How do I avoid leaving a partially written JSON configuration file?

Writing directly over the destination exposes a truncated file if the process crashes halfway through. Write a complete replacement before switching names. Create a temporary file in the destination directory, serialize and flush it, then use os.replace after successful writing. Where crash durability matters, consider file and directory synchronization appropriate to the operating system. Test an injected failure before replacement and verify the old file still parses. Atomic rename does not provide multi-writer coordination; concurrent writers can still overwrite one another. Preserve intended permissions, validate the new content and remove abandoned temporary files using a narrow cleanup policy.