What causes "manifest is missing either a `[package]` or a `[workspace]`" in rust-lang/cargo?

Add a [package] section with at minimum name, version, and edition to the manifest.

manifest is missing either a `[package]` or a `[workspace]`

Error message

manifest is missing either a `[package]` or a `[workspace]`

What it means

Thrown at the top level of manifest parsing after deserialization: if the TomlManifest has neither a [package] (nor [project]) section nor a [workspace] section, it is structurally invalid. Every Cargo.toml must define at least one of these. The error is wrapped with the file path via 'failed to parse manifest at ...'.

Solutions

Add a [package] section with at minimum name, version, and edition to the manifest.
If this is a virtual workspace root, add a [workspace] section with members = [...].
Verify you are pointing cargo at the correct file (not a config or lockfile).

Example fix

# before
[dependencies]
serde = "1.0"

# after
[package]
name = "my-crate"
version = "0.1.0"
edition = "2021"

[dependencies]
serde = "1.0"

Defensive patterns

Strategy: validation

Validate before calling

fn manifest_has_package_or_workspace(toml: &str) -> Result<(), String> {
    let parsed: toml::Value = toml::from_str(toml).map_err(|e| e.to_string())?;
    let has_pkg = parsed.get("package").is_some() || parsed.get("project").is_some();
    let has_ws = parsed.get("workspace").is_some();
    if !(has_pkg || has_ws) {
        return Err("manifest must contain [package] or [workspace]".into());
    }
    Ok(())
}

Type guard

fn is_valid_manifest_top_level(toml: &toml::Value) -> bool {
    toml.get("package").is_some() || toml.get("project").is_some() || toml.get("workspace").is_some()
}

Prevention

Ensure every Cargo.toml has a [package] or [workspace] header before running cargo.
Use project templates that always include a [package] section.
Validate generated manifests with `cargo metadata` in CI.

When it happens

Trigger: Calling the manifest parser on a Cargo.toml that contains only e.g. [dependencies] with no [package] or [workspace]. Also triggered by an empty file or a file with only a [lib]/[[bin]] target section.

Common situations: A developer creates a new Cargo.toml by hand and forgets the [package] header. A generated manifest template is incomplete. A file intended as a .cargo/config.toml is accidentally named Cargo.toml. A workspace root Cargo.toml missing the [workspace] table.

Related errors

AI-assisted analysis of rust-lang/cargo@98a09e7e7d (2026-08-11). Data as JSON: /api/errors/617f9edef4b6b245. Report an issue: GitHub.

Appendix: source

Thrown at src/workspace/parser/mod.rs:138

            .map(EitherManifest::Real)
        } else if normalized_toml.workspace.is_some() {
            assert!(!is_embedded);
            to_virtual_manifest(
                Some(contents),
                Some(document),
                original_toml,
                normalized_toml,
                features,
                workspace_config,
                source_id,
                path,
                gctx,
                &mut warnings,
                &mut errors,
            )
            .map(EitherManifest::Virtual)
        } else {
            anyhow::bail!("manifest is missing either a `[package]` or a `[workspace]`")
        }
    })()
    .map_err(|err| {
        ManifestError::new(
            err.context(format!("failed to parse manifest at `{}`", path.display())),
            path.into(),
        )
    })?;

    for warning in warnings {
        manifest.warnings_mut().add_warning(warning);
    }
    for error in errors {
        manifest.warnings_mut().add_critical_warning(error);
    }

    Ok(manifest)
}

View on GitHub (pinned to 98a09e7e7d)