration
SdkKey = "#YOUR-SDK-KEY#"
IConfigCatClient client = new ConfigCatClient(clientConfiguration);

Console.WriteLine(client.GetValue("key", "my default value")); // console: "my default value" client.ForceRefresh(); Console.WriteLine(client.GetValue("key", "my default value")); // console: "value from server"

## Logging
### Setting log levels
var client = new ConfigCatClient("#YOUR-SDK-KEY#");

client.LogLevel = LogLevel.Info;

Available log levels:

OffNothing is logged.
ErrorOnly error level events are logged.
WarningErrors and Warnings are logged.
InfoErrors, Warnings and feature flag evaluation is logged.
DebugAll of the above plus debug info is logged.

Info level logging helps to inspect the feature flag evaluation process:

ConfigCat - Info -  Evaluate 'isPOCFeatureEnabled'
User object: {"Identifier":"<SOME USERID>","Email":"[email protected]","Country":"US","Custom":{"SubscriptionType":"Pro","Role":"Admin","version":"1.0.0"}}
evaluate rule: '[email protected]' CONTAINS '' => no match
evaluate rule: '[email protected]' CONTAINS '' => match
Returning: True

Sample code on how to create a basic file logger implementation for ConfigCat client: See Sample Code

Configuration with ConfigCatClientBuilder

You can use ConfigCatClientBuilder to create the ConfigCat client instance:

IConfigCatClient client = ConfigCatClientBuilder


You can get all the setting keys from your configuration by calling the GetAllKeys() method of the ConfigCatClient.

IConfigCatClient client = new ConfigCatClient("#YOUR-SDK-KEY#");
IEnumerable<string> keys = client.GetAllKeys();

Using ConfigCat behind a proxy

Provide your own network credentials (username/password), and proxy server settings (proxy server/port) by injecting a HttpClientHandler instance into the ConfigCatClient's configuration.

var myProxySettings = new WebProxy(proxyHost, proxyPort)
UseDefaultCredentials = false,
Credentials = new NetworkCredential(proxyUserName, proxyPassword)

var myHttpClientHandler = new HttpClientHandler { Proxy = myProxySettings };

var client = new ConfigCatClient(new AutoPollConfiguration
HttpClientHandler = myHttpClientHandler,
SdkKey = "#YOUR-SDK-KEY#",

Sample Applications

Check out our Sample Applications how they use the ConfigCat SDK:

Look under the hood