diff --git a/js/llm.ts b/js/llm.ts
index a32b513..a20e161 100644
--- a/js/llm.ts
+++ b/js/llm.ts
@@ -9,6 +9,7 @@ import {
   ChatCompletionTool,
 } from "openai/resources";
 import { makePartial, ScorerWithPartial } from "./partial";
+import { renderMessages } from "./render-messages";
 
 const NO_COT_SUFFIX =
   "Answer the question by calling `select_choice` with a single choice from {{__choices}}.";
@@ -118,15 +119,7 @@ export async function OpenAIClassifier<RenderArgs, Output>(
     ...remainingRenderArgs,
   };
 
-  const messages: ChatCompletionMessageParam[] = messagesArg.map((m) => ({
-    ...m,
-    content: m.content
-      ? mustache.render(m.content as string, renderArgs, undefined, {
-          escape: (v: unknown) =>
-            typeof v === "string" ? v : JSON.stringify(v),
-        })
-      : "",
-  }));
+  const messages = renderMessages(messagesArg, renderArgs);
 
   const resp = await cachedChatCompletion(
     {
diff --git a/js/render-messages.test.ts b/js/render-messages.test.ts
new file mode 100644
index 0000000..667af2c
--- /dev/null
+++ b/js/render-messages.test.ts
@@ -0,0 +1,35 @@
+import { renderMessages } from "./render-messages";
+import { ChatCompletionMessageParam } from "openai/resources";
+
+describe("renderMessages", () => {
+  it("should never HTML-escape values, regardless of mustache syntax", () => {
+    const messages: ChatCompletionMessageParam[] = [
+      { role: "user", content: "{{value}} and {{{value}}}" },
+    ];
+    const rendered = renderMessages(messages, { value: "<b>bold</b>" });
+    expect(rendered[0].content).toBe("<b>bold</b> and <b>bold</b>");
+  });
+
+  it("should stringify objects when using either {{...}} or {{{...}}}", () => {
+    const messages: ChatCompletionMessageParam[] = [
+      {
+        role: "user",
+        content: "Double braces: {{data}}, Triple braces: {{{data}}}",
+      },
+    ];
+    const data = { foo: "bar", num: 42 };
+    const rendered = renderMessages(messages, { data });
+    const stringified = JSON.stringify(data);
+    expect(rendered[0].content).toBe(
+      `Double braces: ${stringified}, Triple braces: ${stringified}`,
+    );
+  });
+
+  it("should handle empty content", () => {
+    const messages: ChatCompletionMessageParam[] = [
+      { role: "user", content: "" },
+    ];
+    const rendered = renderMessages(messages, {});
+    expect(rendered[0].content).toBe("");
+  });
+});
diff --git a/js/render-messages.ts b/js/render-messages.ts
new file mode 100644
index 0000000..e0f0bbe
--- /dev/null
+++ b/js/render-messages.ts
@@ -0,0 +1,22 @@
+import mustache from "mustache";
+import { ChatCompletionMessageParam } from "openai/resources";
+
+export function renderMessages(
+  messages: ChatCompletionMessageParam[],
+  renderArgs: Record<string, unknown>,
+): ChatCompletionMessageParam[] {
+  return messages.map((m) => ({
+    ...m,
+    content: m.content
+      ? mustache.render(
+          (m.content as string).replace(/\{{3}/g, "{{").replace(/\}{3}/g, "}}"),
+          renderArgs,
+          undefined,
+          {
+            escape: (v: unknown) =>
+              typeof v === "string" ? v : JSON.stringify(v),
+          },
+        )
+      : "",
+  }));
+}
diff --git a/py/autoevals/test_llm.py b/py/autoevals/test_llm.py
index 12ec823..5af71c2 100644
--- a/py/autoevals/test_llm.py
+++ b/py/autoevals/test_llm.py
@@ -5,12 +5,54 @@
 import chevron
 import pytest
 import respx
+from pydantic import BaseModel
 
 from autoevals import init
 from autoevals.llm import *
 from autoevals.llm import build_classification_tools
 
 
+class TestModel(BaseModel):
+    foo: str
+    num: int
+
+
+def test_render_messages():
+    classifier = OpenAILLMClassifier(
+        "test",
+        messages=[
+            {"role": "user", "content": "{{value}} and {{{value}}}"},
+            {"role": "user", "content": "Dict double braces: {{data}}"},
+            {"role": "user", "content": "Dict triple braces: {{{data}}}"},
+            {"role": "user", "content": "Model double braces: {{model}}"},
+            {"role": "user", "content": "Model triple braces: {{{model}}}"},
+            {"role": "user", "content": ""},  # test empty content
+        ],
+        model="gpt-4",
+        choice_scores={"A": 1},
+        classification_tools=[],
+    )
+
+    test_dict = {"foo": "bar", "num": 42}
+    test_model = TestModel(foo="bar", num=42)
+
+    rendered = classifier._render_messages(value="<b>bold</b>", data=test_dict, model=test_model)
+
+    # Test HTML escaping - double braces escape, triple braces don't.
+    assert rendered[0]["content"] == "&lt;b&gt;bold&lt;/b&gt; and <b>bold</b>"
+
+    # Test dict rendering - both use str() but double braces escape HTML chars if present.
+    assert rendered[1]["content"] == "Dict double braces: {'foo': 'bar', 'num': 42}"
+    assert rendered[2]["content"] == "Dict triple braces: {'foo': 'bar', 'num': 42}"
+
+    # Test model rendering - both use str() but double braces escape HTML chars if present.
+    assert rendered[3]["content"] == "Model double braces: foo='bar' num=42"
+    assert rendered[4]["content"] == "Model triple braces: foo='bar' num=42"
+
+    # Test empty content.
+    assert rendered[5]["content"] == ""
+
+
 def test_template_html():
     template_double = "{{output}}"
     template_triple = "{{{output}}}"