kestra-io/kestra · error · PebbleException

The 'fromJson' function expects an argument 'json'.

Error message

The 'fromJson' function expects an argument 'json'.

What it means

Thrown by the 'fromJson' function when the args map does not contain the 'json' entry. 'json' is the single required argument (declared via getArgumentNames). A later branch returns null if json is present-but-null, and another checks the type, so this guard specifically covers a missing key.

Source

Thrown at core/src/main/java/io/kestra/core/runners/pebble/functions/FromJsonFunction.java:31

import io.pebbletemplates.pebble.template.PebbleTemplate;

public class FromJsonFunction implements KestraFunction {
    public static final String NAME = "fromJson";
    private static final ObjectMapper MAPPER = JacksonMapper.ofJson();

    public List<String> getArgumentNames() {
        return List.of("json");
    }

    @Override
    public Map<String, String> getArgumentDefaults() {
        return Map.of("json", ReadFileFunction.NAME + "('json/namespace/file')");
    }

    @Override
    public Object execute(Map<String, Object> args, PebbleTemplate self, EvaluationContext context, int lineNumber) {
        if (!args.containsKey("json")) {
            throw new PebbleException(null, "The 'fromJson' function expects an argument 'json'.", lineNumber, self.getName());
        }

        if (args.get("json") == null) {
            return null;
        }

        if (!(args.get("json") instanceof String)) {
            throw new PebbleException(null, "The 'fromJson' function expects an argument 'json' with type string.", lineNumber, self.getName());
        }

        String json = (String) args.get("json");
        ;

        try {
            return MAPPER.readValue(json, JacksonMapper.OBJECT_TYPE_REFERENCE);
        } catch (JsonProcessingException e) {
            throw new PebbleException(null, "Invalid json: " + e.getMessage(), lineNumber, self.getName());
        }

View on GitHub (pinned to 823fada927)

Solutions

1. Provide the 'json' argument, usually the output of readFile() on a JSON file: fromJson(readFile(outputs.fetch.body)).
2. If using named arguments, spell it exactly as 'json'.
3. Ensure the expression resolves to a JSON string, not a path or a parsed object.

Example fix

# before
obj: "{{ fromJson() }}"
# after
obj: "{{ fromJson(readFile('json/namespace/file')) }}"

# Ensure the 'json' argument is provided before calling fromJson().
# {{ (jsonContent != null) ? fromJson(jsonContent) : null }}

When it happens

Trigger: Calling fromJson() with no arguments, fromJson(other='x'), or misspelling the argument so Pebble does not bind it under 'json'.

Common situations: Forgetting the argument; assuming fromJson() takes a file path directly (it takes JSON content, typically via readFile()); copy-paste errors.

Related errors

• The 'fromJson' function expects an argument 'json' with type
• Invalid json: {e.getMessage()}
• The 'fromIon' function expects an argument 'ion'.
• Unable to transform to json value '{input}' with type '{inpu
• The 'encrypt' function expects two arguments 'key' and 'plai

AI-assisted analysis of kestra-io/kestra@823fada927 (2026-08-14). Data as JSON: /api/errors/7cc729460576113c. Report an issue: GitHub.