diff --git a/Cargo.toml b/Cargo.toml
index 065e079..c6740d2 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -31,9 +31,14 @@ chrono = { version = "0.4.44", default-features = false, optional = true }
 dos-date-time = { version = "0.3.0", default-features = false, optional = true }
 jiff = { version = "0.2.24", default-features = false, optional = true }
 rand = { version = "0.10.1", default-features = false, optional = true }
-serde = { version = "1.0.228", default-features = false, features = ["derive"], optional = true }
 time = { version = "0.3.47", default-features = false }
 
+[dependencies.serde]
+version = "1.0.228"
+default-features = false
+features = ["derive"]
+optional = true
+
 [dev-dependencies]
 anyhow = "1.0.102"
 clap = { version = "4.6.1", features = ["derive"] }
diff --git a/tombi.toml b/tombi.toml
new file mode 100644
index 0000000..7df6d64
--- /dev/null
+++ b/tombi.toml
@@ -0,0 +1,6 @@
+# SPDX-FileCopyrightText: 2026 Shun Sakai
+#
+# SPDX-License-Identifier: Apache-2.0 OR MIT
+
+[format.rules]
+line-width = 80