grafana/k6 · error

unexpected data after the JSON object

Error message

unexpected data after the JSON object

What it means

Raised by StrictJSONUnmarshal, k6's strict JSON decoding helper: after successfully decoding one JSON value there is trailing content in the input (e.g. two concatenated objects or stray tokens). It is a generic malformed-JSON guard used across options and config parsing.

Source

Thrown at lib/helpers.go:23

	"encoding/json"
	"fmt"
	"strings"
	"time"
)

// StrictJSONUnmarshal decodes a JSON in a strict manner, emitting an error if there
// are unknown fields or unexpected data
func StrictJSONUnmarshal(data []byte, v any) error {
	dec := json.NewDecoder(bytes.NewReader(data))
	dec.DisallowUnknownFields()
	dec.UseNumber()

	if err := dec.Decode(&v); err != nil {
		return err
	}
	if dec.More() {
		// TODO: use a custom error?
		return fmt.Errorf("unexpected data after the JSON object")
	}
	return nil
}

// GetMaxPlannedVUs returns the maximum number of planned VUs at any stage of
// the execution plan.
func GetMaxPlannedVUs(steps []ExecutionStep) (result uint64) {
	for _, s := range steps {
		stepMaxPlannedVUs := s.PlannedVUs
		if stepMaxPlannedVUs > result {
			result = stepMaxPlannedVUs
		}
	}
	return result
}

// GetMaxPossibleVUs returns the maximum number of planned + unplanned (i.e.
// initialized mid-test) VUs at any stage of the execution plan. Unplanned VUs

View on GitHub (pinned to 01ffac6f24)

Solutions

1. Ensure the configuration contains exactly one JSON object or array
2. Remove trailing commas, duplicate objects or stray characters after the main JSON
3. Validate the file with a JSON linter

When it happens

Trigger: Thrown at lib/helpers.go:23 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of grafana/k6@01ffac6f24 (2026-08-18). Data as JSON: /api/errors/fac45764e044e139. Report an issue: GitHub.