maturin "cargo metadata` exited with an error" in CI

By Kaveh Alemi·Latchkey

maturin runs cargo metadata to discover your crate before building. If Cargo cannot parse Cargo.toml, resolve dependencies, or find the manifest, that command exits non-zero and maturin reports the cargo metadata failure verbatim.

What this error means

The maturin build stops with "Cargo metadata failed" or "cargo metadata exited with an error", followed by the cargo error (a manifest parse error, an unresolved dependency, or a missing Cargo.toml).

💥 maturin failed
  Caused by: `cargo metadata` exited with an error: error: could not find `Cargo.toml`

Common causes

Cargo.toml is missing or in the wrong directory

maturin runs cargo from the manifest path; if Cargo.toml is absent at the expected location, cargo metadata fails immediately.

A dependency or workspace cannot be resolved

A bad version requirement, an unreachable registry, or a broken workspace member makes cargo metadata exit with an error.

How to fix it

Point maturin at the correct manifest

1. Confirm Cargo.toml exists at the project root or set manifest-path.
2. Run cargo metadata directly to see the real cargo error.
3. Fix the manifest or dependency cargo names.

cargo metadata --format-version 1
maturin build --manifest-path rust/Cargo.toml

Allow network access for dependency resolution

If the registry is unreachable on the runner, configure cargo to fetch deps or vendor them.

cargo fetch
maturin build --offline

How to prevent it

• Run cargo metadata in CI as a quick manifest sanity check.
• Keep Cargo.toml at the path maturin expects.
• Vendor or cache cargo dependencies for reliable resolution.

Frequently asked questions

Related guides

References

• Python documentation
• pip documentation
• GitHub Actions documentation