diff --git a/package-lock.json b/package-lock.json
index 89ef280..4e5a169 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -29,7 +29,7 @@
         "vitest": "^4.0.18"
       },
       "engines": {
-        "node": ">=18"
+        "node": ">=20"
       }
     },
     "node_modules/@esbuild/aix-ppc64": {
diff --git a/src/tools/prompt-score.ts b/src/tools/prompt-score.ts
index 1cecf01..9e91532 100644
--- a/src/tools/prompt-score.ts
+++ b/src/tools/prompt-score.ts
@@ -40,7 +40,7 @@ interface ScoreResult {
   feedback: string[];
 }
 
-function scorePrompt(text: string): ScoreResult {
+export function scorePrompt(text: string): ScoreResult {
   const feedback: string[] = [];
   let specificity: number;
   let scope: number;
diff --git a/tests/tools/prompt-score.test.ts b/tests/tools/prompt-score.test.ts
new file mode 100644
index 0000000..1a8987b
--- /dev/null
+++ b/tests/tools/prompt-score.test.ts
@@ -0,0 +1,98 @@
+import { describe, it, expect } from "vitest";
+import { scorePrompt } from "../../src/tools/prompt-score.js";
+
+describe("scorePrompt", () => {
+  it("gives high specificity for file paths", () => {
+    const result = scorePrompt("Fix the bug in src/lib/config.ts where getConfig returns undefined");
+    expect(result.specificity).toBe(25);
+  });
+
+  it("gives high specificity for backtick identifiers", () => {
+    const result = scorePrompt("Rename `handleClick` to `onButtonPress`");
+    expect(result.specificity).toBe(25);
+  });
+
+  it("gives medium specificity for generic references", () => {
+    const result = scorePrompt("Update the component to use the new API");
+    expect(result.specificity).toBe(15);
+  });
+
+  it("gives low specificity for vague prompts", () => {
+    const result = scorePrompt("make it better");
+    expect(result.specificity).toBe(5);
+  });
+
+  it("gives high scope for bounded tasks", () => {
+    const result = scorePrompt("Only update the header color in the nav component");
+    expect(result.scope).toBe(25);
+  });
+
+  it("penalizes broad scope words", () => {
+    const result = scorePrompt("Refactor all the tests");
+    expect(result.scope).toBe(10);
+  });
+
+  it("gives high actionability for specific verbs", () => {
+    const result = scorePrompt("Extract the validation logic into a separate function");
+    expect(result.actionability).toBe(25);
+  });
+
+  it("gives medium actionability for vague verbs", () => {
+    const result = scorePrompt("Clean up the code");
+    expect(result.actionability).toBe(15);
+  });
+
+  it("gives low actionability for no verbs", () => {
+    const result = scorePrompt("the login page");
+    expect(result.actionability).toBe(5);
+  });
+
+  it("gives high done-condition for outcome words", () => {
+    const result = scorePrompt("Fix the function so it should return null on empty input");
+    expect(result.doneCondition).toBe(25);
+  });
+
+  it("gives medium done-condition for questions", () => {
+    const result = scorePrompt("Why is this failing?");
+    expect(result.doneCondition).toBe(20);
+  });
+
+  it("gives low done-condition when no outcome specified", () => {
+    const result = scorePrompt("refactor the code");
+    expect(result.doneCondition).toBe(5);
+  });
+
+  it("assigns correct letter grades", () => {
+    // High-quality prompt: specific file, bounded, action verb, outcome
+    const excellent = scorePrompt(
+      "Fix only the `parseDate` function in src/utils/date.ts so it should return null for invalid strings"
+    );
+    expect(excellent.total).toBeGreaterThanOrEqual(90);
+    expect(excellent.grade).toBe("A+");
+
+    // Terrible prompt
+    const bad = scorePrompt("stuff");
+    expect(bad.total).toBeLessThanOrEqual(30);
+    expect(bad.grade).toBe("F");
+  });
+
+  it("provides feedback for each low-scoring dimension", () => {
+    const result = scorePrompt("do stuff");
+    expect(result.feedback.length).toBeGreaterThan(0);
+    expect(result.feedback.some((f) => f.includes("📁"))).toBe(true); // specificity
+  });
+
+  it("congratulates on perfect prompts", () => {
+    const result = scorePrompt(
+      "Fix only the `parseDate` function in src/utils/date.ts so it should return null for invalid strings"
+    );
+    expect(result.feedback.some((f) => f.includes("🏆"))).toBe(true);
+  });
+
+  it("total equals sum of dimensions", () => {
+    const result = scorePrompt("Add a test for the login component");
+    expect(result.total).toBe(
+      result.specificity + result.scope + result.actionability + result.doneCondition
+    );
+  });
+});