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
- Create a local Markdown file with the minimal content below.
- Open the file in Codex Desktop.
- Switch the file viewer to View preview / rich preview.
- 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/
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
.mdfileSteps to reproduce
Minimal Markdown
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 Reproductionline should continue to render as a heading.Actual behavior
---is rendered as a horizontal rule.---is rendered as another horizontal rule.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:
---linesA 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
HorizontalRulenodes 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:
<br>and missing images in Markdown preview.The current official release notes do not describe an intentional change to YAML frontmatter rendering:
https://openai.com/products/release-notes/