Field [%s]: Bucket [%s] could not be parsed as duration in '

Error message

Field [%s]: Bucket [%s] could not be parsed as duration in 'buckets' string [%s]

What it means

metrics.Init() parses the `buckets` tag for *Timer fields by splitting on commas and calling time.ParseDuration on each entry. Any bucket entry that is not a valid Go duration (e.g. '100' without a unit) causes this error naming the field, the bucket, and the whole buckets string.

Source

Thrown at internal/metrics/metrics.go:76

			for tagPair := range strings.SplitSeq(tagString, ",") {
				tag := strings.Split(tagPair, "=")
				if len(tag) != 2 {
					return fmt.Errorf(
						"Field [%s]: Tag [%s] is not of the form key=value in 'tags' string [%s]",
						field.Name, tagPair, tagString,
					)
				}
				tags[tag[0]] = tag[1]
			}
		}
		if bucketString := field.Tag.Get("buckets"); bucketString != "" {
			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)
				}

View on GitHub (pinned to 806f444784)

Solutions

Add a duration unit to the offending bucket (e.g. '50' -> '50ms')
Remove empty segments and stray commas from the buckets string
Use valid Go duration syntax: 1ms, 100ms, 1s, 2m
Validate the whole string with time.ParseDuration on each comma-separated part before running

Example fix

// before
Duration *Timer `metric:"dur" buckets:"1,10,100"`
// after
Duration *Timer `metric:"dur" buckets:"1ms,10ms,100ms"`

Defensive patterns

Strategy: validation

Validate before calling

func checkTimerBuckets(s string) error {
    for _, b := range strings.Split(s, ",") {
        if _, err := time.ParseDuration(b); err != nil {
            return fmt.Errorf("bad duration bucket %q", b)
        }
    }
    return nil
}

Try / catch

if err := metrics.Init(&m); err != nil {
    if strings.Contains(err.Error(), "could not be parsed as duration") {
        // fix the buckets string on the named field
    }
    return err
}

Prevention

Always include duration units (ms, s) in timer bucket values
Use Go duration literals identical to time.ParseDuration syntax
Avoid trailing commas in the buckets tag
Extract bucket lists into named constants reviewed once

When it happens

Trigger: A *Timer field with `buckets:"..."` containing an entry time.ParseDuration cannot parse, such as `buckets:"1ms,50,1s"` or `buckets:"10ms,"` (empty segment).

Common situations: Writing bare numbers for timer buckets forgetting duration units (ms, s); typos like '1ms ' with trailing space; trailing commas from copy-paste.

Related errors

AI-assisted analysis of jaegertracing/jaeger@806f444784 (2026-09-01). Data as JSON: /api/errors/2f948216b1021fcb. Report an issue: GitHub.