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Codex Issues / #34440

Codex Desktop rich preview renders YAML frontmatter as body content

Resolved 💬 0 comments Opened Jul 21, 2026 by wibaekpark Closed Jul 21, 2026

Summary

When a local Markdown file with valid YAML frontmatter is opened in the integrated ChatGPT/Codex Desktop app and shown in rendered/rich preview, the frontmatter is no longer presented as document metadata.

Instead, the opening and closing --- delimiters are treated as Markdown horizontal rules, and the YAML key/value lines between them remain visible as ordinary body text. Markdown below the frontmatter (for example, a heading) is still rendered normally.

This appears to be a regression: the same workflow previously displayed the frontmatter using the metadata presentation.

Environment

  • ChatGPT/Codex Desktop: 26.715.31925 (build 5551)
  • macOS: 26.5.2 (25F84)
  • Architecture: Apple silicon / arm64
  • Codex CLI installed alongside the app: 0.142.5
  • File type: local .md file

Steps to reproduce

  1. Create a local Markdown file with the minimal content below.
  2. Open the file in Codex Desktop.
  3. Switch the file viewer to View preview / rich preview.
  4. Inspect the content at the top of the document.

Minimal Markdown

---
title: Frontmatter Preview Reproduction
description: Valid YAML frontmatter should render as document metadata.
tags: [codex, markdown, frontmatter]
timestamp: 2026-07-21T00:00:00+09:00
draft: false
---

# Frontmatter Preview Reproduction

This paragraph is ordinary Markdown body content.

Expected behavior

The leading YAML block should be recognized as frontmatter and rendered using the metadata/frontmatter presentation used by earlier Desktop builds. The raw --- delimiters and YAML source should not participate in normal Markdown body rendering.

The # Frontmatter Preview Reproduction line should continue to render as a heading.

Actual behavior

  • The opening --- is rendered as a horizontal rule.
  • The YAML properties are displayed as ordinary document text.
  • The closing --- is rendered as another horizontal rule.
  • The Markdown body below the block is otherwise rich-rendered normally.

Regression

This worked differently in earlier Codex Desktop builds: frontmatter was shown as metadata rather than as body syntax. The regression was observed on 26.715.31925; the exact last-known-good build is not available.

Validation / ruled-out file issues

The minimal file and representative affected documents were checked independently:

  • UTF-8, with no BOM
  • LF line endings
  • Opening delimiter at byte 0
  • Exact, unindented opening and closing --- lines
  • YAML parses successfully
  • No missing delimiter

A scan of the local Markdown corpus found 525 valid frontmatter documents and no BOM-prefixed frontmatter files. One unrelated document with an actual YAML error was excluded from testing.

Diagnostic clue

In the installed 26.715.31925 renderer bundle, Markdown source syntax highlighting has a frontmatter grammar, but the rich-preview editor extension list uses the normal Markdown parser without a frontmatter extension. The rich-preview decorations explicitly render HorizontalRule nodes as rules. This is consistent with the observed result: source view recognizes the YAML block, while rich preview interprets its delimiters as horizontal rules.

Duplicate check / adjacent issues

I searched the official issue tracker for frontmatter, YAML frontmatter, metadata, rich preview, and the horizontal-rule symptom and did not find this exact report.

Related but different issues:

The current official release notes do not describe an intentional change to YAML frontmatter rendering:
https://openai.com/products/release-notes/

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