What causes "Unable to parse jq value '{}' with type '{}'" in kestra-io/kestra?

If input is a String, ensure it parses as JSON (use `| json` or validate upstream).

kestra-io/kestra · error · PebbleException

Unable to parse jq value '{}' with type '{}'

Error message

Unable to parse jq value '{}' with type '{}'

What it means

Thrown by the 'jq' Pebble filter when either the jq expression fails to compile/apply or the input cannot be converted to a JsonNode. The filter wraps any exception from `JsonQuery.compile`, `JacksonMapper.ofJson().readTree(stringValue)` (for String input), `valueToTree(input)` (for other types), or the jq evaluation callback. The message echoes the raw input value and its Java class to aid diagnosis.

Source

Thrown at core/src/main/java/io/kestra/core/runners/pebble/filters/JqFilter.java:90

                    } else if (v instanceof NumericNode) {
                        out.add(v.numberValue());
                    } else if (v instanceof BooleanNode) {
                        out.add(v.booleanValue());
                    } else if (v instanceof ObjectNode) {
                        out.add(JacksonMapper.ofJson().convertValue(v, Map.class));
                    } else if (v instanceof ArrayNode) {
                        out.add(JacksonMapper.ofJson().convertValue(v, List.class));
                    } else {
                        out.add(v);
                    }
                });
            } catch (Exception e) {
                throw new Exception("Failed to resolve JQ expression '" + pattern + "' and value '" + input + "'", e);
            }

            return out;
        } catch (Exception e) {
            throw new PebbleException(e, "Unable to parse jq value '" + input + "' with type '" + input.getClass().getName() + "'", lineNumber, self.getName());
        }
    }
}

View on GitHub (pinned to 823fada927)

Solutions

If input is a String, ensure it parses as JSON (use `| json` or validate upstream).
Test the jq expression in an external jq 1.6 playground first.
If the input is already a Map/List, pass it directly rather than re-serializing to a String.
Read the wrapped cause in the stack trace for the exact jq/Jackson error.

Example fix

# before - string is not JSON
{{ outputs.api.body | jq(expression=".user.id") }}
# after - parse first
{% set parsed = outputs.api.body | json %}
{{ parsed | jq(expression=".user.id") }}

Defensive patterns

Strategy: validation

Validate before calling

# If input is a String, parse it to JSON first so jq receives a tree:
{% set parsed = (jsonString is string ? (jsonString | json) : jsonString) %}
{{ parsed | jq(expression=".id") }}

Type guard

# In a script task, verify Jackson can parse before exposing to the template:
# JsonNode node = JacksonMapper.ofJson().readTree(value);

Prevention

Always parse String inputs with the `json` filter before `jq`.
Validate jq expressions in a jq 1.6 playground (Kestra bundles 1.6 only).
Pass Maps/Lists directly to jq instead of re-serializing them.

When it happens

Trigger: Passing a String input that is not valid JSON (readTree throws); passing a malformed jq expression; passing an input whose type Jackson cannot serialize to a tree; a jq expression that triggers an error during evaluation (e.g. dividing by zero in jq, or applying an operator to an incompatible type).

Common situations: Feeding a plain text or XML body to `jq` instead of JSON; jq expression referencing a field that does not exist on a scalar; version mismatch between the jq syntax used and jq 1.6 (the only version Kestra bundles).

Understand the failure class

Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

AI-assisted analysis of kestra-io/kestra@823fada927 (2026-08-14). Data as JSON: /api/errors/e92657c660fbc649. Report an issue: GitHub.