What causes "invalid format {format}" in neondatabase/neon?

Use ?format=pprof (default) or ?format=svg exactly, lowercase

neondatabase/neon · warning · ApiError

invalid format {format}

Error message

invalid format {format}

What it means

Returned as HTTP 400 BadRequest by profile_cpu_handler (the /profile/cpu debugging endpoint in neon's http-utils) when the optional format query parameter is present but is not one of the accepted values 'pprof' or 'svg'. The parameter is matched exactly (case-sensitive), and omitting it entirely is valid (defaults to pprof).

Source

Thrown at libs/http-utils/src/endpoint.rs:379

        }
    });

    Ok(response)
}

/// Generates CPU profiles.
pub async fn profile_cpu_handler(req: Request<Body>) -> Result<Response<Body>, ApiError> {
    enum Format {
        Pprof,
        Svg,
    }

    // Parameters.
    let format = match get_query_param(&req, "format")?.as_deref() {
        None => Format::Pprof,
        Some("pprof") => Format::Pprof,
        Some("svg") => Format::Svg,
        Some(format) => return Err(ApiError::BadRequest(anyhow!("invalid format {format}"))),
    };
    let seconds = match parse_query_param(&req, "seconds")? {
        None => 5,
        Some(seconds @ 1..=60) => seconds,
        Some(_) => return Err(ApiError::BadRequest(anyhow!("duration must be 1-60 secs"))),
    };
    let frequency_hz = match parse_query_param(&req, "frequency")? {
        None => 99,
        Some(1001..) => return Err(ApiError::BadRequest(anyhow!("frequency must be <=1000 Hz"))),
        Some(frequency) => frequency,
    };
    let force: bool = parse_query_param(&req, "force")?.unwrap_or_default();

    // Take the profile.
    static PROFILE_LOCK: Lazy<Mutex<()>> = Lazy::new(|| Mutex::new(()));
    static PROFILE_CANCEL: Lazy<Notify> = Lazy::new(Notify::new);

    let report = {

View on GitHub (pinned to 8f60b04da4)

Solutions

Use ?format=pprof (default) or ?format=svg exactly, lowercase
Omit the format parameter if the pprof protobuf output is acceptable
Check for URL-encoding mistakes that alter the value (e.g. svg%21)

Example fix

# before
curl 'http://localhost:9898/profile/cpu?format=flamegraph'   # 400 invalid format

# after
curl 'http://localhost:9898/profile/cpu?format=svg'

Defensive patterns

Strategy: validation

Validate before calling

# Validate before scraping:
format="${FORMAT:-pprof}"
[ "$format" = pprof ] || [ "$format" = svg ] || { echo "bad format"; exit 1; }
curl "http://localhost:9898/profile/cpu?format=$format"

Type guard

isPprofFormat(fmt) { return fmt === "pprof" || fmt === "svg"; }

Prevention

Pin scrape configs to the documented lowercase values
Default to omitting format when pprof is acceptable
Centralize endpoint URLs in one config to keep values consistent across tools

When it happens

Trigger: GET /profile/cpu?format=json, ?format=SVG, or ?format=pprof%2Bgzip — any format value other than exactly 'pprof' or 'svg' returns this 400.

Common situations: Grafana/pyroscope scrape config changed to request a new format; typo or uppercase value in the format param; tooling assuming flamegraph or json is supported.

Related errors

AI-assisted analysis of neondatabase/neon@8f60b04da4 (2026-08-16). Data as JSON: /api/errors/59f3964c352ebbd5. Report an issue: GitHub.