caddyserver/caddy · error

quality too low; must be >= %d

Error message

quality too low; must be >= %d

What it means

Validate-time error from the gzip encoder: the configured compression Level is below gzip.StatelessCompression (-2), the lowest level Go's compress/gzip accepts.

Source

Thrown at modules/caddyhttp/encode/gzip/gzip.go:71

	if err != nil {
		return err
	}
	g.Level = level
	return nil
}

// Provision provisions g's configuration.
func (g *Gzip) Provision(ctx caddy.Context) error {
	if g.Level == 0 {
		g.Level = defaultGzipLevel
	}
	return nil
}

// Validate validates g's configuration.
func (g Gzip) Validate() error {
	if g.Level < gzip.StatelessCompression {
		return fmt.Errorf("quality too low; must be >= %d", gzip.StatelessCompression)
	}
	if g.Level > gzip.BestCompression {
		return fmt.Errorf("quality too high; must be <= %d", gzip.BestCompression)
	}
	return nil
}

// AcceptEncoding returns the name of the encoding as
// used in the Accept-Encoding request headers.
func (Gzip) AcceptEncoding() string { return "gzip" }

// NewEncoder returns a new gzip writer.
func (g Gzip) NewEncoder() encode.Encoder {
	writer, _ := gzip.NewWriterLevel(nil, g.Level)
	return writer
}

// Informed from http://blog.klauspost.com/gzip-performance-for-go-webservers/

View on GitHub (pinned to 50e54ee279)

Solutions

1. Set level within [-2, 9] (gzip.StatelessCompression..gzip.BestCompression); omit it to use the default
2. Remember gzip levels are not zstd's speed names — use numbers only

Example fix

// before
{"level": -3}
// after
{"level": 5}

// before applying config
if lvl < -2 || lvl > 9 { return fmt.Errorf("gzip level out of range: %d", lvl) }

When it happens

Trigger: {"level": -3} in the gzip encoder config, or a Caddyfile/JSON value that unmarshalates to a number < -2.

Common situations: Copy-pasting level values from other software (zstd/brotli use different ranges); negative numbers intended as 'no compression' set too low.

Related errors

• quality too high; must be <= %d
• encoding %s not enabled
• encoding %s is duplicated in prefer
• unexpected compression level, use one of '%s', '%s', '%s', '
• parsing listener address: %v

AI-assisted analysis of caddyserver/caddy@50e54ee279 (2026-08-15). Data as JSON: /api/errors/475cfe5a68011031. Report an issue: GitHub.