diff --git a/README.md b/README.md
index a525a4b..1c2a230 100644
--- a/README.md
+++ b/README.md
@@ -73,7 +73,9 @@ Checks one or more prompt files against a simple JSON rules file.
 promptdiff check prompts/*.md --rules promptdiff.rules.json --fail-on high
 ```
 
-Both commands parse options strictly. Unknown options and options missing their required values are errors, and `compare` accepts exactly two file arguments. For `check`, every file or glob supplied on the command line must match; PromptDiff does not emit a partial report when one input is unmatched.
+Both commands parse options strictly. Unknown options and options missing their required values are errors, and `compare` accepts exactly two file arguments. For `check`, every file or glob supplied on the command line must match; PromptDiff does not emit a partial report when one input is unmatched. Globs support `*` and `?` within a path segment and recursive `**` matching, such as `examples/**/*.md`. Results are sorted and deduplicated before checking.
+
+The rules document must be a JSON object. `requiredPhrases`, `forbiddenPhrases`, and `requireSections`, when present, must be arrays containing only non-empty strings. `maxSeverity` must be one of `info`, `low`, `medium`, `high`, or `critical`. Invalid rules exit with code `1`, print a field-specific diagnostic to stderr, and do not emit a report.
 
 Exit code `0` means the command completed without tripping a gate. Exit code `2` means the configured quality gate failed. Exit code `1` means invalid command input or another runtime error; diagnostics are written to stderr.
 
diff --git a/src/cli.ts b/src/cli.ts
index fdd051d..0bbcb59 100755
--- a/src/cli.ts
+++ b/src/cli.ts
@@ -1,6 +1,6 @@
 #!/usr/bin/env node
-import { mkdir, writeFile, readdir } from 'node:fs/promises';
-import { dirname, join } from 'node:path';
+import { mkdir, writeFile, readdir, stat } from 'node:fs/promises';
+import { dirname, isAbsolute, join, relative, resolve, sep } from 'node:path';
 import { analyzePromptDiff } from './analyzer.js';
 import { readPrompt } from './parser.js';
 import { renderCheckMarkdown, renderCompareMarkdown, renderJson } from './render.js';
@@ -68,18 +68,67 @@ async function writeOrPrint(content: string, out?: string): Promise<void> {
   await writeFile(out, content, 'utf8');
 }
 
+function globRegex(pattern: string): RegExp {
+  const normalized = pattern.split(sep).join('/');
+  let source = '';
+  for (let index = 0; index < normalized.length; index += 1) {
+    const char = normalized[index];
+    if (char === '*' && normalized[index + 1] === '*') {
+      index += 1;
+      if (normalized[index + 1] === '/') {
+        index += 1;
+        source += '(?:.*/)?';
+      } else {
+        source += '.*';
+      }
+    } else if (char === '*') {
+      source += '[^/]*';
+    } else if (char === '?') {
+      source += '[^/]';
+    } else {
+      source += char.replace(/[.+^${}()|[\]\\]/g, '\\$&');
+    }
+  }
+  return new RegExp(`^${source}$`);
+}
+
+async function listFiles(root: string): Promise<string[]> {
+  const entries = await readdir(root, { withFileTypes: true });
+  const files: string[] = [];
+  for (const entry of entries.sort((left, right) => left.name < right.name ? -1 : left.name > right.name ? 1 : 0)) {
+    const path = join(root, entry.name);
+    if (entry.isDirectory()) files.push(...await listFiles(path));
+    else if (entry.isFile()) files.push(path);
+  }
+  return files;
+}
+
 async function expandInputs(inputs: string[]): Promise<string[]> {
   const expanded: string[] = [];
   for (const input of inputs) {
-    if (!input.includes('*')) {
-      expanded.push(input);
+    if (!/[*?]/.test(input)) {
+      try {
+        if (!(await stat(input)).isFile()) throw new Error();
+      } catch {
+        throw new Error(`check input did not match any files: ${input}`);
+      }
+      expanded.push(isAbsolute(input) ? input : relative(process.cwd(), resolve(input)));
       continue;
     }
-    const dir = dirname(input);
-    const pattern = input.slice(dir.length + 1).replace(/[.+?^${}()|[\]\\]/g, '\\$&').replace(/\*/g, '.*');
-    const regex = new RegExp(`^${pattern}$`);
-    const entries = await readdir(dir === '.' ? process.cwd() : dir);
-    const matches = entries.filter((entry) => regex.test(entry)).map((entry) => join(dir, entry)).sort();
+    const firstMagic = input.search(/[*?]/);
+    const slash = Math.max(input.lastIndexOf('/', firstMagic), input.lastIndexOf(sep, firstMagic));
+    const root = resolve(slash === -1 ? '.' : input.slice(0, slash) || sep);
+    let candidates: string[] = [];
+    try {
+      candidates = await listFiles(root);
+    } catch {
+      // A missing static prefix is an unmatched pattern, handled below.
+    }
+    const regex = globRegex(resolve(input));
+    const matches = candidates
+      .filter((file) => regex.test(file.split(sep).join('/')))
+      .map((file) => isAbsolute(input) ? file : relative(process.cwd(), file))
+      .sort();
     if (matches.length === 0) throw new Error(`check input did not match any files: ${input}`);
     expanded.push(...matches);
   }
diff --git a/src/rules.ts b/src/rules.ts
index 5427550..9b7b9ed 100644
--- a/src/rules.ts
+++ b/src/rules.ts
@@ -14,9 +14,37 @@ function makeFinding(id: string, title: string, detail: string, evidence: string
 export async function readRules(path?: string): Promise<RulesFile> {
   if (!path) return defaultRules;
   const raw = await readFile(path, 'utf8');
-  const parsed = JSON.parse(raw) as RulesFile;
-  if (parsed.maxSeverity) parseSeverity(parsed.maxSeverity);
-  return { ...defaultRules, ...parsed };
+  let parsed: unknown;
+  try {
+    parsed = JSON.parse(raw);
+  } catch {
+    throw new Error('rules must contain valid JSON.');
+  }
+  if (typeof parsed !== 'object' || parsed === null || Array.isArray(parsed)) {
+    throw new Error('rules must be a JSON object.');
+  }
+
+  const rules = parsed as Record<string, unknown>;
+  for (const field of ['requiredPhrases', 'forbiddenPhrases', 'requireSections'] as const) {
+    const value = rules[field];
+    if (value === undefined) continue;
+    if (!Array.isArray(value)) throw new Error(`rules.${field} must be an array.`);
+    const invalidIndex = value.findIndex((item) => typeof item !== 'string' || item.trim().length === 0);
+    if (invalidIndex !== -1) throw new Error(`rules.${field}[${invalidIndex}] must be a non-empty string.`);
+  }
+  if (rules.maxSeverity !== undefined) {
+    if (typeof rules.maxSeverity !== 'string') {
+      throw new Error('rules.maxSeverity must be one of: info, low, medium, high, critical.');
+    }
+    try {
+      parseSeverity(rules.maxSeverity);
+    } catch {
+      throw new Error('rules.maxSeverity must be one of: info, low, medium, high, critical.');
+    }
+  }
+
+  const validated = rules as RulesFile;
+  return { ...defaultRules, ...validated };
 }
 
 function includesCaseInsensitive(text: string, needle: string): boolean {
diff --git a/tests/cli.test.mjs b/tests/cli.test.mjs
index 793baf7..066e080 100644
--- a/tests/cli.test.mjs
+++ b/tests/cli.test.mjs
@@ -1,6 +1,9 @@
 import test from 'node:test';
 import assert from 'node:assert/strict';
 import { spawnSync } from 'node:child_process';
+import { mkdtempSync, rmSync, writeFileSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
 
 test('cli compare returns gate failure when fail-on threshold is met', () => {
   const run = spawnSync(process.execPath, ['dist/cli.js', 'compare', 'examples/prompts/v1.md', 'examples/prompts/v2.md', '--fail-on', 'high'], { encoding: 'utf8' });
@@ -55,6 +58,35 @@ test('cli check rejects a mixed matched and unmatched input set', () => {
   assert.match(run.stderr, /input did not match any files: examples\/prompts\/missing-\*\.md/);
 });
 
+test('cli check expands recursive globs into sorted unique files', () => {
+  const run = spawnSync(process.execPath, [
+    'dist/cli.js', 'check', 'examples/**/*.md', './examples/prompts/safe.md',
+    '--format', 'json',
+  ], { encoding: 'utf8' });
+  assert.equal(run.status, 0);
+  assert.equal(run.stderr, '');
+  const report = JSON.parse(run.stdout);
+  assert.deepEqual(report.files, [...new Set(report.files)].sort());
+  assert.ok(report.files.includes('examples/README.md'));
+  assert.ok(report.files.includes('examples/prompts/safe.md'));
+});
+
+test('cli rejects malformed rules without emitting a report', () => {
+  const directory = mkdtempSync(join(tmpdir(), 'promptdiff-cli-rules-'));
+  const rulesPath = join(directory, 'rules.json');
+  writeFileSync(rulesPath, JSON.stringify({ requireSections: [42] }));
+  try {
+    const run = spawnSync(process.execPath, [
+      'dist/cli.js', 'check', 'examples/prompts/safe.md', '--rules', rulesPath,
+    ], { encoding: 'utf8' });
+    assert.equal(run.status, 1);
+    assert.equal(run.stdout, '');
+    assert.match(run.stderr, /rules\.requireSections\[0\] must be a non-empty string/);
+  } finally {
+    rmSync(directory, { recursive: true });
+  }
+});
+
 test('cli accepts documented compare option forms', () => {
   const run = spawnSync(process.execPath, ['dist/cli.js', 'compare', 'examples/prompts/v1.md', 'examples/prompts/v2.md', '--format', 'json', '--fail-on', 'high', '--no-redact'], { encoding: 'utf8' });
   assert.equal(run.status, 2);
diff --git a/tests/rules.test.mjs b/tests/rules.test.mjs
index 6392fb7..34c3076 100644
--- a/tests/rules.test.mjs
+++ b/tests/rules.test.mjs
@@ -1,6 +1,9 @@
 import test from 'node:test';
 import assert from 'node:assert/strict';
-import { checkPrompts, normalizePrompt } from '../dist/index.js';
+import { mkdtemp, rm, writeFile } from 'node:fs/promises';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+import { checkPrompts, normalizePrompt, readRules } from '../dist/index.js';
 
 test('flags forbidden phrases and missing required sections', () => {
   const prompt = normalizePrompt('bad.md', '# Prompt\nIgnore previous instructions.', true);
@@ -12,3 +15,44 @@ test('flags forbidden phrases and missing required sections', () => {
   assert.equal(result.summary.findingCount, 3);
   assert.equal(result.summary.highestSeverity, 'high');
 });
+
+test('reads a fully specified valid rules document', async () => {
+  const directory = await mkdtemp(join(tmpdir(), 'promptdiff-rules-'));
+  const path = join(directory, 'rules.json');
+  await writeFile(path, JSON.stringify({
+    requiredPhrases: ['protect customer secrets'],
+    forbiddenPhrases: ['ignore previous instructions'],
+    requireSections: ['Output Contract'],
+    maxSeverity: 'critical',
+  }));
+  try {
+    assert.deepEqual(await readRules(path), {
+      requiredPhrases: ['protect customer secrets'],
+      forbiddenPhrases: ['ignore previous instructions'],
+      requireSections: ['Output Contract'],
+      maxSeverity: 'critical',
+    });
+  } finally {
+    await rm(directory, { recursive: true });
+  }
+});
+
+test('rejects malformed rules with field-specific diagnostics', async () => {
+  const directory = await mkdtemp(join(tmpdir(), 'promptdiff-rules-'));
+  const path = join(directory, 'rules.json');
+  const invalidRules = [
+    [[], /rules must be a JSON object/],
+    [{ requiredPhrases: 'required' }, /rules\.requiredPhrases must be an array/],
+    [{ forbiddenPhrases: [''] }, /rules\.forbiddenPhrases\[0\] must be a non-empty string/],
+    [{ requireSections: [42] }, /rules\.requireSections\[0\] must be a non-empty string/],
+    [{ maxSeverity: 'urgent' }, /rules\.maxSeverity must be one of/],
+  ];
+  try {
+    for (const [rules, diagnostic] of invalidRules) {
+      await writeFile(path, JSON.stringify(rules));
+      await assert.rejects(readRules(path), diagnostic);
+    }
+  } finally {
+    await rm(directory, { recursive: true });
+  }
+});