MyResource.java

package sandbox;

import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.core.MediaType;

import org.eclipse.microprofile.openapi.annotations.responses.APIResponse;

@Path("/")
public class MyResource {
	@GET
	@Produces(MediaType.TEXT_PLAIN)
	@APIResponse(responseCode = "200", description = "It did something!")
	public String get() {
		return "It worked!";
	}
}

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<groupId>acme</groupId>
	<artifactId>sandbox</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<packaging>war</packaging>

	<properties>
		<maven.compiler.source>1.8</maven.compiler.source>
		<maven.compiler.target>1.8</maven.compiler.target>
		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
		<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
		<failOnMissingWebXml>false</failOnMissingWebXml>
		<wildfly.swarm.version>2018.3.3</wildfly.swarm.version>
	</properties>

	<dependencyManagement>
		<dependencies>
			<dependency>
				<groupId>org.wildfly.swarm</groupId>
				<artifactId>bom-all</artifactId>
				<version>${wildfly.swarm.version}</version>
				<type>pom</type>
				<scope>import</scope>
			</dependency>
		</dependencies>
	</dependencyManagement>

	<dependencies>
		<dependency>
			<groupId>org.wildfly.swarm</groupId>
			<artifactId>jaxrs</artifactId>
		</dependency>
		<dependency>
			<groupId>org.wildfly.swarm</groupId>
			<artifactId>cdi</artifactId>
		</dependency>
		<dependency>
			<groupId>org.wildfly.swarm</groupId>
			<artifactId>microprofile-openapi</artifactId>
		</dependency>
	</dependencies>

	<build>
		<plugins>
			<plugin>
				<groupId>org.wildfly.swarm</groupId>
				<artifactId>wildfly-swarm-plugin</artifactId>
				<version>${wildfly.swarm.version}</version>
				<executions>
					<execution>
						<goals>
							<goal>package</goal>
						</goals>
					</execution>
				</executions>
			</plugin>
		</plugins>
	</build>
</project>