tsenart/vegeta · error

bad buckets: %s

Error message

bad buckets: %s

What it means

vegeta's Buckets type (used by -buckets for histogram reporting) implements encoding.TextUnmarshaler and requires the literal format "[d1,d2,...]" — starting with '[' and ending with ']' and at least two characters. Any value not shaped like a bracketed list is rejected with this error before durations are parsed.

Source

Thrown at lib/histogram.go:69

		}
	}
	buf.WriteString("}")

	return buf.Bytes(), nil
}

// Nth returns the nth bucket represented as a string.
func (bs Buckets) Nth(i int) (left, right string) {
	if i >= len(bs)-1 {
		return bs[i].String(), "+Inf"
	}
	return bs[i].String(), bs[i+1].String()
}

// UnmarshalText implements the encoding.TextUnmarshaler interface.
func (bs *Buckets) UnmarshalText(value []byte) error {
	if len(value) < 2 || value[0] != '[' || value[len(value)-1] != ']' {
		return fmt.Errorf("bad buckets: %s", value)
	}
	for i, v := range strings.Split(string(value[1:len(value)-1]), ",") {
		d, err := time.ParseDuration(strings.TrimSpace(v))
		if err != nil {
			return err
		}
		// add a default range of [0-Buckets[0]) if needed
		if i == 0 && d > 0 {
			*bs = append(*bs, 0)
		}
		*bs = append(*bs, d)
	}
	if len(*bs) == 0 {
		return fmt.Errorf("bad buckets: %s", value)
	}
	return nil
}

View on GitHub (pinned to cf58112690)

Solutions

1. Wrap the durations in brackets: -buckets='[100ms,200ms,1s]'.
2. Quote the value in the shell so brackets are not glob-expanded or stripped.
3. Ensure the value has at least 2 characters (non-empty "[]").
4. After the format, verify each entry parses as a Go duration (100ms, 2s, 1m...).

Example fix

// before
vegeta report -buckets=100ms,200ms results.bin
// after
vegeta report -buckets='[100ms,200ms]' results.bin

func validBuckets(s string) bool {
	if len(s) < 2 || s[0] != '[' || s[len(s)-1] != ']' {
		return false
	}
	for _, v := range strings.Split(s[1:len(s)-1], ",") {
		if _, err := time.ParseDuration(strings.TrimSpace(v)); err != nil {
			return false
		}
	}
	return true
}

When it happens

Trigger: Calling Buckets.UnmarshalText (directly or via the -buckets flag's Set) with a value that is empty, a single character, or not wrapped in brackets — e.g. "100ms,200ms".

Common situations: Forgetting the surrounding brackets on the CLI; the shell eating the brackets (unquoted); passing a plain comma list copied from documentation prose.

Related errors

• -rate format %q doesn't match the "freq/duration" format (i.
• -max-body=%d overflows int64
• invalid -connect-to %q, expected format: %s
• -rate=0 requires setting -max-workers
• error opening %s: %s

AI-assisted analysis of tsenart/vegeta@cf58112690 (2026-08-31). Data as JSON: /api/errors/6f1327fbc1bc2ebe. Report an issue: GitHub.