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🔒 Quoting the Forge — Fixing YAML Frontmatter Parsing for Titles with Colons

🧩 The Problem

📝 Blog posts generated by the auto blog series pipeline include YAML frontmatter with titles, aliases, and metadata.

💥 Image generation started failing with a cryptic YAML parsing error: bad indentation of a mapping entry.

🔍 The failure only appeared when post titles contained colons, like The Silence After the Forge: Processing the Aftermath.

🔬 Root Cause

🔑 In YAML, a colon followed by a space is the key-value delimiter. When a title like My Blog: A Story appears unquoted in frontmatter, the YAML parser interprets A Story as a nested mapping value.

📄 The assembleFrontmatter function in blog-prompt.ts constructed frontmatter using a raw string template, inserting titles directly without quoting them.

🧱 Both the title and aliases fields were affected, producing invalid YAML that the js-yaml library correctly rejected during image generation.

🛠️ The Fix

✅ Introduced a quoteForYaml helper function that wraps values in double quotes and escapes any embedded backslashes or double-quote characters.

📐 The assembleFrontmatter function now builds a single displayTitle string and passes it through quoteForYaml for both the title and aliases YAML fields.

📝 The H1 heading below the frontmatter fence remains unquoted since it is plain Markdown, not YAML.

🧪 Verification

🧪 Added a dedicated test for titles with colons in the assembleFrontmatter test suite, confirming that the output YAML parses cleanly with js-yaml.

🖼️ Added a blog-image test that exercises updateFrontmatterFields on quoted frontmatter containing colons, verifying that the full image generation pipeline roundtrips correctly.

✅ All 1372 tests across both the scripts and quartz suites pass.

💡 Lessons Learned

🏗️ When constructing YAML by string interpolation, always quote string values that may contain special characters like colons, brackets, or hash marks.

🔄 A YAML dump library with forceQuotes enabled only protects the output path. If the input path also uses string interpolation, both sides need protection.

🔗 End-to-end testing that generates a post with a colon-rich title and then parses it for image generation would have caught this immediately.

📚 Book Recommendations

🔍 Similar

• YAML Ain’t Markup Language Specification by Oren Ben-Kiki, Clark Evans, and Ingy dot Net
• Crafting Interpreters by Robert Nystrom

🔄 Contrasting

• 💺🚪💡🤔 The Design of Everyday Things by Don Norman

🎨 Creatively Related

• Godel, Escher, Bach by Douglas Hofstadter

🦋 Bluesky

🔒 Quoting the Forge — Fixing YAML Frontmatter Parsing for Titles with Colons

AI Q: 💻 Ever crashed code because of a single misplaced character?

🧱 Data Structures | 📝 Text Processing | 🧪 Testing | 📚 Technical Books
https://bagrounds.org/ai-blog/2026-03-26-4-yaml-frontmatter-quoting-fix

— Bryan Grounds (@bagrounds.bsky.social) 2026-03-31T13:39:25.000Z

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