JSON Extract

Ask a modern VLM to return structured data and it will - wrapped in a JSON object nested three levels deep, possibly inside markdown fences, with the one field you actually need buried at $.result.items[0].value. JSON Extract is the pack's safe way to pull that field out without writing a regex or installing a scripting node.

It's part of the text toolkit in gokayfem's VLM_nodes pack - the dependency-free string/JSON utilities the pack ships so you can shape a model response without bolting on another custom-node pack. And "safe" is doing real work here: the implementation never evaluates code, follows references, or touches the filesystem. You give it JSON, it reads JSON.

How it works

You feed it text (plain or fenced JSON - it strips the fences for you), a path, and it resolves the path in one of two syntaxes:

• JSONPath-lite: $.result.items[0] - dot access with numeric indexes.
• RFC 6901 JSON Pointer: /result/items/0 - the standard pointer syntax.

It returns the value plus a found boolean and value_type (string, number, boolean, null, array, object...), and a canonical_json output with the cleaned-up document. output_format controls how the extracted value is rendered - Text for a plain value, or compact/pretty JSON when the value is itself a nested structure.

if_missing decides what happens when the path doesn't resolve: raise an error (the default), return an empty string, or return your default_value. For automation, the "Empty string" or "Default value" modes are usually the right call - a missing field shouldn't kill the whole queue.

Inputs and outputs

• text (STRING, multiline) - the JSON document (fences OK).
• path - $.dot[0] or /pointer syntax.
• output_format - Text / Compact JSON / Pretty JSON.
• if_missing / default_value - the missing-field policy.

Outputs: value, found, value_type, canonical_json.

Installing this pack

Same install as every node in this pack. ComfyUI Manager: search VLM_nodes. Or:

cd ComfyUI/custom_nodes
git clone https://github.com/gokayfem/ComfyUI_VLM_nodes
cd ComfyUI_VLM_nodes
python -m pip install -r requirements.txt

Run pip with ComfyUI's Python. This node has zero model downloads and no heavy deps - it's pure text handling.

Common issues

Path syntax is the classic stumble: $.items[0] uses a leading $, and JSON Pointer /items/0 starts with a slash and uses forward slashes, not dots - mixing the two gets you "path not found." If you're extracting from a VLM response that wrapped JSON in json ``` fences, no problem - it strips those. One more: keys with special characters like spaces or dots won't resolve cleanly in the JSONPath-lite syntax; the JSON Pointer form handles those better, which is why the node supports both.