diff --git a/README.md b/README.md
index 552e071..e8e60cf 100644
--- a/README.md
+++ b/README.md
@@ -132,13 +132,13 @@ If you want to write AI agents, you need tools, and this is where this library s
 ```kotlin
 @AnthropicTool("get_weather")
 @Description("Get the weather for a specific location")
-data class WeatherTool(val location: String): ToolInput {
-  override fun use(
-    toolUseId: String
-  ) = ToolResult(
-    toolUseId,
-    "The weather is 73f" // it should use some external service
-  )
+data class WeatherTool(val location: String): ToolInput() {
+  init {
+    use {
+      // in the real world it should use some external service
+      +"The weather is 73f"
+    }
+  }
 }
 
 fun main() = runBlocking {
@@ -192,21 +192,20 @@ internet or DB connection pool to access the database.
 ```kotlin
 @AnthropicTool("query_database")
 @Description("Executes SQL on the database")
-data class QueryDatabase(val sql: String): ToolInput {
+data class QueryDatabase(val sql: String): ToolInput() {
 
   @Transient
   internal lateinit var connection: Connection
 
-  override fun use(
-    toolUseId: String
-  ) = ToolResult(
-    toolUseId,
-    text = connection.prepareStatement(sql).use { statement ->
-      statement.resultSet.use { resultSet ->
-        resultSet.toString()
+  init {
+    use {
+      +connection.prepareStatement(sql).use { statement ->
+        statement.executeQuery().use { resultSet ->
+          resultSet.toString()
+        }
       }
     }
-  )
+  }
 
 }
 
diff --git a/src/commonMain/kotlin/Anthropic.kt b/src/commonMain/kotlin/Anthropic.kt
index 347f619..65fef1d 100644
--- a/src/commonMain/kotlin/Anthropic.kt
+++ b/src/commonMain/kotlin/Anthropic.kt
@@ -95,6 +95,7 @@ class Anthropic internal constructor(
 
     var tools: List<Tool> = emptyList()
 
+    // TODO in the future this should be rather Tool builder
     inline fun <reified T : ToolInput> tool(
       cacheControl: CacheControl? = null,
       noinline inputInitializer: T.() -> Unit = {}
diff --git a/src/commonMain/kotlin/content/ContentBuilder.kt b/src/commonMain/kotlin/content/ContentBuilder.kt
new file mode 100644
index 0000000..777e532
--- /dev/null
+++ b/src/commonMain/kotlin/content/ContentBuilder.kt
@@ -0,0 +1,25 @@
+package com.xemantic.anthropic.content
+
+import com.xemantic.anthropic.message.Content
+
+interface ContentBuilder {
+
+  val content: MutableList<Content>
+
+  operator fun Content.unaryPlus() {
+    content += this
+  }
+
+  operator fun String.unaryPlus() {
+    content += Text(this)
+  }
+
+  operator fun Number.unaryPlus() {
+    content += Text(this.toString())
+  }
+
+  operator fun Collection<Content>.unaryPlus() {
+    content += this
+  }
+
+}
diff --git a/src/commonMain/kotlin/content/Tool.kt b/src/commonMain/kotlin/content/Tool.kt
index a5f823e..5c2e7de 100644
--- a/src/commonMain/kotlin/content/Tool.kt
+++ b/src/commonMain/kotlin/content/Tool.kt
@@ -10,7 +10,6 @@ import kotlinx.serialization.SerialName
 import kotlinx.serialization.Serializable
 import kotlinx.serialization.Transient
 import kotlinx.serialization.json.JsonObject
-import kotlin.collections.plus
 import kotlin.contracts.ExperimentalContracts
 import kotlin.contracts.InvocationKind
 import kotlin.contracts.contract
@@ -69,35 +68,24 @@ data class ToolResult(
   override val cacheControl: CacheControl? = null
 ) : Content() {
 
-  class Builder {
+  class Builder : ContentBuilder {
+
+    override val content: MutableList<Content> = mutableListOf()
 
-    var content: List<Content> = emptyList()
     var isError: Boolean? = null
     var cacheControl: CacheControl? = null
 
-    fun content(message: String) {
-      content = listOf(Text(text = message))
-    }
-
     fun error(message: String) {
-      content(message)
+      +message
       isError = true
     }
 
-    operator fun List<Content>.unaryPlus() {
-      content += this
-    }
-
-    operator fun String.unaryPlus() {
-      content(this)
-    }
-
   }
 
 }
 
 @OptIn(ExperimentalContracts::class)
-fun ToolResult(
+inline fun ToolResult(
   toolUseId: String,
   block: ToolResult.Builder.() -> Unit = {}
 ): ToolResult {
@@ -105,7 +93,7 @@ fun ToolResult(
     callsInPlace(block, InvocationKind.EXACTLY_ONCE)
   }
   val builder = ToolResult.Builder()
-  builder.apply(block)
+  block(builder)
   return ToolResult(
     toolUseId = toolUseId,
     content = builder.content.toNullIfEmpty(),
diff --git a/src/commonMain/kotlin/message/Messages.kt b/src/commonMain/kotlin/message/Messages.kt
index f37343b..d463600 100644
--- a/src/commonMain/kotlin/message/Messages.kt
+++ b/src/commonMain/kotlin/message/Messages.kt
@@ -3,7 +3,7 @@ package com.xemantic.anthropic.message
 import com.xemantic.anthropic.Model
 import com.xemantic.anthropic.Response
 import com.xemantic.anthropic.cache.CacheControl
-import com.xemantic.anthropic.content.Text
+import com.xemantic.anthropic.content.ContentBuilder
 import com.xemantic.anthropic.tool.Tool
 import com.xemantic.anthropic.tool.ToolChoice
 import com.xemantic.anthropic.tool.ToolInput
@@ -176,21 +176,11 @@ data class Message(
   val content: List<Content>
 ) {
 
-  class Builder {
-    var role = Role.USER
-    val content = mutableListOf<Content>()
-
-    operator fun Content.unaryPlus() {
-      content += this
-    }
+  class Builder : ContentBuilder {
 
-    operator fun List<Content>.unaryPlus() {
-      content += this
-    }
+    override val content = mutableListOf<Content>()
 
-    operator fun String.unaryPlus() {
-      content += Text(this)
-    }
+    var role = Role.USER
 
     fun build() = Message(
       role = role,
diff --git a/src/commonMain/kotlin/tool/Tools.kt b/src/commonMain/kotlin/tool/Tools.kt
index 2742e86..166fee0 100644
--- a/src/commonMain/kotlin/tool/Tools.kt
+++ b/src/commonMain/kotlin/tool/Tools.kt
@@ -33,13 +33,6 @@ abstract class Tool {
   @PublishedApi
   internal lateinit var inputInitializer: ToolInput.() -> Unit
 
-  inline fun <reified T: ToolInput> initialize(
-    noinline block: T.() -> Unit
-  ) {
-    @Suppress("UNCHECKED_CAST")
-    inputInitializer = block as ToolInput.() -> Unit
-  }
-
 }
 
 @Serializable
@@ -73,7 +66,13 @@ abstract class BuiltInTool(
  * with a given tool use ID. The implementation of the [use] method should
  * contain the logic for executing the tool and returning the [ToolResult].
  */
-interface ToolInput {
+abstract class ToolInput() {
+
+  private lateinit var block: suspend ToolResult.Builder.() -> Unit
+
+  fun use(block: suspend ToolResult.Builder.() -> Unit) {
+    this.block = block
+  }
 
   /**
    * Executes the tool and returns the result.
@@ -81,7 +80,11 @@ interface ToolInput {
    * @param toolUseId A unique identifier for this particular use of the tool.
    * @return A [ToolResult] containing the outcome of executing the tool.
    */
-  suspend fun use(toolUseId: String): ToolResult
+  suspend fun use(toolUseId: String): ToolResult {
+    return ToolResult(toolUseId) {
+      block(this)
+    }
+  }
 
 }
 
diff --git a/src/commonMain/kotlin/tool/bash/Bash.kt b/src/commonMain/kotlin/tool/bash/Bash.kt
index 203840b..45f8387 100644
--- a/src/commonMain/kotlin/tool/bash/Bash.kt
+++ b/src/commonMain/kotlin/tool/bash/Bash.kt
@@ -1,7 +1,6 @@
 package com.xemantic.anthropic.tool.bash
 
 import com.xemantic.anthropic.cache.CacheControl
-import com.xemantic.anthropic.content.ToolResult
 import com.xemantic.anthropic.tool.BuiltInTool
 import com.xemantic.anthropic.tool.ToolInput
 import kotlinx.serialization.ExperimentalSerializationApi
@@ -22,10 +21,12 @@ data class Bash(
   data class Input(
     val command: String,
     val restart: Boolean? = false,
-  ) : ToolInput {
+  ) : ToolInput() {
 
-    override suspend fun use(toolUseId: String): ToolResult {
-      TODO("Not yet implemented")
+    init {
+      use {
+        TODO("Not yet implemented")
+      }
     }
 
   }
diff --git a/src/commonMain/kotlin/tool/computer/Computer.kt b/src/commonMain/kotlin/tool/computer/Computer.kt
index 9f113a0..8270e6c 100644
--- a/src/commonMain/kotlin/tool/computer/Computer.kt
+++ b/src/commonMain/kotlin/tool/computer/Computer.kt
@@ -1,7 +1,7 @@
 package com.xemantic.anthropic.tool.computer
 
 import com.xemantic.anthropic.cache.CacheControl
-import com.xemantic.anthropic.content.ToolResult
+import com.xemantic.anthropic.content.Image
 import com.xemantic.anthropic.tool.BuiltInTool
 import com.xemantic.anthropic.tool.ToolInput
 import kotlinx.serialization.ExperimentalSerializationApi
@@ -27,9 +27,6 @@ data class Computer(
 
   init {
     inputSerializer = Input.serializer()
-    initialize<Input> {
-      service = computerService
-    }
   }
 
   @Serializable
@@ -37,14 +34,19 @@ data class Computer(
     val action: Action,
     val coordinate: Coordinate?,
     val text: String
-  ) : ToolInput {
+  ) : ToolInput() {
 
     @Transient
     lateinit var service: ComputerService
 
-    override suspend fun use(
-      toolUseId: String
-    ) = service.use(toolUseId, this)
+    init {
+      use {
+        when (action) {
+          Action.SCREENSHOT -> +service.screenshot()
+          else -> TODO("Not implemented yet")
+        }
+      }
+    }
 
   }
 
@@ -81,11 +83,6 @@ data class Coordinate(val x: Int, val y: Int)
 
 interface ComputerService {
 
-  suspend fun use(
-    toolUseId: String,
-    input: Computer.Input
-  ): ToolResult
+  fun screenshot(): Image
 
 }
-
-expect val computerService: ComputerService
diff --git a/src/commonMain/kotlin/tool/editor/TextEditor.kt b/src/commonMain/kotlin/tool/editor/TextEditor.kt
index f0c616d..dac8d91 100644
--- a/src/commonMain/kotlin/tool/editor/TextEditor.kt
+++ b/src/commonMain/kotlin/tool/editor/TextEditor.kt
@@ -1,7 +1,6 @@
 package com.xemantic.anthropic.tool.editor
 
 import com.xemantic.anthropic.cache.CacheControl
-import com.xemantic.anthropic.content.ToolResult
 import com.xemantic.anthropic.tool.BuiltInTool
 import com.xemantic.anthropic.tool.ToolInput
 import kotlinx.serialization.ExperimentalSerializationApi
@@ -21,9 +20,6 @@ data class TextEditor(
 
   init {
     inputSerializer = Input.serializer()
-    inputInitializer = {
-      //service = computerService
-    }
   }
 
   @Serializable
@@ -41,14 +37,19 @@ data class TextEditor(
     val path: String,
     @SerialName("view_range")
     val viewRange: Int? = 0
-  ) : ToolInput {
+  ) : ToolInput() {
 
     @Transient
     lateinit var service: TextEditorService
 
-    override suspend fun use(
-      toolUseId: String
-    ) = service.use(toolUseId, this)
+    init {
+      use {
+        when (command) {
+          Command.VIEW -> service.view(path)
+          else -> TODO("not implemented yet")
+        }
+      }
+    }
 
   }
 
@@ -70,11 +71,6 @@ enum class Command {
 
 interface TextEditorService {
 
-  suspend fun use(
-    toolUseId: String,
-    input: TextEditor.Input
-  ): ToolResult
+  fun view(path: String)
 
 }
-
-expect val textEditorService: TextEditorService
diff --git a/src/commonTest/kotlin/message/MessageRequestTest.kt b/src/commonTest/kotlin/message/MessageRequestTest.kt
index dafbff4..3525067 100644
--- a/src/commonTest/kotlin/message/MessageRequestTest.kt
+++ b/src/commonTest/kotlin/message/MessageRequestTest.kt
@@ -1,6 +1,5 @@
 package com.xemantic.anthropic.message
 
-import com.xemantic.anthropic.content.ToolResult
 import com.xemantic.anthropic.message.MessageRequestTest.TemperatureUnit
 import com.xemantic.anthropic.schema.Description
 import com.xemantic.anthropic.test.testJson
@@ -25,12 +24,12 @@ data class GetWeather(
   val location: String,
   @Description("The unit of temperature, either 'celsius' or 'fahrenheit'")
   val unit: TemperatureUnit? = null
-) : ToolInput {
-
-  override suspend fun use(
-    toolUseId: String
-  ) = ToolResult(toolUseId) { +"42" }
-
+) : ToolInput() {
+  init {
+    use {
+      +"42"
+    }
+  }
 }
 
 /**
diff --git a/src/commonTest/kotlin/tool/AnthropicTestTools.kt b/src/commonTest/kotlin/tool/AnthropicTestTools.kt
index 74d32d1..7dc3c60 100644
--- a/src/commonTest/kotlin/tool/AnthropicTestTools.kt
+++ b/src/commonTest/kotlin/tool/AnthropicTestTools.kt
@@ -1,25 +1,22 @@
 package com.xemantic.anthropic.tool
 
-import com.xemantic.anthropic.content.ToolResult
 import com.xemantic.anthropic.schema.Description
 import kotlinx.serialization.Transient
 
+tailrec fun fibonacci(
+  n: Int, a: Int = 0, b: Int = 1
+): Int = when (n) {
+  0 -> a; 1 -> b; else -> fibonacci(n - 1, b, a + b)
+}
+
 @AnthropicTool("FibonacciTool")
 @Description("Calculate Fibonacci number n")
-data class FibonacciTool(val n: Int): ToolInput {
-
-  tailrec fun fibonacci(
-    n: Int, a: Int = 0, b: Int = 1
-  ): Int = when (n) {
-    0 -> a; 1 -> b; else -> fibonacci(n - 1, b, a + b)
-  }
-
-  override suspend fun use(
-    toolUseId: String,
-  ) = ToolResult(toolUseId) {
-    +"${fibonacci(n)}"
+data class FibonacciTool(val n: Int) : ToolInput() {
+  init {
+    use {
+      +fibonacci(n)
+    }
   }
-
 }
 
 @AnthropicTool("Calculator")
@@ -28,7 +25,7 @@ data class Calculator(
   val operation: Operation,
   val a: Double,
   val b: Double
-): ToolInput {
+): ToolInput() {
 
   @Suppress("unused") // it is used, but by Anthropic, so we skip the warning
   enum class Operation(
@@ -40,8 +37,10 @@ data class Calculator(
     DIVIDE({ a, b -> a / b })
   }
 
-  override suspend fun use(toolUseId: String) = ToolResult(toolUseId) {
-    +operation.calculate(a, b).toString()
+  init {
+    use {
+      +operation.calculate(a, b)
+    }
   }
 
 }
@@ -64,17 +63,14 @@ class TestDatabase : Database {
 @Description("Executes database query")
 data class DatabaseQuery(
   val query: String
-) : ToolInput {
+) : ToolInput() {
 
   @Transient
   internal lateinit var database: Database
 
-  override suspend fun use(
-    toolUseId: String
-  ): ToolResult {
-    val result = database.execute(query).joinToString()
-    return ToolResult(toolUseId) {
-      +result
+  init {
+    use {
+      +database.execute(query).joinToString()
     }
   }
 
diff --git a/src/commonTest/kotlin/tool/ToolInputTest.kt b/src/commonTest/kotlin/tool/ToolInputTest.kt
index c6b290f..3f3a3e9 100644
--- a/src/commonTest/kotlin/tool/ToolInputTest.kt
+++ b/src/commonTest/kotlin/tool/ToolInputTest.kt
@@ -1,7 +1,6 @@
 package com.xemantic.anthropic.tool
 
 import com.xemantic.anthropic.cache.CacheControl
-import com.xemantic.anthropic.content.ToolResult
 import com.xemantic.anthropic.schema.Description
 import com.xemantic.anthropic.schema.JsonSchema
 import com.xemantic.anthropic.schema.JsonSchemaProperty
@@ -19,10 +18,12 @@ class ToolInputTest {
   class TestToolInput(
     @Description("the message")
     val message: String
-  ) : ToolInput {
-    override suspend fun use(
-      toolUseId: String
-    ) = ToolResult(toolUseId) { +message }
+  ) : ToolInput() {
+    init {
+      use {
+        +message
+      }
+    }
   }
 
   @Test
@@ -66,11 +67,7 @@ class ToolInputTest {
     }
   }
 
-  class NoAnnotationTool : ToolInput {
-    override suspend fun use(
-      toolUseId: String
-    ) = ToolResult(toolUseId)
-  }
+  class NoAnnotationTool : ToolInput()
 
   @Test
   fun shouldFailToCreateToolWithoutAnthropicToolAnnotation() {
@@ -83,11 +80,7 @@ class ToolInputTest {
   }
 
   @Serializable
-  class OnlySerializableAnnotationTool : ToolInput {
-    override suspend fun use(
-      toolUseId: String
-    ) = ToolResult(toolUseId)
-  }
+  class OnlySerializableAnnotationTool : ToolInput()
 
   @Test
   fun shouldFailToCreateToolWithOnlySerializableAnnotation() {
diff --git a/src/jvmMain/kotlin/tool/computer/JvmComputer.kt b/src/jvmMain/kotlin/tool/computer/JvmComputer.kt
index e1338cd..60df2c1 100644
--- a/src/jvmMain/kotlin/tool/computer/JvmComputer.kt
+++ b/src/jvmMain/kotlin/tool/computer/JvmComputer.kt
@@ -1,7 +1,6 @@
 package com.xemantic.anthropic.tool.computer
 
 import com.xemantic.anthropic.content.Image
-import com.xemantic.anthropic.content.ToolResult
 import java.awt.Rectangle
 import java.awt.Robot
 import java.awt.Toolkit
@@ -10,20 +9,9 @@ import javax.imageio.ImageIO
 
 object JvmComputerService : ComputerService {
 
-  override suspend fun use(
-    toolUseId: String,
-    input: Computer.Input
-  ) = when (input.action) {
-    Action.SCREENSHOT -> ToolResult(
-      toolUseId = toolUseId,
-      content = listOf(
-        Image {
-          data = takeScreenshot()
-          mediaType = Image.MediaType.IMAGE_JPEG
-        }
-      )
-    )
-    else -> TODO()
+  override fun screenshot() = Image {
+    data = takeScreenshot()
+    mediaType = Image.MediaType.IMAGE_JPEG
   }
 
 }
@@ -38,5 +26,3 @@ fun takeScreenshot(): ByteArray {
   }
   return output.toByteArray()
 }
-
-actual val computerService: ComputerService get() = JvmComputerService
diff --git a/src/jvmMain/kotlin/tool/editor/JvmTextEditor.kt b/src/jvmMain/kotlin/tool/editor/JvmTextEditor.kt
index 6690b25..003a65b 100644
--- a/src/jvmMain/kotlin/tool/editor/JvmTextEditor.kt
+++ b/src/jvmMain/kotlin/tool/editor/JvmTextEditor.kt
@@ -1,24 +1,9 @@
 package com.xemantic.anthropic.tool.editor
 
-import com.xemantic.anthropic.content.ToolResult
-import java.io.File
-
 object JvmTextEditorService : TextEditorService {
 
-  override suspend fun use(
-    toolUseId: String,
-    input: TextEditor.Input
-  ): ToolResult {
-    val content = if (input.command == Command.VIEW) {
-      File(input.path).readText()
-    } else {
-      TODO("Not implemented yet")
-    }
-    return ToolResult(toolUseId) {
-      content(content)
-    }
+  override fun view(path: String) {
+    TODO("Not yet implemented")
   }
 
 }
-
-actual val textEditorService: TextEditorService get() = JvmTextEditorService