Tiny runtime JSON config manager for fetching, caching and resolving application settings with conditional overrides, scheduled activation, string/semver matching and a client for automated retrieval.
This is a tiny library to manage run-time arbitrary config stored as json on a server.
The json format should look like this
{
"settings": {},
"overrides": {}
}
The settings key holds the app configuration for your application. This is an
arbitrary json object specific to your app.
The optional overrides key holds any override based on runtime properties you provide to the
library.
The example below shows a more complete example that as an override that is active
when the platform is ios and the current date is between the first of January and
the 10th of January 2026.
While both from and to are specified for the schedule property in this example,
only from or to is required. The schedule property itself is optional.
With in the time the override is active the effective config will be
{
"greeting": "Happy new year dear iOS user!",
"should_greet": true
}
A config class is a data class with default values that is @Serializable with Kotlin
serialization.
@Serializable
data class MyConfig(
val greeting: String = "Hello world",
@SerialName("should_greet") val shouldGreet: Boolean = false
)
To resolve the configuration, it should first be deserialized into the Config
data class provided by the library. The
Config
data class represents the settings
with their overrides as stored on the server.
val config: Config = fetchConfigAndDeserialize()
val myConfig: MyConfig = config.resolve(
MyConfig.serializer(),
propertiesOf(
// the property is set based on runtime conditions
"platform" to StringProperty("android"),
// other properties that are used for overrides
)
)
println(myConfig) // prints MyConfig(greeting=Hello world, shouldGreet=true)
A RuntimeProperty is a property that is defined to match
overrides in a setting. Each override has a matching property with a map of keys and
values. For an override to apply all properties in a single override should match.
Two implementations for RuntimeProperty are provided, a StringProperty that
matches values and a VersionProperty that uses
the semver
library to match versions and version ranges.
To fetch, cache and resolve config the client module provides MicroConfigClient.
This work was inspired on https://github.com/egeniq/app-remote-config
/*
* Copyright 2025 Little Robots
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
Surfaced from shared tags and platforms — no rankings paid for.
{
"settings": {
"greeting": "Hello from my app",
"should_greet": true
},
"overrides": [
{
"matching": [
{
"platform": "ios"
}
],
"settings": {
"greeting": "Happy new year dear iOS user!"
},
"schedule": {
"from": "2026-01-01T00:00:00Z",
"to": "2026-01-10T00:00:00Z"
}
}
]
}