JSON Value Mutator

The name overpromises a little - this isn't a general JSON editing toolbox. What it is is the node you want when you've got a JSON object and need to add or overwrite exactly one key without hand-editing a giant string. For a workflow that builds request bodies or patches config on the fly, that single operation is genuinely useful.

How it works

Parse, patch, re-dump. The node takes input_json_string, loads it, and if you've supplied an append_key, sets that key:

input_json[append_key] = json.loads(append_value)

The subtle part is that it tries to parse append_value as JSON first. If the value is valid JSON - a number, a boolean, an array, a nested object - it's stored as that type, not as a string. If it fails to parse, the value is stored as a plain string. So "5" becomes the number 5, "true" becomes a boolean, "[1,2]" becomes an array, and "hello" stays "hello". That's a nice convenience and also the thing to watch: if you wanted the literal string "5", you'd need to quote it ('"5"'). If a key with the same name already exists, it's overwritten - hence "mutator."

Then it re-dumps the whole object with 4-space indent (pretty_enabled, default on) and optional key sorting.

Inputs and outputs

• input_json_string - the JSON object to modify, multiline.
• append_key - the key to add or overwrite.
• append_value - the value (parsed as JSON when possible).
• pretty_enabled, sort_enabled - output formatting toggles.

The output is Output JSON String. Invalid input JSON returns {"error": "Invalid JSON: ..."} instead of crashing.

Where it fits

The canonical use is building a request body for the pack's HttpRequestSender: start with a base JSON object, mutate in the one field that changes per run, and wire the result into body_json. It also works for updating a JSON config or inserting metadata before a save. One key per call is the limit - need two fields changed? Chain two of these. It's not a JSON Path editor and it won't reach into nested structures; it's a set-one-top-level-key tool, and it's good at exactly that.

Install

ComfyUI Manager → search "comfy-nekonote-extensions", or:

cd ComfyUI/custom_nodes
git clone https://github.com/0nyx-networks/comfy-nekonote-extensions

Restart ComfyUI; it's under NEKONOTE → Text. Part of the MIT-licensed comfy-nekonote-extensions utility pack by MINETA "m10i" Hiroki (v0.4.7) - zero models, and no dependencies beyond the Python standard library and what ComfyUI already ships. Written against the newer comfy_api.latest backend API, so a current ComfyUI is the one real requirement.