Nice one. Mermaid validation is a huge issue given how mermaid.js is architected.
I built a mermaid generation harness last year and even the best model at it (Claude Sonnet 3.7 at the time; 4o was okay, Gemini struggled) only produced valid mermaid ~95% of the time. That failure rate adds up quickly. Had to detect errors client-side and trigger retries to keep server load reasonable.
Having a lightweight parser with auto-fix like this back then would have simplified the flow quite a bit.
I built a mermaid generation harness last year and even the best model at it (Claude Sonnet 3.7 at the time; 4o was okay, Gemini struggled) only produced valid mermaid ~95% of the time. That failure rate adds up quickly. Had to detect errors client-side and trigger retries to keep server load reasonable.
Having a lightweight parser with auto-fix like this back then would have simplified the flow quite a bit.