diff --git a/examples/basic/src/model-provider/llamacpp/llamacpp-run-tool-mistral-example.ts b/examples/basic/src/model-provider/llamacpp/llamacpp-run-tool-mistral-example.ts
new file mode 100644
index 00000000..2798a17b
--- /dev/null
+++ b/examples/basic/src/model-provider/llamacpp/llamacpp-run-tool-mistral-example.ts
@@ -0,0 +1,28 @@
+import { jsonToolCallPrompt, llamacpp, runTool } from "modelfusion";
+import { calculator } from "../../tool/tools/calculator-tool";
+
+async function main() {
+  const { tool, toolCall, args, ok, result } = await runTool({
+    model: llamacpp
+      .CompletionTextGenerator({
+        // run https://huggingface.co/TheBloke/Mistral-7B-Instruct-v0.2-GGUF with llama.cpp
+        promptTemplate: llamacpp.prompt.ChatML,
+        temperature: 0,
+      })
+      .withInstructionPrompt()
+      .asToolCallGenerationModel(jsonToolCallPrompt.text()),
+
+    tool: calculator,
+    prompt: "What's fourteen times twelve?",
+
+    logging: "detailed-object",
+  });
+
+  console.log(`Tool call:`, toolCall);
+  console.log(`Tool:`, tool);
+  console.log(`Arguments:`, args);
+  console.log(`Ok:`, ok);
+  console.log(`Result or Error:`, result);
+}
+
+main().catch(console.error);
diff --git a/packages/modelfusion/src/model-function/generate-object/jsonObjectPrompt.ts b/packages/modelfusion/src/model-function/generate-object/jsonObjectPrompt.ts
index a5707c40..144421e1 100644
--- a/packages/modelfusion/src/model-function/generate-object/jsonObjectPrompt.ts
+++ b/packages/modelfusion/src/model-function/generate-object/jsonObjectPrompt.ts
@@ -9,7 +9,7 @@ import {
 
 const DEFAULT_SCHEMA_PREFIX = "JSON schema:";
 const DEFAULT_SCHEMA_SUFFIX =
-  "\nYou MUST answer with a JSON object matches the above schema.";
+  "\nYou MUST answer with a JSON object that matches the JSON schema above.";
 
 export const jsonObjectPrompt = {
   custom<SOURCE_PROMPT, TARGET_PROMPT>(
@@ -85,6 +85,7 @@ function createSystemPrompt({
 }) {
   return [
     originalSystemPrompt,
+    originalSystemPrompt != null ? "" : null,
     schemaPrefix,
     JSON.stringify(schema.getJsonSchema()),
     schemaSuffix,
diff --git a/packages/modelfusion/src/model-function/generate-text/PromptTemplateTextGenerationModel.ts b/packages/modelfusion/src/model-function/generate-text/PromptTemplateTextGenerationModel.ts
index 554df53f..f1c46c78 100644
--- a/packages/modelfusion/src/model-function/generate-text/PromptTemplateTextGenerationModel.ts
+++ b/packages/modelfusion/src/model-function/generate-text/PromptTemplateTextGenerationModel.ts
@@ -1,10 +1,8 @@
 import { FunctionCallOptions } from "../../core/FunctionOptions";
 import { JsonSchemaProducer } from "../../core/schema/JsonSchemaProducer";
 import { Schema } from "../../core/schema/Schema";
-import {
-  TextGenerationToolCallModel,
-  ToolCallPromptTemplate,
-} from "../../tool/generate-tool-call/TextGenerationToolCallModel";
+import { TextGenerationToolCallModel } from "../../tool/generate-tool-call/TextGenerationToolCallModel";
+import { ToolCallPromptTemplate } from "../../tool/generate-tool-call/ToolCallPromptTemplate";
 import { TextGenerationToolCallsModel } from "../../tool/generate-tool-calls/TextGenerationToolCallsModel";
 import { ToolCallsPromptTemplate } from "../../tool/generate-tool-calls/ToolCallsPromptTemplate";
 import { ObjectFromTextGenerationModel } from "../generate-object/ObjectFromTextGenerationModel";
@@ -91,7 +89,7 @@ export class PromptTemplateTextGenerationModel<
   ) {
     return new TextGenerationToolCallModel({
       model: this,
-      format: promptTemplate,
+      template: promptTemplate,
     });
   }
 
diff --git a/packages/modelfusion/src/model-provider/ollama/OllamaChatModel.ts b/packages/modelfusion/src/model-provider/ollama/OllamaChatModel.ts
index b592d960..8277703e 100644
--- a/packages/modelfusion/src/model-provider/ollama/OllamaChatModel.ts
+++ b/packages/modelfusion/src/model-provider/ollama/OllamaChatModel.ts
@@ -20,10 +20,8 @@ import {
   textGenerationModelProperties,
 } from "../../model-function/generate-text/TextGenerationModel";
 import { TextGenerationPromptTemplate } from "../../model-function/generate-text/TextGenerationPromptTemplate";
-import {
-  TextGenerationToolCallModel,
-  ToolCallPromptTemplate,
-} from "../../tool/generate-tool-call/TextGenerationToolCallModel";
+import { TextGenerationToolCallModel } from "../../tool/generate-tool-call/TextGenerationToolCallModel";
+import { ToolCallPromptTemplate } from "../../tool/generate-tool-call/ToolCallPromptTemplate";
 import { TextGenerationToolCallsModel } from "../../tool/generate-tool-calls/TextGenerationToolCallsModel";
 import { ToolCallsPromptTemplate } from "../../tool/generate-tool-calls/ToolCallsPromptTemplate";
 import { createJsonStreamResponseHandler } from "../../util/streaming/createJsonStreamResponseHandler";
@@ -198,7 +196,7 @@ export class OllamaChatModel
   ) {
     return new TextGenerationToolCallModel({
       model: this,
-      format: promptTemplate,
+      template: promptTemplate,
     });
   }
 
diff --git a/packages/modelfusion/src/model-provider/ollama/OllamaCompletionModel.ts b/packages/modelfusion/src/model-provider/ollama/OllamaCompletionModel.ts
index a5b469f0..79dfde94 100644
--- a/packages/modelfusion/src/model-provider/ollama/OllamaCompletionModel.ts
+++ b/packages/modelfusion/src/model-provider/ollama/OllamaCompletionModel.ts
@@ -23,10 +23,8 @@ import { TextGenerationPromptTemplate } from "../../model-function/generate-text
 import { ChatPrompt } from "../../model-function/generate-text/prompt-template/ChatPrompt";
 import { InstructionPrompt } from "../../model-function/generate-text/prompt-template/InstructionPrompt";
 import { TextGenerationPromptTemplateProvider } from "../../model-function/generate-text/prompt-template/PromptTemplateProvider";
-import {
-  TextGenerationToolCallModel,
-  ToolCallPromptTemplate,
-} from "../../tool/generate-tool-call/TextGenerationToolCallModel";
+import { TextGenerationToolCallModel } from "../../tool/generate-tool-call/TextGenerationToolCallModel";
+import { ToolCallPromptTemplate } from "../../tool/generate-tool-call/ToolCallPromptTemplate";
 import { TextGenerationToolCallsModel } from "../../tool/generate-tool-calls/TextGenerationToolCallsModel";
 import { ToolCallsPromptTemplate } from "../../tool/generate-tool-calls/ToolCallsPromptTemplate";
 import { createJsonStreamResponseHandler } from "../../util/streaming/createJsonStreamResponseHandler";
@@ -262,7 +260,7 @@ export class OllamaCompletionModel<
   ) {
     return new TextGenerationToolCallModel({
       model: this,
-      format: promptTemplate,
+      template: promptTemplate,
     });
   }
 
diff --git a/packages/modelfusion/src/tool/generate-tool-call/TextGenerationToolCallModel.ts b/packages/modelfusion/src/tool/generate-tool-call/TextGenerationToolCallModel.ts
index 6a7e9bd1..cede023a 100644
--- a/packages/modelfusion/src/tool/generate-tool-call/TextGenerationToolCallModel.ts
+++ b/packages/modelfusion/src/tool/generate-tool-call/TextGenerationToolCallModel.ts
@@ -1,23 +1,15 @@
 import { FunctionOptions } from "../../core/FunctionOptions";
+import { JsonSchemaProducer } from "../../core/schema/JsonSchemaProducer";
+import { Schema } from "../../core/schema/Schema";
 import {
   TextGenerationModel,
   TextGenerationModelSettings,
 } from "../../model-function/generate-text/TextGenerationModel";
 import { generateText } from "../../model-function/generate-text/generateText";
-import { ToolCallParseError } from "./ToolCallParseError";
 import { ToolDefinition } from "../ToolDefinition";
 import { ToolCallGenerationModel } from "./ToolCallGenerationModel";
-
-export interface ToolCallPromptTemplate<SOURCE_PROMPT, TARGET_PROMPT> {
-  createPrompt: (
-    prompt: SOURCE_PROMPT,
-    tool: ToolDefinition<string, unknown>
-  ) => TARGET_PROMPT;
-  extractToolCall: (
-    response: string,
-    tool: ToolDefinition<string, unknown>
-  ) => { id: string; args: unknown } | null;
-}
+import { ToolCallParseError } from "./ToolCallParseError";
+import { ToolCallPromptTemplate } from "./ToolCallPromptTemplate";
 
 export class TextGenerationToolCallModel<
   SOURCE_PROMPT,
@@ -26,17 +18,20 @@ export class TextGenerationToolCallModel<
 > implements ToolCallGenerationModel<SOURCE_PROMPT, MODEL["settings"]>
 {
   private readonly model: MODEL;
-  private readonly format: ToolCallPromptTemplate<SOURCE_PROMPT, TARGET_PROMPT>;
+  private readonly template: ToolCallPromptTemplate<
+    SOURCE_PROMPT,
+    TARGET_PROMPT
+  >;
 
   constructor({
     model,
-    format,
+    template,
   }: {
     model: MODEL;
-    format: ToolCallPromptTemplate<SOURCE_PROMPT, TARGET_PROMPT>;
+    template: ToolCallPromptTemplate<SOURCE_PROMPT, TARGET_PROMPT>;
   }) {
     this.model = model;
-    this.format = format;
+    this.template = template;
   }
 
   get modelInformation() {
@@ -51,14 +46,25 @@ export class TextGenerationToolCallModel<
     return this.model.settingsForEvent;
   }
 
+  getModelWithJsonOutput(schema: Schema<unknown> & JsonSchemaProducer) {
+    if (this.template.withJsonOutput != null) {
+      return this.template.withJsonOutput({
+        model: this.model,
+        schema,
+      }) as MODEL;
+    }
+
+    return this.model;
+  }
+
   async doGenerateToolCall(
     tool: ToolDefinition<string, unknown>,
     prompt: SOURCE_PROMPT,
     options?: FunctionOptions
   ) {
     const { rawResponse, text, metadata } = await generateText({
-      model: this.model,
-      prompt: this.format.createPrompt(prompt, tool),
+      model: this.getModelWithJsonOutput(tool.parameters),
+      prompt: this.template.createPrompt(prompt, tool),
       fullResponse: true,
       ...options,
     });
@@ -66,7 +72,7 @@ export class TextGenerationToolCallModel<
     try {
       return {
         rawResponse,
-        toolCall: this.format.extractToolCall(text, tool),
+        toolCall: this.template.extractToolCall(text, tool),
         usage: metadata?.usage as
           | {
               promptTokens: number;
@@ -87,7 +93,7 @@ export class TextGenerationToolCallModel<
   withSettings(additionalSettings: Partial<MODEL["settings"]>): this {
     return new TextGenerationToolCallModel({
       model: this.model.withSettings(additionalSettings),
-      format: this.format,
+      template: this.template,
     }) as this;
   }
 }
diff --git a/packages/modelfusion/src/tool/generate-tool-call/ToolCallPromptTemplate.ts b/packages/modelfusion/src/tool/generate-tool-call/ToolCallPromptTemplate.ts
new file mode 100644
index 00000000..8736f233
--- /dev/null
+++ b/packages/modelfusion/src/tool/generate-tool-call/ToolCallPromptTemplate.ts
@@ -0,0 +1,27 @@
+import { JsonSchemaProducer } from "../../core/schema/JsonSchemaProducer";
+import { Schema } from "../../core/schema/Schema";
+import { ToolDefinition } from "../ToolDefinition";
+
+export interface ToolCallPromptTemplate<SOURCE_PROMPT, TARGET_PROMPT> {
+  createPrompt(
+    prompt: SOURCE_PROMPT,
+    tool: ToolDefinition<string, unknown>
+  ): TARGET_PROMPT;
+
+  extractToolCall(
+    response: string,
+    tool: ToolDefinition<string, unknown>
+  ): { id: string; args: unknown } | null;
+
+  withJsonOutput?({
+    model,
+    schema,
+  }: {
+    model: {
+      withJsonOutput(
+        schema: Schema<unknown> & JsonSchemaProducer
+      ): typeof model;
+    };
+    schema: Schema<unknown> & JsonSchemaProducer;
+  }): typeof model;
+}
diff --git a/packages/modelfusion/src/tool/generate-tool-call/index.ts b/packages/modelfusion/src/tool/generate-tool-call/index.ts
index 52fc5ab4..977bbea3 100644
--- a/packages/modelfusion/src/tool/generate-tool-call/index.ts
+++ b/packages/modelfusion/src/tool/generate-tool-call/index.ts
@@ -2,5 +2,6 @@ export * from "./TextGenerationToolCallModel";
 export * from "./ToolCallGenerationEvent";
 export * from "./ToolCallGenerationModel";
 export * from "./ToolCallParseError";
+export * from "./ToolCallPromptTemplate";
 export * from "./generateToolCall";
 export * from "./jsonToolCallPrompt";
diff --git a/packages/modelfusion/src/tool/generate-tool-call/jsonToolCallPrompt.ts b/packages/modelfusion/src/tool/generate-tool-call/jsonToolCallPrompt.ts
index 6a131f68..6638c6e5 100644
--- a/packages/modelfusion/src/tool/generate-tool-call/jsonToolCallPrompt.ts
+++ b/packages/modelfusion/src/tool/generate-tool-call/jsonToolCallPrompt.ts
@@ -2,33 +2,84 @@ import { nanoid } from "nanoid";
 import { parseJSON } from "../../core/schema/parseJSON";
 import { InstructionPrompt } from "../../model-function/generate-text/prompt-template/InstructionPrompt";
 import { ToolDefinition } from "../../tool/ToolDefinition";
-import { ToolCallPromptTemplate } from "./TextGenerationToolCallModel";
+import { ToolCallPromptTemplate } from "./ToolCallPromptTemplate";
+
+const DEFAULT_TOOL_PROMPT = (tool: ToolDefinition<string, unknown>) =>
+  [
+    `You are calling the function "${tool.name}".`,
+    tool.description != null
+      ? `Function description: ${tool.description}`
+      : null,
+    `Function parameters JSON schema: ${JSON.stringify(
+      tool.parameters.getJsonSchema()
+    )}`,
+    ``,
+    `You MUST answer with a JSON object that matches the JSON schema above.`,
+  ]
+    .filter(Boolean)
+    .join("\n");
 
 export const jsonToolCallPrompt = {
-  text(): ToolCallPromptTemplate<string, InstructionPrompt> {
+  text({
+    toolPrompt,
+  }: {
+    toolPrompt?: (tool: ToolDefinition<string, unknown>) => string;
+  } = {}): ToolCallPromptTemplate<string, InstructionPrompt> {
     return {
-      createPrompt(instruction: string, tool: ToolDefinition<string, unknown>) {
+      createPrompt(prompt: string, tool: ToolDefinition<string, unknown>) {
         return {
-          system: [
-            `You are calling a function "${tool.name}".`,
-            tool.description != null
-              ? `  Function description: ${tool.description}`
-              : null,
-            `  Function parameters JSON schema: ${JSON.stringify(
-              tool.parameters.getJsonSchema()
-            )}`,
-            ``,
-            `You MUST answer with a JSON object matches the above schema for the arguments.`,
-          ]
-            .filter(Boolean)
-            .join("\n"),
-          instruction,
+          system: createSystemPrompt({ tool, toolPrompt }),
+          instruction: prompt,
         };
       },
+      extractToolCall,
+      withJsonOutput: ({ model, schema }) => model.withJsonOutput(schema),
+    };
+  },
 
-      extractToolCall(response) {
-        return { id: nanoid(), args: parseJSON({ text: response }) };
+  instruction({
+    toolPrompt,
+  }: {
+    toolPrompt?: (tool: ToolDefinition<string, unknown>) => string;
+  } = {}): ToolCallPromptTemplate<InstructionPrompt, InstructionPrompt> {
+    return {
+      createPrompt(
+        prompt: InstructionPrompt,
+        tool: ToolDefinition<string, unknown>
+      ): InstructionPrompt {
+        return {
+          system: createSystemPrompt({
+            originalSystemPrompt: prompt.system,
+            tool,
+            toolPrompt,
+          }),
+          instruction: prompt.instruction,
+        };
       },
+      extractToolCall,
+      withJsonOutput: ({ model, schema }) => model.withJsonOutput(schema),
     };
   },
 };
+
+function createSystemPrompt({
+  originalSystemPrompt,
+  toolPrompt = DEFAULT_TOOL_PROMPT,
+  tool,
+}: {
+  originalSystemPrompt?: string;
+  toolPrompt?: (tool: ToolDefinition<string, unknown>) => string;
+  tool: ToolDefinition<string, unknown>;
+}) {
+  return [
+    originalSystemPrompt,
+    originalSystemPrompt != null ? "" : null,
+    toolPrompt(tool),
+  ]
+    .filter(Boolean)
+    .join("\n");
+}
+
+function extractToolCall(response: string) {
+  return { id: nanoid(), args: parseJSON({ text: response }) };
+}