diff --git a/README.md b/README.md
index 20e144d..17a2234 100644
--- a/README.md
+++ b/README.md
@@ -74,6 +74,14 @@ my-case/
 
 See [`fixtures/sample`](fixtures/sample) for working examples.
 
+When present, `meta.json` must contain a JSON object. `id`, `title`, and
+`notes` must be strings, while `tags` must be an array containing only strings.
+All fields may be omitted: the fixture directory name supplies `id` and
+`title`, with `[]` and an empty string used for `tags` and `notes`. Invalid
+metadata stops inspection with an error that names the fixture's `meta.json`
+file and the field that needs correction. Pipes and line breaks in these fields
+are escaped or normalized when Markdown reports are rendered.
+
 ## API
 
 ```js
diff --git a/src/fixtures.js b/src/fixtures.js
index d89adca..d28f69b 100644
--- a/src/fixtures.js
+++ b/src/fixtures.js
@@ -13,11 +13,13 @@ export async function discoverFixtures(rootDir) {
 }
 
 export async function loadFixture(dir) {
+  const metaPath = join(dir, 'meta.json');
   const [html, expected, meta] = await Promise.all([
     readFile(join(dir, 'input.html'), 'utf8'),
     readFile(join(dir, 'expected.txt'), 'utf8'),
-    readOptionalJson(join(dir, 'meta.json'))
+    readOptionalJson(metaPath)
   ]);
+  validateMetadata(meta, metaPath);
   return {
     id: meta.id ?? basename(dir),
     title: meta.title ?? basename(dir),
@@ -29,6 +31,20 @@ export async function loadFixture(dir) {
   };
 }
 
+function validateMetadata(meta, path) {
+  if (meta === null || typeof meta !== 'object' || Array.isArray(meta)) {
+    throw new Error(`${path}: fixture metadata must be a JSON object`);
+  }
+  for (const field of ['id', 'title', 'notes']) {
+    if (meta[field] !== undefined && typeof meta[field] !== 'string') {
+      throw new Error(`${path}: ${field} must be a string`);
+    }
+  }
+  if (meta.tags !== undefined && (!Array.isArray(meta.tags) || meta.tags.some((tag) => typeof tag !== 'string'))) {
+    throw new Error(`${path}: tags must be an array of strings`);
+  }
+}
+
 async function readOptionalJson(path) {
   try {
     return JSON.parse(await readFile(path, 'utf8'));
diff --git a/src/report.js b/src/report.js
index 3d6b19e..a7b2564 100644
--- a/src/report.js
+++ b/src/report.js
@@ -27,7 +27,7 @@ export function renderMarkdownReport(report) {
     '|---|---:|---|---|'
   ];
   for (const result of report.results) {
-    lines.push(`| ${result.id} | ${result.passed ? 'pass' : 'fail'} | ${result.tags.join(', ')} | ${result.notes.replace(/\|/g, '\\|')} |`);
+    lines.push(`| ${markdownCell(result.id)} | ${result.passed ? 'pass' : 'fail'} | ${markdownCell(result.tags.join(', '))} | ${markdownCell(result.notes)} |`);
   }
   for (const result of report.results.filter((item) => !item.passed)) {
     lines.push('', `## Diff: ${result.id}`, '', '```diff');
@@ -39,6 +39,10 @@ export function renderMarkdownReport(report) {
   return `${lines.join('\n')}\n`;
 }
 
+function markdownCell(value) {
+  return String(value).replace(/\r?\n|\r/g, '<br>').replace(/\|/g, '\\|');
+}
+
 export async function writeReport(report, outputDir) {
   await mkdir(outputDir, { recursive: true });
   const json = join(outputDir, 'plainforge-report.json');
diff --git a/test/fixtures.test.js b/test/fixtures.test.js
index 808738e..79c04e4 100644
--- a/test/fixtures.test.js
+++ b/test/fixtures.test.js
@@ -1,6 +1,9 @@
 import test from 'node:test';
 import assert from 'node:assert/strict';
-import { discoverFixtures, inspectFixtures } from '../src/index.js';
+import { mkdtemp, mkdir, rm, writeFile } from 'node:fs/promises';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+import { discoverFixtures, inspectFixtures, loadFixture } from '../src/index.js';
 
 test('discoverFixtures loads fixture metadata in stable order', async () => {
   const fixtures = await discoverFixtures('fixtures/sample');
@@ -13,3 +16,50 @@ test('inspectFixtures passes bundled sample fixtures', async () => {
   assert.equal(report.summary.total, 3);
   assert.equal(report.summary.failed, 0);
 });
+
+test('loadFixture preserves metadata defaults when meta.json or fields are omitted', async () => {
+  const root = await mkdtemp(join(tmpdir(), 'plainforge-fixture-'));
+  const fixtureDir = join(root, 'default-case');
+  try {
+    await mkdir(fixtureDir);
+    await writeFile(join(fixtureDir, 'input.html'), '<p>Expected</p>');
+    await writeFile(join(fixtureDir, 'expected.txt'), 'Expected');
+    assert.deepEqual(
+      (({ id, title, tags, notes }) => ({ id, title, tags, notes }))(await loadFixture(fixtureDir)),
+      { id: 'default-case', title: 'default-case', tags: [], notes: '' }
+    );
+    await writeFile(join(fixtureDir, 'meta.json'), '{}');
+    assert.equal((await loadFixture(fixtureDir)).id, 'default-case');
+  } finally {
+    await rm(root, { recursive: true, force: true });
+  }
+});
+
+test('loadFixture rejects malformed metadata with the metadata path', async () => {
+  const root = await mkdtemp(join(tmpdir(), 'plainforge-fixture-'));
+  const fixtureDir = join(root, 'invalid-case');
+  try {
+    await mkdir(fixtureDir);
+    await writeFile(join(fixtureDir, 'input.html'), '<p>Expected</p>');
+    await writeFile(join(fixtureDir, 'expected.txt'), 'Expected');
+    const invalidMetadata = [
+      ['null', 'fixture metadata must be a JSON object'],
+      ['[]', 'fixture metadata must be a JSON object'],
+      ['{"id":1}', 'id must be a string'],
+      ['{"title":false}', 'title must be a string'],
+      ['{"notes":{}}', 'notes must be a string'],
+      ['{"tags":"docs"}', 'tags must be an array of strings'],
+      ['{"tags":["docs",1]}', 'tags must be an array of strings']
+    ];
+    for (const [json, message] of invalidMetadata) {
+      await writeFile(join(fixtureDir, 'meta.json'), json);
+      await assert.rejects(loadFixture(fixtureDir), (error) => {
+        assert.match(error.message, /invalid-case\/meta\.json/);
+        assert.match(error.message, new RegExp(message));
+        return true;
+      });
+    }
+  } finally {
+    await rm(root, { recursive: true, force: true });
+  }
+});
diff --git a/test/report.test.js b/test/report.test.js
index f259ff0..43eb2a9 100644
--- a/test/report.test.js
+++ b/test/report.test.js
@@ -16,6 +16,15 @@ test('renderMarkdownReport summarizes results', () => {
   assert.match(markdown, /\| case \| pass \| x \| note \|/);
 });
 
+test('renderMarkdownReport escapes pipes and normalizes newlines in every user-controlled cell', () => {
+  const report = createReport([
+    { id: 'case|one\ncontinued', tags: ['docs|api', 'line\nbreak'], notes: 'first|line\r\nsecond', passed: true, diff: [] }
+  ], 'readable');
+  const markdown = renderMarkdownReport(report);
+  assert.match(markdown, /\| case\\\|one<br>continued \| pass \| docs\\\|api, line<br>break \| first\\\|line<br>second \|/);
+  assert.equal(markdown.split('\n').filter((line) => line.startsWith('| ')).length, 2);
+});
+
 test('writeReport writes json and markdown reports', async () => {
   const dir = await mkdtemp(join(tmpdir(), 'plainforge-'));
   try {