diff --git a/README.md b/README.md
index 46b5275..2bf71b4 100644
--- a/README.md
+++ b/README.md
@@ -119,6 +119,7 @@ Options:
 --respect-gitignore            skip files ignored by git
 --config <path>                path to debtlens.config.json
 --cwd <path>                   working directory
+--package <name>               scan a single npm workspace package (MVP: `packages/*` layouts)
 --no-color                     disable terminal color
 -q, --quiet                    terminal only: suppress per-finding detail
 --profile                      print per-rule timing to stderr without changing findings
diff --git a/docs/rule-packs.md b/docs/rule-packs.md
index 155fffa..1223b1e 100644
--- a/docs/rule-packs.md
+++ b/docs/rule-packs.md
@@ -62,7 +62,7 @@ separate rule IDs yet.
 | `next` | App Router boundaries, server/client splits, data loading | Planned |
 | `node` | Express/Fastify handlers, middleware depth, route sprawl | Planned |
 | `expo` | Expo config and module boundaries | Planned |
-| `monorepo` | Per-package configs, workspace-aware `--changed` | Planned ([#23](https://github.com/ColumbusLabs/DebtLens/issues/23)) |
+| `monorepo` | `--package` for single-level npm workspaces (`packages/*`); per-package configs planned | Partial ([#23](https://github.com/ColumbusLabs/DebtLens/issues/23)) |
 
 Vue and Svelte are planned JS framework packs. See [`ROADMAP.md`](../ROADMAP.md).
 
diff --git a/src/cli/index.ts b/src/cli/index.ts
index e5848d5..90bc200 100644
--- a/src/cli/index.ts
+++ b/src/cli/index.ts
@@ -5,6 +5,7 @@ import { Command } from "commander";
 import { loadConfig } from "../config/loadConfig.js";
 import { mergeConfig } from "../config/mergeConfig.js";
 import { listRulePacks, RULE_PACK_IDS } from "../config/packs.js";
+import { resolveWorkspacePackage } from "../config/workspaces.js";
 import { DEFAULT_BASELINE_FILENAME, applyBaseline, createBaseline, loadBaseline, writeBaseline } from "../core/baseline.js";
 import { scan } from "../core/scan.js";
 import { getChangedFiles, getRefSnapshot, getStagedFiles } from "../utils/git.js";
@@ -47,6 +48,7 @@ program.command("scan")
   .option("--respect-gitignore", "skip files ignored by git")
   .option("--config <path>", "path to debtlens.config.json")
   .option("--cwd <path>", "working directory", process.cwd())
+  .option("--package <name>", "scan a single workspace package by name")
   .option("--no-color", "disable ANSI color in terminal output")
   .option("-q, --quiet", "print only the summary line, suppress individual findings")
   .option("--profile", "print per-rule timing without changing findings")
@@ -83,7 +85,13 @@ program.command("scan")
         }
       }
 
-      const options = mergeConfig(target, fileConfig, {
+      let scanTarget = target;
+      if (rawOptions.package) {
+        const workspacePackage = resolveWorkspacePackage(cwd, String(rawOptions.package));
+        scanTarget = workspacePackage.directory;
+      }
+
+      const options = mergeConfig(scanTarget, fileConfig, {
         cwd,
         include: parseCommaList(rawOptions.include as string | undefined),
         exclude: parseCommaList(rawOptions.exclude as string | undefined),
diff --git a/src/config/workspaces.ts b/src/config/workspaces.ts
new file mode 100644
index 0000000..0a51896
--- /dev/null
+++ b/src/config/workspaces.ts
@@ -0,0 +1,83 @@
+import { existsSync, readFileSync } from "node:fs";
+import { dirname, resolve } from "node:path";
+import fg from "fast-glob";
+
+export interface WorkspacePackage {
+  name: string;
+  directory: string;
+}
+
+interface PackageJson {
+  name?: string;
+  workspaces?: string[] | { packages?: string[] };
+}
+
+/** Walk upward from cwd to find a package.json with a workspaces field. */
+export function findWorkspaceRoot(cwd: string): string | undefined {
+  let current = resolve(cwd);
+  while (true) {
+    const packageJsonPath = resolve(current, "package.json");
+    if (existsSync(packageJsonPath)) {
+      const parsed = JSON.parse(readFileSync(packageJsonPath, "utf8")) as PackageJson;
+      if (normalizeWorkspacePatterns(parsed.workspaces).length > 0) {
+        return current;
+      }
+    }
+    const parent = dirname(current);
+    if (parent === current) break;
+    current = parent;
+  }
+  return undefined;
+}
+
+export function listWorkspacePackages(workspaceRoot: string): WorkspacePackage[] {
+  const packageJsonPath = resolve(workspaceRoot, "package.json");
+  const parsed = JSON.parse(readFileSync(packageJsonPath, "utf8")) as PackageJson;
+  const patterns = normalizeWorkspacePatterns(parsed.workspaces);
+  const packages: WorkspacePackage[] = [];
+
+  for (const pattern of patterns) {
+    if (!pattern.endsWith("/*")) {
+      continue;
+    }
+    const directories = fg.sync(pattern, {
+      cwd: workspaceRoot,
+      onlyDirectories: true,
+      absolute: true,
+    });
+    for (const directory of directories) {
+      const childPath = resolve(directory, "package.json");
+      if (!existsSync(childPath)) continue;
+      const child = JSON.parse(readFileSync(childPath, "utf8")) as PackageJson;
+      if (!child.name) continue;
+      packages.push({ name: child.name, directory });
+    }
+  }
+
+  return packages.sort((left, right) => left.name.localeCompare(right.name));
+}
+
+export function resolveWorkspacePackage(
+  cwd: string,
+  packageName: string,
+): { workspaceRoot: string; directory: string } {
+  const workspaceRoot = findWorkspaceRoot(cwd);
+  if (!workspaceRoot) {
+    throw new Error("No npm/yarn/pnpm workspace found from the current directory.");
+  }
+
+  const packages = listWorkspacePackages(workspaceRoot);
+  const match = packages.find((pkg) => pkg.name === packageName);
+  if (!match) {
+    const available = packages.map((pkg) => pkg.name).join(", ");
+    throw new Error(`Workspace package "${packageName}" not found.${available ? ` Available: ${available}` : ""}`);
+  }
+
+  return { workspaceRoot, directory: match.directory };
+}
+
+function normalizeWorkspacePatterns(workspaces: PackageJson["workspaces"]): string[] {
+  if (!workspaces) return [];
+  if (Array.isArray(workspaces)) return workspaces;
+  return workspaces.packages ?? [];
+}
diff --git a/tests/fixtures/monorepo/monorepo.test.ts b/tests/fixtures/monorepo/monorepo.test.ts
new file mode 100644
index 0000000..8051a5a
--- /dev/null
+++ b/tests/fixtures/monorepo/monorepo.test.ts
@@ -0,0 +1,68 @@
+import assert from "node:assert/strict";
+import { execFileSync } from "node:child_process";
+import { spawnSync } from "node:child_process";
+import { dirname, join } from "node:path";
+import { fileURLToPath } from "node:url";
+import { describe, it } from "node:test";
+import { listWorkspacePackages, resolveWorkspacePackage } from "../../../src/config/workspaces.js";
+
+const repoRoot = join(dirname(fileURLToPath(import.meta.url)), "..", "..", "..");
+const fixtureRoot = join(dirname(fileURLToPath(import.meta.url)));
+const cliEntrypoint = join(repoRoot, "src", "cli", "index.ts");
+
+function runScan(args: string[]) {
+  return spawnSync(process.execPath, ["--import", "tsx", cliEntrypoint, "scan", ...args], {
+    cwd: repoRoot,
+    encoding: "utf8",
+  });
+}
+
+describe("workspace package resolution", () => {
+  it("lists workspace packages from a fixture monorepo", () => {
+    const packages = listWorkspacePackages(fixtureRoot);
+    assert.deepEqual(packages.map((pkg) => pkg.name), ["pkg-a", "pkg-b"]);
+  });
+
+  it("resolves a package directory by name", () => {
+    const resolved = resolveWorkspacePackage(fixtureRoot, "pkg-a");
+    assert.match(resolved.directory, /packages\/pkg-a$/);
+  });
+});
+
+describe("monorepo scan --package", () => {
+  it("scans only the selected workspace package", () => {
+    const result = runScan([
+      ".",
+      "--cwd",
+      fixtureRoot,
+      "--package",
+      "pkg-a",
+      "--rules",
+      "todo-comment",
+      "--format",
+      "json",
+    ]);
+    const parsed = JSON.parse(result.stdout);
+
+    assert.equal(result.status, 0);
+    assert.equal(parsed.summary.totalIssues, 1);
+    assert.match(parsed.issues[0].file, /^src\/index\.ts$/);
+  });
+
+  it("scans all workspace packages when --package is omitted", () => {
+    const result = runScan([
+      ".",
+      "--cwd",
+      fixtureRoot,
+      "--rules",
+      "todo-comment",
+      "--format",
+      "json",
+    ]);
+    const parsed = JSON.parse(result.stdout);
+
+    assert.equal(result.status, 0);
+    assert.equal(parsed.summary.totalIssues, 1);
+    assert.match(parsed.issues[0].file, /pkg-a/);
+  });
+});
diff --git a/tests/fixtures/monorepo/package.json b/tests/fixtures/monorepo/package.json
new file mode 100644
index 0000000..a47a3fc
--- /dev/null
+++ b/tests/fixtures/monorepo/package.json
@@ -0,0 +1,6 @@
+{
+  "name": "debtlens-fixture-monorepo",
+  "private": true,
+  "type": "module",
+  "workspaces": ["packages/*"]
+}
diff --git a/tests/fixtures/monorepo/packages/pkg-a/package.json b/tests/fixtures/monorepo/packages/pkg-a/package.json
new file mode 100644
index 0000000..b87254a
--- /dev/null
+++ b/tests/fixtures/monorepo/packages/pkg-a/package.json
@@ -0,0 +1,5 @@
+{
+  "name": "pkg-a",
+  "version": "1.0.0",
+  "private": true
+}
diff --git a/tests/fixtures/monorepo/packages/pkg-a/src/index.ts b/tests/fixtures/monorepo/packages/pkg-a/src/index.ts
new file mode 100644
index 0000000..e44a482
--- /dev/null
+++ b/tests/fixtures/monorepo/packages/pkg-a/src/index.ts
@@ -0,0 +1,2 @@
+// TODO: pkg-a only marker
+export const value = 1;
diff --git a/tests/fixtures/monorepo/packages/pkg-b/package.json b/tests/fixtures/monorepo/packages/pkg-b/package.json
new file mode 100644
index 0000000..f1b81ea
--- /dev/null
+++ b/tests/fixtures/monorepo/packages/pkg-b/package.json
@@ -0,0 +1,5 @@
+{
+  "name": "pkg-b",
+  "version": "1.0.0",
+  "private": true
+}
diff --git a/tests/fixtures/monorepo/packages/pkg-b/src/index.ts b/tests/fixtures/monorepo/packages/pkg-b/src/index.ts
new file mode 100644
index 0000000..44439d5
--- /dev/null
+++ b/tests/fixtures/monorepo/packages/pkg-b/src/index.ts
@@ -0,0 +1 @@
+export const value = 2;