Light-Tool: Serialize a JSON object

ComfyUI's data world is full of things that are secretly JSON - API responses, configs, metadata - and a lot of your other nodes only speak in strings. This node is the translator in one direction: it takes a JSON object and serializes it into a compact JSON string. That's the whole job, and it's the missing adapter whenever you have a dict on one end of a wire and a text node on the other.

What it does

One input, json_object, typed as a wildcard (*) so it accepts a dict/object from any node that emits one. One output, json_str. The mechanism is just json.dumps with ensure_ascii=False, which means non-ASCII characters (accents, CJK, emoji) survive intact rather than being escaped to \uXXXX sequences - a genuinely thoughtful touch, and relevant since this pack's author works in Chinese as well as English. If serialization somehow fails, it returns {} rather than crashing your graph.

The natural companion is the pack's own Deserialize Json String node (the reverse direction) and its KeyValue node (which pulls a value out of a JSON string by dot-notation path). Put together: object → serialize → string → keyvalue or into text nodes, or object → string → deserialize → object. That round-trip pair is the pack's complete JSON toolkit.

Why you'd actually use it

Three jobs. Metadata plumbing: this pack's Save Metadata node wants a JSON string of tags to embed in a PNG - this is the node that produces one from structured data. Prompt/config assembly: when a node outputs a structured object you want to splice into a prompt or a log line, serialize it first. Saving structured data to text: any time a dict needs to ride a text wire (to be written to a file, shown in Show Text, or passed to an API), this is the bridge.

It's a boring, correct, dependency-free adapter - the kind of node that makes a wildcard-heavy graph actually work instead of ending in a type error.

Installing it

Part of ComfyUI-Light-Tool by Hmily. ComfyUI Manager → search "ComfyUI-Light-Tool" → Install → restart, or:

cd ComfyUI/custom_nodes
git clone https://github.com/ihmily/ComfyUI-Light-Tool
pip install -r requirements.txt
# restart ComfyUI

Pure Python's stdlib json module - no models, no keys, offline.

Where people get burned

• The output is a single-line string. json.dumps here doesn't indent, so your pretty multi-line JSON becomes one long line. Fine for plumbing, awkward for eyeballing - run it through Show Text if you want to inspect it, or pretty-print with Show Anything first.
• Wildcard input, string output. The input type is loose (*) but the output is a real string. Don't feed the result into a node expecting a dict - that's what Deserialize is for.
• {} on failure. A silently-empty result beats a crash, but it also means a broken upstream can hide. Check your object source.

Small, fast, and exactly what it says on the tin. When your graph stops complaining about types, this is often why.