Field [%s]: Bucket [%s] could not be converted to float64 in

Error message

Field [%s]: Bucket [%s] could not be converted to float64 in 'buckets' string [%s]

What it means

metrics.Init() parses the `buckets` tag for *Histogram fields by splitting on commas and calling strconv.ParseFloat(bucket, 64). An entry that is not a valid base-10 float triggers this error naming the field, the bucket, and the full buckets string.

Source

Thrown at internal/metrics/metrics.go:88

			switch {
			case field.Type.AssignableTo(timerPtrType):
				bucketValues := strings.Split(bucketString, ",")
				for _, bucket := range bucketValues {
					d, err := time.ParseDuration(bucket)
					if err != nil {
						return fmt.Errorf(
							"Field [%s]: Bucket [%s] could not be parsed as duration in 'buckets' string [%s]",
							field.Name, bucket, bucketString,
						)
					}
					timerBuckets = append(timerBuckets, d)
				}
			case field.Type.AssignableTo(histogramPtrType):
				bucketValues := strings.Split(bucketString, ",")
				for _, bucket := range bucketValues {
					b, err := strconv.ParseFloat(bucket, 64)
					if err != nil {
						return fmt.Errorf(
							"Field [%s]: Bucket [%s] could not be converted to float64 in 'buckets' string [%s]",
							field.Name, bucket, bucketString,
						)
					}
					histogramBuckets = append(histogramBuckets, b)
				}
			default:
				return fmt.Errorf(
					"Field [%s]: Buckets should only be defined for Timer and Histogram metric types",
					field.Name,
				)
			}
		}
		help := field.Tag.Get("help")
		var obj any
		switch {
		case field.Type.AssignableTo(counterPtrType):
			obj = factory.Counter(Options{

View on GitHub (pinned to 806f444784)

Solutions

Replace the offending entry with a valid float (e.g. '0.1', '1e3')
Remove duration units from histogram bucket values
Remove empty segments and stray commas
Check the field type: duration buckets belong on *Timer, floats on *Histogram

Example fix

// before
Size *Histogram `metric:"size" buckets:"1kb,10kb"`
// after
Size *Histogram `metric:"size" buckets:"1024,10240"`

Defensive patterns

Strategy: validation

Validate before calling

func checkHistogramBuckets(s string) error {
    for _, b := range strings.Split(s, ",") {
        if _, err := strconv.ParseFloat(b, 64); err != nil {
            return fmt.Errorf("bad float bucket %q", b)
        }
    }
    return nil
}

Try / catch

if err := metrics.Init(&m); err != nil {
    if strings.Contains(err.Error(), "could not be converted to float64") {
        // replace the non-numeric bucket on the named field
    }
    return err
}

Prevention

Histogram buckets must be plain floats — no units, no durations
Do not share bucket tag strings between Timer and Histogram fields
Strip commas/whitespace from entries
Precompute bucket strings like "0.001,0.01,0.1,1"

When it happens

Trigger: A *Histogram field with `buckets:"..."` containing a non-numeric entry, e.g. `buckets:"0.1,high,1.0"` or an empty segment from a trailing comma.

Common situations: Mixing up timer-style duration buckets with histogram float buckets; pasting duration strings like '10ms' into a histogram buckets tag; stray commas.

Related errors

AI-assisted analysis of jaegertracing/jaeger@806f444784 (2026-09-01). Data as JSON: /api/errors/3e2464c129da4cbe. Report an issue: GitHub.