diff --git a/packages/core/src/env.ts b/packages/core/src/env.ts
index 16c3171852..7834958112 100644
--- a/packages/core/src/env.ts
+++ b/packages/core/src/env.ts
@@ -69,6 +69,8 @@ import type { TraceOptions } from "./trace.js";
 import type { CancellationOptions } from "./cancellation.js";
 import { genaiscriptDebug } from "./debug.js";
 import { YAMLTryParse } from "./yaml.js";
+import { JSON5TryParse } from "./json5.js";
+import type { PromptArgs, PromptScript } from "./types.js";
 const dbg = genaiscriptDebug("config:env");
 
 /**
@@ -122,6 +124,50 @@ export function findEnvVar(
   return undefined;
 }
 
+/**
+ * Parses default script metadata from GENAISCRIPT_DEFAULT_SCRIPT_META environment variable.
+ * The environment variable should contain a JSON payload of PromptScript metadata.
+ * This metadata gets merged last into the main script metadata object.
+ *
+ * @param env - The environment variables as key-value pairs.
+ * @returns A PromptArgs object containing the parsed metadata, or undefined if no valid metadata found.
+ */
+export function parseDefaultMetaFromEnv(env: Record<string, string>): Partial<PromptArgs> | undefined {
+  const envValue = env.GENAISCRIPT_DEFAULT_SCRIPT_META;
+  if (!envValue) {
+    dbg("GENAISCRIPT_DEFAULT_SCRIPT_META not found in environment variables");
+    return undefined;
+  }
+
+  dbg(`found GENAISCRIPT_DEFAULT_SCRIPT_META: ${envValue}`);
+  
+  try {
+    const parsed = JSON5TryParse(envValue);
+    if (!parsed || typeof parsed !== "object") {
+      dbg("GENAISCRIPT_DEFAULT_SCRIPT_META could not be parsed as valid JSON object");
+      return undefined;
+    }
+
+    dbg(`parsed GENAISCRIPT_DEFAULT_SCRIPT_META: %O`, parsed);
+    
+    // Filter to only include valid PromptArgs fields (exclude text, id, jsSource, defTools, resolvedSystem)
+    const excludedFields = new Set(['text', 'id', 'jsSource', 'defTools', 'resolvedSystem']);
+    const filtered: Partial<PromptArgs> = {};
+    
+    for (const [key, value] of Object.entries(parsed)) {
+      if (!excludedFields.has(key)) {
+        (filtered as any)[key] = value;
+      }
+    }
+    
+    dbg(`filtered GENAISCRIPT_DEFAULT_SCRIPT_META: %O`, filtered);
+    return filtered;
+  } catch (error) {
+    dbg(`failed to parse GENAISCRIPT_DEFAULT_SCRIPT_META: ${error}`);
+    return undefined;
+  }
+}
+
 /**
  * Parses default configuration values from the provided environment variables.
  *
diff --git a/packages/core/src/template.ts b/packages/core/src/template.ts
index a3b174ddf5..98c763f846 100644
--- a/packages/core/src/template.ts
+++ b/packages/core/src/template.ts
@@ -15,6 +15,7 @@ import { deleteUndefinedValues } from "./cleaners.js";
 import { markdownScriptParse } from "./markdownscript.js";
 import { readJSON } from "./fs.js";
 import { frontmatterTryParse } from "./frontmatter.js";
+import { parseDefaultMetaFromEnv } from "./env.js";
 import type {
   PromptArgs,
   PromptScript,
@@ -241,5 +242,15 @@ export async function parsePromptScript(filename: string, content: string) {
     };
   }
 
+  // Parse and merge default metadata from environment variables (last to take priority)
+  const envDefaults = parseDefaultMetaFromEnv(process.env);
+  if (envDefaults?.metadata) {
+    // Only merge metadata field from environment defaults
+    script.metadata = metadataValidate({
+      ...(script.metadata || {}),
+      ...(envDefaults.metadata || {}), // env metadata takes precedence
+    });
+  }
+
   return script;
 }
diff --git a/packages/core/test/env.test.ts b/packages/core/test/env.test.ts
index 9c63bdc640..d5c0a9d065 100644
--- a/packages/core/test/env.test.ts
+++ b/packages/core/test/env.test.ts
@@ -1,5 +1,5 @@
 import { describe, test, assert } from "vitest";
-import { parseAllowedDomains } from "../src/env.js";
+import { parseAllowedDomains, parseDefaultMetaFromEnv } from "../src/env.js";
 
 describe("env", () => {
   describe("parseAllowedDomains", () => {
@@ -53,4 +53,83 @@ describe("env", () => {
       assert.deepStrictEqual(result, ["github.com"]);
     });
   });
+
+  describe("parseDefaultMetaFromEnv", () => {
+    test("returns undefined when GENAISCRIPT_DEFAULT_SCRIPT_META not set", () => {
+      const result = parseDefaultMetaFromEnv({});
+      assert.strictEqual(result, undefined);
+    });
+
+    test("parses valid JSON metadata", () => {
+      const env = {
+        GENAISCRIPT_DEFAULT_SCRIPT_META: '{"temperature": 0.5, "model": "gpt-4", "title": "Default Title"}'
+      };
+      const result = parseDefaultMetaFromEnv(env);
+      assert.deepStrictEqual(result, {
+        temperature: 0.5,
+        model: "gpt-4",
+        title: "Default Title"
+      });
+    });
+
+    test("parses valid JSON5 metadata", () => {
+      const env = {
+        GENAISCRIPT_DEFAULT_SCRIPT_META: '{temperature: 0.5, model: "gpt-4", unlisted: true}'
+      };
+      const result = parseDefaultMetaFromEnv(env);
+      assert.deepStrictEqual(result, {
+        temperature: 0.5,
+        model: "gpt-4",
+        unlisted: true
+      });
+    });
+
+    test("handles metadata with nested objects", () => {
+      const env = {
+        GENAISCRIPT_DEFAULT_SCRIPT_META: '{"metadata": {"key1": "value1", "key2": "value2"}, "vars": {"var1": "val1"}}'
+      };
+      const result = parseDefaultMetaFromEnv(env);
+      assert.deepStrictEqual(result, {
+        metadata: {
+          key1: "value1",
+          key2: "value2"
+        },
+        vars: {
+          var1: "val1"
+        }
+      });
+    });
+
+    test("returns undefined for invalid JSON", () => {
+      const env = {
+        GENAISCRIPT_DEFAULT_SCRIPT_META: 'invalid json {'
+      };
+      const result = parseDefaultMetaFromEnv(env);
+      assert.strictEqual(result, undefined);
+    });
+
+    test("returns undefined for non-object values", () => {
+      const env = {
+        GENAISCRIPT_DEFAULT_SCRIPT_META: '"just a string"'
+      };
+      const result = parseDefaultMetaFromEnv(env);
+      assert.strictEqual(result, undefined);
+    });
+
+    test("returns undefined for null values", () => {
+      const env = {
+        GENAISCRIPT_DEFAULT_SCRIPT_META: 'null'
+      };
+      const result = parseDefaultMetaFromEnv(env);
+      assert.strictEqual(result, undefined);
+    });
+
+    test("handles empty object", () => {
+      const env = {
+        GENAISCRIPT_DEFAULT_SCRIPT_META: '{}'
+      };
+      const result = parseDefaultMetaFromEnv(env);
+      assert.deepStrictEqual(result, {});
+    });
+  });
 });
\ No newline at end of file
diff --git a/packages/core/test/template.test.ts b/packages/core/test/template.test.ts
index 2fb581dfae..4345378be2 100644
--- a/packages/core/test/template.test.ts
+++ b/packages/core/test/template.test.ts
@@ -1,4 +1,4 @@
-import { describe, test, assert } from "vitest"
+import { describe, test, assert, vi, beforeEach, afterEach } from "vitest"
 import { parsePromptScript } from "../src/template.js"
 
 describe("template.ts - frontmatter parameters", () => {
@@ -119,4 +119,109 @@ Configuration test with {{items}} and {{config}}.`
             maximum: 1
         })
     })
+})
+
+describe("template.ts - environment variable default metadata", () => {
+    let originalEnv: any
+
+    beforeEach(() => {
+        originalEnv = { ...process.env }
+    })
+
+    afterEach(() => {
+        process.env = originalEnv
+    })
+
+    test("should merge environment default metadata into script metadata field", async () => {
+        process.env.GENAISCRIPT_DEFAULT_SCRIPT_META = '{"metadata": {"env_key": "env_value", "shared_key": "env_shared"}}'
+
+        const content = `script({
+            title: "Test Script",
+            description: "A test script",
+            metadata: {
+                script_key: "script_value",
+                shared_key: "script_shared"
+            }
+        })
+
+        Hello world!`
+
+        const script = await parsePromptScript("test.genai.mts", content)
+        
+        assert.strictEqual(script.title, "Test Script")
+        assert.strictEqual(script.description, "A test script")
+        assert.ok(script.metadata)
+        assert.strictEqual(script.metadata.env_key, "env_value")
+        assert.strictEqual(script.metadata.script_key, "script_value")
+        // Environment metadata should take precedence for shared keys
+        assert.strictEqual(script.metadata.shared_key, "env_shared")
+    })
+
+    test("should handle environment metadata without existing script metadata", async () => {
+        process.env.GENAISCRIPT_DEFAULT_SCRIPT_META = '{"metadata": {"env_key": "env_value"}}'
+
+        const content = `script({
+            title: "Test Script"
+        })
+
+        Hello world!`
+
+        const script = await parsePromptScript("test.genai.mts", content)
+        
+        assert.strictEqual(script.title, "Test Script")
+        assert.ok(script.metadata)
+        assert.strictEqual(script.metadata.env_key, "env_value")
+    })
+
+
+    test("should work without environment variable set", async () => {
+        delete process.env.GENAISCRIPT_DEFAULT_SCRIPT_META
+
+        const content = `script({
+            title: "Test Script",
+            metadata: {
+                original: "value"
+            }
+        })
+
+        Hello world!`
+
+        const script = await parsePromptScript("test.genai.mts", content)
+        
+        assert.strictEqual(script.title, "Test Script")
+        assert.ok(script.metadata)
+        assert.strictEqual(script.metadata.original, "value")
+    })
+
+    test("should handle invalid JSON in environment variable gracefully", async () => {
+        process.env.GENAISCRIPT_DEFAULT_SCRIPT_META = 'invalid json {'
+
+        const content = `script({
+            title: "Test Script"
+        })
+
+        Hello world!`
+
+        const script = await parsePromptScript("test.genai.mts", content)
+        
+        assert.strictEqual(script.title, "Test Script")
+        // Should not throw an error, just ignore the invalid env var
+    })
+
+    test("should handle environment metadata with nested objects", async () => {
+        process.env.GENAISCRIPT_DEFAULT_SCRIPT_META = '{"metadata": {"nested": {"key": "value"}, "simple": "data"}}'
+
+        const content = `script({
+            title: "Test Script"
+        })
+
+        Hello world!`
+
+        const script = await parsePromptScript("test.genai.mts", content)
+        
+        assert.strictEqual(script.title, "Test Script")
+        assert.ok(script.metadata)
+        assert.deepEqual(script.metadata.nested, { key: "value" })
+        assert.strictEqual(script.metadata.simple, "data")
+    })
 })
\ No newline at end of file