A Kotlin Multiplatform engine for text templates, with no third-party production dependencies. JVM (Java 11+), JavaScript/Node.js and Linux x64 Native are tested in CI. Host-specific macOS x64 and Windows x64 targets are configured but are not covered by CI; ARM Native artifacts are not currently configured. Kotlin has deprecated the macOS x64 target.

Use Maven Central and the root multiplatform artifact:

repositories { mavenCentral() }
// In commonMain.dependencies (or dependencies for a JVM project):
implementation("dev.limebeck:ko-te:0.6.0")

The latest release is 0.6.0. Its signed artifacts have been uploaded to Central Portal and published to GitHub Packages. Maven Central availability is pending Portal publication and propagation; the dependency above will resolve once that completes. See CHANGELOG.md for migration notes.

Rendering is suspending. Call it from a coroutine or a suspending function:

import dev.limebeck.templateEngine.KoTeRenderer

suspend fun greeting(): String {
    val renderer = KoTeRenderer()
    return renderer.render(
        "Hello, {{ name }}! Object value: {{ object.value[0] }}",
        mapOf("name" to "World", "object" to mapOf("value" to listOf("example")))
    ).getValueOrNull()!!
}

The result is Hello, World! Object value: example.

Variable: {{ variable }}
Object key: {{ object.value }}
List index (non-negative Int literal): {{ array[0] }}
Host function: {{ uppercase(variable) }}
Assignment: {{ let newVariable = "value" }}
Multiline code: {{
    let first = 20
    let second = 30
    first + second
}}
Conditional: {{ if(value) }}yes{{ else }}no{{ endif }}
Import: {{ import "resourceName" }}

Functions such as uppercase are provided by the host through predefinedObjectsProvider; there is no implicit standard function set. Imports use the supplied ResourceLoader and share the current render's variables. Import cycles and depth greater than 64 are rejected. Each top-level render has its own context and import stack.

Pipe syntax and template inheritance are not implemented.

Conditions emit every node of the selected branch, in source order. Loops emit their body once per item, and imports emit the imported template at the import position. Assignments emit no text. Empty bodies and loops over empty lists produce no output.

{{ for item in items }}[{{ loop.number }}: {{ item }}]{{ endfor }}

For items = listOf("a", "b"), the result is [1: a][2: b]. The iterable must still be a variable containing a list; it is read once before iteration. Each iteration provides loop.index (zero-based), loop.number (one-based), loop.first, loop.last and loop.length. The name loop cannot be used as the item variable.

Nested loops temporarily shadow the outer item and loop metadata. These bindings are restored after the loop, including when evaluation throws or is cancelled. Other assignments retain their existing shared-context behavior, including assignments made by imported templates. Values inside blocks retain their usual formatting: lists and maps are JSON, while the combined block output is plain text. No additional HTML escaping is applied.

Since 0.4.0, blocks render their complete output. In 0.3.0, loops discarded their body output and conditions returned only the last result of the selected branch. This is an intentional compatibility change. See the block specification for examples and compatibility details.

From highest to lowest precedence: calls/field/index access, unary + - !, * / %, binary + -, ==. Binary operators are left-associative; prefixes nest right-to-left. Parentheses override precedence, including in function arguments. Division of integral values truncates toward zero. Unary + and - require numbers; ! requires a Boolean. Unary operators are available since 0.6.0. See unary operators for examples and numeric boundaries.

Numeric operations use checked Long arithmetic for integral values in the Long range and Double arithmetic for fractional values. This includes integral-valued Float/Double input (e.g. 5.0 / 2.0 is 2), giving the same behavior on JS, where numeric JVM types are not preserved. Fractional literals are parsed as Double. Overflow, division by zero and non-finite results throw KoteRuntimeException. Mixing integers outside ±9,007,199,254,740,991 with fractional values is rejected to avoid silent conversion loss. Float/Double inputs already have their host language's floating-point precision; the engine cannot restore lost digits.

Data can contain strings, booleans, supported numeric values, lists, string-keyed maps, RuntimeObject values and null. Nulls retain their list positions; top-level null is accepted. Null renders as null. Since 0.5.0, the null literal works in expressions, assignments and function arguments. null == null is true; null does not equal a string, number or Boolean.

Access is strict: absent variables, missing object fields and out-of-range list indices throw KoteRuntimeException. An explicit null field or list element remains a value. Accessing a field/index of null also fails; null is not implicitly converted to Boolean or another type. Supply optional fields as null in the input data, then guard their use with if (value == null). See null and missing-value semantics for migration from 0.4.0.

Single- and double-quoted strings support \\, \", \', \/, \n, \r, \t, \b, \f and \uXXXX. Triple-double-quoted strings are raw and can span multiple lines. Template delimiters inside strings are literal text. Invalid or unterminated strings are errors.

Strings are emitted as plain text. Maps and lists are emitted as JSON with escaped keys and values; unsupported JSON values and non-finite numbers are errors. HTML is not escaped: when generating HTML, provide host escaping functions appropriate to the output context.

For compatibility, render and renderFromResource return Result.Success on success but throw syntax and runtime errors; they do not return Result.Error. Syntax errors include LexerError and LanguageError (both implement ParserError); malformed low-level input can also throw StreamError. Runtime errors use KoteRuntimeException. Loader and host-function exceptions, including coroutine cancellation, propagate. getValueOrNull() does not catch them.

Templates are intended for trusted input. The import guard is not a sandbox: there is no budget for general AST recursion, execution steps or output size. Host functions have the permissions of the application. Compilation caching and a compile/render API are future work.

Use JDK 21 to build and test. The published JVM library requires Java 11 or newer. Gradle 9.7.0 and Kotlin 2.4.20 are pinned in the build.

Update the default library version for each new change set: use the next patch version for fixes and the next minor version for features or pre-1.0 behavior changes. Use the final version directly, without a -SNAPSHOT suffix.

See ROADMAP.md for planned milestones and their acceptance criteria.

./gradlew jvmTest jsNodeTest nativeTest
./gradlew build
./gradlew dependencyUpdates

Gradle downloads Node.js and Kotlin/Native toolchains as needed. Commit the JS dependency lock file; after an intentional dependency update, run ./gradlew kotlinUpgradeYarnLock.

PRs and pushes to master run CI without publishing credentials. A v<version> tag triggers the release workflow, which tests the tagged source, signs artifacts and uploads them to Central Portal and GitHub Packages. The tag supplies the version through -PreleaseVersion; do not reuse a published version.

Configure these repository secrets before releasing:

• MAVEN_CENTRAL_USERNAME and MAVEN_CENTRAL_PASSWORD: a Central Portal user token for the verified dev.limebeck namespace, not the retired OSSRH credentials.
• SIGNING_KEY: the ASCII-armored private GPG key (not the former encrypted/base64 key file).
• SIGNING_PASSWORD and, if needed, SIGNING_KEY_ID: its passphrase and key ID.

The public signing key must be available to Central. The workflow uses an in-memory key and leaves the Central deployment for manual release after validation in the Portal. Actual account, namespace and credential validation requires an authorized release and is not part of local tests. See Central publishing setup.