diff --git a/src/lib/utils.ts b/src/lib/utils.ts
index c35405dd5..993ed893f 100644
--- a/src/lib/utils.ts
+++ b/src/lib/utils.ts
@@ -25,15 +25,24 @@ export function isAllDigits(str: string): boolean {
  * Aligned with Sentry's canonical implementation:
  * https://github.com/getsentry/sentry/blob/master/static/app/utils/slugify.tsx
  *
- * @example slugify("My Cool App") // "my-cool-app"
- * @example slugify("my-app")      // "my-app"
- * @example slugify("Café Project") // "cafe-project"
- * @example slugify("my_app")      // "my_app"
+ * Diverges from Sentry's frontend canonical version in one place: `/` and `\`
+ * are normalized to a space before invalid-character stripping, so structural
+ * separators (npm scopes, monorepo path segments) become hyphens instead of
+ * being silently dropped. Without this, `@scope/pkg` would slugify to
+ * `scopepkg` instead of `scope-pkg`.
+ *
+ * @example slugify("My Cool App")    // "my-cool-app"
+ * @example slugify("my-app")         // "my-app"
+ * @example slugify("Café Project")   // "cafe-project"
+ * @example slugify("my_app")         // "my_app"
+ * @example slugify("@t3tools/web")   // "t3tools-web"
+ * @example slugify("packages/api")   // "packages-api"
  */
 export function slugify(name: string): string {
   return name
     .normalize("NFKD")
     .toLowerCase()
+    .replace(/[\\/]+/g, " ")
     .replace(/[^a-z0-9_\s-]/g, "")
     .replace(/[-\s]+/g, "-")
     .replace(/^-|-$/g, "");
diff --git a/test/lib/utils.property.test.ts b/test/lib/utils.property.test.ts
new file mode 100644
index 000000000..2dc04f0e4
--- /dev/null
+++ b/test/lib/utils.property.test.ts
@@ -0,0 +1,102 @@
+/**
+ * Property-Based Tests for src/lib/utils.ts
+ *
+ * Verifies invariants that should hold for any input to slugify, regardless
+ * of the characters present.
+ */
+
+import { describe, expect, test } from "bun:test";
+import {
+  array,
+  constantFrom,
+  assert as fcAssert,
+  property,
+  string,
+} from "fast-check";
+import { slugify } from "../../src/lib/utils.js";
+import { DEFAULT_NUM_RUNS } from "../model-based/helpers.js";
+
+/** Mix of valid slug chars, separators, scope/path glyphs, whitespace, and unicode */
+const messyChars =
+  "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789" +
+  "_-/\\@.: \tCaféñü漢";
+
+const messyInputArb = array(constantFrom(...messyChars.split("")), {
+  minLength: 0,
+  maxLength: 30,
+}).map((chars) => chars.join(""));
+
+const VALID_SLUG_RE = /^[a-z0-9_-]*$/;
+
+describe("property: slugify", () => {
+  test("output contains only [a-z0-9_-]", () => {
+    fcAssert(
+      property(messyInputArb, (input) => {
+        expect(slugify(input)).toMatch(VALID_SLUG_RE);
+      }),
+      { numRuns: DEFAULT_NUM_RUNS }
+    );
+  });
+
+  test("output never starts or ends with a hyphen", () => {
+    fcAssert(
+      property(messyInputArb, (input) => {
+        const out = slugify(input);
+        if (out.length > 0) {
+          expect(out.startsWith("-")).toBe(false);
+          expect(out.endsWith("-")).toBe(false);
+        }
+      }),
+      { numRuns: DEFAULT_NUM_RUNS }
+    );
+  });
+
+  test("output never contains consecutive hyphens", () => {
+    fcAssert(
+      property(messyInputArb, (input) => {
+        expect(slugify(input).includes("--")).toBe(false);
+      }),
+      { numRuns: DEFAULT_NUM_RUNS }
+    );
+  });
+
+  test("idempotent: slugify(slugify(x)) === slugify(x)", () => {
+    fcAssert(
+      property(messyInputArb, (input) => {
+        const once = slugify(input);
+        const twice = slugify(once);
+        expect(twice).toBe(once);
+      }),
+      { numRuns: DEFAULT_NUM_RUNS }
+    );
+  });
+
+  test("any arbitrary string still produces a valid slug", () => {
+    // Broader coverage with the unconstrained string arbitrary — catches
+    // anything the curated charset above might miss.
+    fcAssert(
+      property(string(), (input) => {
+        expect(slugify(input)).toMatch(VALID_SLUG_RE);
+      }),
+      { numRuns: DEFAULT_NUM_RUNS }
+    );
+  });
+
+  test("path/scope separators always become hyphens between alnum runs", () => {
+    // For inputs of the form "<a>/<b>" or "<a>\<b>" where both halves contain
+    // valid slug chars, the separator must produce a hyphen in the output —
+    // never a silent mash-up like "<a><b>".
+    const segmentChars = "abcdefghijklmnopqrstuvwxyz0123456789";
+    const segmentArb = array(constantFrom(...segmentChars.split("")), {
+      minLength: 1,
+      maxLength: 10,
+    }).map((chars) => chars.join(""));
+
+    fcAssert(
+      property(segmentArb, segmentArb, constantFrom("/", "\\"), (a, b, sep) => {
+        expect(slugify(`${a}${sep}${b}`)).toBe(`${a}-${b}`);
+      }),
+      { numRuns: DEFAULT_NUM_RUNS }
+    );
+  });
+});
diff --git a/test/lib/utils.test.ts b/test/lib/utils.test.ts
new file mode 100644
index 000000000..af9bd16bb
--- /dev/null
+++ b/test/lib/utils.test.ts
@@ -0,0 +1,113 @@
+/**
+ * Tests for src/lib/utils.ts
+ *
+ * Note: Core invariants (charset, idempotency, no leading/trailing/consecutive
+ * hyphens) are tested via property-based tests in utils.property.test.ts.
+ * These tests focus on specific inputs documented in JSDoc and regression
+ * cases for the npm-scope / monorepo path bug (CLI-1XX).
+ */
+
+import { describe, expect, test } from "bun:test";
+import { isAllDigits, slugify } from "../../src/lib/utils.js";
+
+describe("slugify", () => {
+  describe("JSDoc examples (canonical alignment)", () => {
+    test('slugify("My Cool App") → "my-cool-app"', () => {
+      expect(slugify("My Cool App")).toBe("my-cool-app");
+    });
+
+    test('slugify("my-app") → "my-app"', () => {
+      expect(slugify("my-app")).toBe("my-app");
+    });
+
+    test('slugify("Café Project") → "cafe-project"', () => {
+      expect(slugify("Café Project")).toBe("cafe-project");
+    });
+
+    test('slugify("my_app") → "my_app"', () => {
+      expect(slugify("my_app")).toBe("my_app");
+    });
+  });
+
+  describe("npm scoped package names", () => {
+    // Regression for the t3tools/web monorepo report — silently stripping
+    // `/` produced unreadable mashups like `t3toolsweb` instead of a useful
+    // `t3tools-web` slug.
+    test('slugify("@t3tools/web") → "t3tools-web"', () => {
+      expect(slugify("@t3tools/web")).toBe("t3tools-web");
+    });
+
+    test('slugify("@scope/pkg") → "scope-pkg"', () => {
+      expect(slugify("@scope/pkg")).toBe("scope-pkg");
+    });
+
+    test('slugify("@my-org/some-package") → "my-org-some-package"', () => {
+      expect(slugify("@my-org/some-package")).toBe("my-org-some-package");
+    });
+  });
+
+  describe("monorepo path-style names", () => {
+    test('slugify("packages/api") → "packages-api"', () => {
+      expect(slugify("packages/api")).toBe("packages-api");
+    });
+
+    test('slugify("apps/api/web") → "apps-api-web"', () => {
+      expect(slugify("apps/api/web")).toBe("apps-api-web");
+    });
+
+    test('slugify("apps\\\\api") → "apps-api"', () => {
+      expect(slugify("apps\\api")).toBe("apps-api");
+    });
+
+    test('slugify("@scope/My App") → "scope-my-app"', () => {
+      expect(slugify("@scope/My App")).toBe("scope-my-app");
+    });
+  });
+
+  describe("edge cases", () => {
+    test('slugify("") → ""', () => {
+      expect(slugify("")).toBe("");
+    });
+
+    test('slugify("///") → ""', () => {
+      expect(slugify("///")).toBe("");
+    });
+
+    test('slugify("@@@") → ""', () => {
+      expect(slugify("@@@")).toBe("");
+    });
+
+    test('slugify("@/foo") → "foo"', () => {
+      expect(slugify("@/foo")).toBe("foo");
+    });
+
+    test('slugify("///foo///") → "foo"', () => {
+      expect(slugify("///foo///")).toBe("foo");
+    });
+
+    test('slugify("---foo---") → "foo"', () => {
+      expect(slugify("---foo---")).toBe("foo");
+    });
+
+    test("collapses runs of slashes/spaces/hyphens", () => {
+      expect(slugify("foo // bar -- baz")).toBe("foo-bar-baz");
+    });
+  });
+});
+
+describe("isAllDigits", () => {
+  test("returns true for pure digits", () => {
+    expect(isAllDigits("0")).toBe(true);
+    expect(isAllDigits("123456")).toBe(true);
+  });
+
+  test("returns false for non-digit strings", () => {
+    expect(isAllDigits("PROJECT-ABC")).toBe(false);
+    expect(isAllDigits("abc123")).toBe(false);
+    expect(isAllDigits("123abc")).toBe(false);
+    expect(isAllDigits("")).toBe(false);
+    expect(isAllDigits("12.3")).toBe(false);
+    expect(isAllDigits("-1")).toBe(false);
+    expect(isAllDigits(" 123")).toBe(false);
+  });
+});