`pyproject.toml` is not a supported output format for `{}` (

Error message

`pyproject.toml` is not a supported output format for `{}` (only `requirements.txt`-style output is supported)

What it means

Error "`pyproject.toml` is not a supported output format for `{}` (only `requirements.txt`-style output is supported)" thrown in astral-sh/uv.

Source

Thrown at crates/uv/src/commands/pip/compile.rs:136

    annotation_style: AnnotationStyle,
    link_mode: LinkMode,
    mut python: Option<String>,
    system: bool,
    python_preference: PythonPreference,
    concurrency: Concurrency,
    quiet: bool,
    cache: Cache,
    workspace_cache: WorkspaceCache,
    printer: Printer,
    preview: Preview,
) -> Result<ExitStatus> {
    // If the user provides a `pyproject.toml` or other TOML file as the output file, raise an
    // error.
    if output_file
        .and_then(Path::file_name)
        .is_some_and(|name| name.eq_ignore_ascii_case("pyproject.toml"))
    {
        return Err(anyhow!(
            "`pyproject.toml` is not a supported output format for `{}` (only `requirements.txt`-style output is supported)",
            "uv pip compile".green()
        ));
    }

    // Determine the output format.
    let format = format.unwrap_or_else(|| {
        let extension = output_file.and_then(Path::extension);
        if extension.is_some_and(|ext| ext.eq_ignore_ascii_case("txt")) {
            PipCompileFormat::RequirementsTxt
        } else if extension.is_some_and(|ext| ext.eq_ignore_ascii_case("toml")) {
            PipCompileFormat::PylockToml
        } else {
            PipCompileFormat::RequirementsTxt
        }
    });

    // If the user is exporting to PEP 751, ensure the filename matches the specification.

View on GitHub (pinned to f1a42680ff)

When it happens

Trigger: Thrown at crates/uv/src/commands/pip/compile.rs:136 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of astral-sh/uv@f1a42680ff (2026-08-16). Data as JSON: /api/errors/32dc73562ad71790. Report an issue: GitHub.