Cargo "failed to parse manifest" - Fix Cargo.toml Errors in CI

Cargo could not read your Cargo.toml at all. The TOML is syntactically broken, names an unknown key, or has a malformed dependency entry -- the build stops before any resolution happens.

What this error means

cargo aborts immediately with error: failed to parse manifest at <path>/Cargo.toml followed by a Caused by: line pointing at the offending TOML. It is deterministic -- the same manifest fails the same way every run.

cargo

error: failed to parse manifest at `/home/runner/work/app/Cargo.toml`

Caused by:
  invalid type: string "1.0", expected a sequence
  in `dependencies.serde`

Common causes

Malformed TOML or wrong value type

A missing quote, a stray bracket, or giving a string where Cargo expects a table or array (for example serde = "1.0" written under a [dependencies.serde] table) makes the parse fail.

Unknown or misplaced manifest key

A typo in a section name ([dependancies]), a key under the wrong table, or a feature that needs a newer Cargo can all read as an invalid manifest.

How to fix it

Read the Caused-by line and fix that key

Look at the Caused by: message -- it names the exact field and the type mismatch.
Correct the offending entry: quote strings, close tables, and match the expected shape.
Run cargo verify-project to confirm the manifest parses before pushing.

Validate the manifest locally

cargo verify-project parses every manifest in the workspace and reports the first error.

Terminal

cargo verify-project
# or just:
cargo metadata --no-deps --format-version 1 >/dev/null

How to prevent it

Run cargo verify-project (or cargo metadata) in CI to catch manifest breakage early.
Use an editor with TOML validation so syntax errors surface before commit.
Keep dependency entries in their canonical shape (name = "x" or name = { ... }).