diff --git a/src/app.rs b/src/app.rs
index 9dfc86c..b00e1f9 100644
--- a/src/app.rs
+++ b/src/app.rs
@@ -88,7 +88,7 @@ impl App {
                 UnitAndTree::Blocks(reflection) => visualize!(reflection, ()),
             };
 
-            print!("{}", visualization); // it already ends with "\n", println! isn't needed here.
+            print!("{visualization}"); // it already ends with "\n", println! isn't needed here.
             return Ok(());
         }
 
diff --git a/src/app/sub.rs b/src/app/sub.rs
index 8fe17e3..e7739de 100644
--- a/src/app/sub.rs
+++ b/src/app/sub.rs
@@ -159,7 +159,7 @@ where
             max_depth,
         };
 
-        print!("{}", visualizer); // visualizer already ends with "\n", println! isn't needed here.
+        print!("{visualizer}"); // visualizer already ends with "\n", println! isn't needed here.
         Ok(())
     }
 }
diff --git a/src/lib.rs b/src/lib.rs
index fed11c1..75ddf64 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -16,7 +16,7 @@ pub mod runtime_error;
 #[cfg(feature = "cli")]
 pub fn main() -> std::process::ExitCode {
     if let Err(error) = app::App::from_env().run() {
-        eprintln!("[error] {}", error);
+        eprintln!("[error] {error}");
         return std::process::ExitCode::FAILURE;
     }
     std::process::ExitCode::SUCCESS
diff --git a/src/os_string_display.rs b/src/os_string_display.rs
index e7e33b8..e713aff 100644
--- a/src/os_string_display.rs
+++ b/src/os_string_display.rs
@@ -73,9 +73,9 @@ where
     fn fmt(&self, formatter: &mut Formatter<'_>) -> Result<(), Error> {
         let inner = self.as_os_str();
         if let Some(utf8) = inner.to_str() {
-            write!(formatter, "{}", utf8)
+            write!(formatter, "{utf8}")
         } else {
-            write!(formatter, "{:?}", inner)
+            write!(formatter, "{inner:?}")
         }
     }
 }
diff --git a/src/reporter/progress_report.rs b/src/reporter/progress_report.rs
index def67ba..e0466f8 100644
--- a/src/reporter/progress_report.rs
+++ b/src/reporter/progress_report.rs
@@ -29,7 +29,7 @@ impl<Size: size::Size + Into<u64>> ProgressReport<Size> {
         )
         .unwrap();
         if errors != 0 {
-            write!(text, ", erred {}", errors).unwrap();
+            write!(text, ", erred {errors}").unwrap();
         }
         write!(text, ")").unwrap();
         GLOBAL_STATUS_BOARD.temporary_message(&text);
diff --git a/src/status_board.rs b/src/status_board.rs
index eb72885..110a578 100644
--- a/src/status_board.rs
+++ b/src/status_board.rs
@@ -32,19 +32,19 @@ impl StatusBoard {
     /// Clear the line that the cursor is pointing to.
     pub fn clear_line(&self, new_line_width: usize) {
         let empty_line = repeat(' ', self.get_line_width());
-        eprint!("\r{}\r", empty_line);
+        eprint!("\r{empty_line}\r");
         self.set_line_width(new_line_width);
     }
 
     /// Show a temporary message.
     pub fn temporary_message(&self, message: &str) {
         self.clear_line(message.width());
-        eprint!("{}", message);
+        eprint!("{message}");
     }
 
     /// Log a permanent message.
     pub fn permanent_message(&self, message: &str) {
         self.clear_line(0);
-        eprintln!("{}", message);
+        eprintln!("{message}");
     }
 }
diff --git a/src/visualizer.rs b/src/visualizer.rs
index c5d6c7b..9db3395 100644
--- a/src/visualizer.rs
+++ b/src/visualizer.rs
@@ -40,7 +40,7 @@ use std::{fmt::Display, num::NonZeroUsize};
 ///     column_width_distribution: ColumnWidthDistribution::total(100),
 ///     max_depth: std::num::NonZeroUsize::new(10).unwrap(),
 /// };
-/// println!("{}", visualizer);
+/// println!("{visualizer}");
 /// # }
 /// ```
 #[derive(Debug)]
diff --git a/src/visualizer/display.rs b/src/visualizer/display.rs
index 389093c..1b3f513 100644
--- a/src/visualizer/display.rs
+++ b/src/visualizer/display.rs
@@ -9,7 +9,7 @@ where
 {
     /// Create the ASCII chart.
     fn fmt(&self, formatter: &mut Formatter<'_>) -> Result<(), Error> {
-        let write = |line: &String| writeln!(formatter, "{}", line);
+        let write = |line: &String| writeln!(formatter, "{line}");
         match self.direction {
             BottomUp => self.rows().iter().rev().try_for_each(write),
             TopDown => self.rows().iter().try_for_each(write),
diff --git a/src/visualizer/methods/initial_table.rs b/src/visualizer/methods/initial_table.rs
index 84c42fd..0a70482 100644
--- a/src/visualizer/methods/initial_table.rs
+++ b/src/visualizer/methods/initial_table.rs
@@ -120,7 +120,7 @@ where
                 "0%".to_string()
             } else {
                 let percentage = rounded_div::u64(fs_size * 100, total_fs_size);
-                format!("{}%", percentage)
+                format!("{percentage}%")
             };
             let size = node.size().display(visualizer.bytes_format).to_string();
             let sibling_count = ancestors.last().map_or(1, |parent| parent.children_count);
diff --git a/tests/_utils.rs b/tests/_utils.rs
index 6a56758..19bf6d6 100644
--- a/tests/_utils.rs
+++ b/tests/_utils.rs
@@ -58,7 +58,7 @@ impl Drop for Temp {
     fn drop(&mut self) {
         let path = &self.0;
         if let Err(error) = remove_dir_all(path) {
-            eprintln!("warning: Failed to delete {:?}: {}", path, error);
+            eprintln!("warning: Failed to delete {path:?}: {error}");
         }
     }
 }
@@ -133,7 +133,7 @@ where
     let suffix_size = |suffix: &str| -> Size {
         root.join(suffix)
             .pipe(metadata)
-            .unwrap_or_else(|error| panic!("get_size {}: {}", suffix, error))
+            .unwrap_or_else(|error| panic!("get_size {suffix}: {error}"))
             .pipe(|ref metadata| size_getter.get_size(metadata))
     };
 
@@ -327,6 +327,6 @@ pub fn inspect_stderr(stderr: &[u8]) {
     let text = String::from_utf8_lossy(stderr);
     let text = text.trim();
     if !text.is_empty() {
-        eprintln!("STDERR:\n{}\n", text);
+        eprintln!("STDERR:\n{text}\n");
     }
 }
diff --git a/tests/cli_errors.rs b/tests/cli_errors.rs
index 0c16604..35fd25a 100644
--- a/tests/cli_errors.rs
+++ b/tests/cli_errors.rs
@@ -62,7 +62,7 @@ fn min_ratio_1() {
     let stderr = String::from_utf8(stderr).expect("parse stderr as UTF-8");
     let stderr = stderr.trim_end();
     dbg!(&status);
-    eprintln!("STDERR:\n{}\n", stderr);
+    eprintln!("STDERR:\n{stderr}\n");
     assert!(!status.success());
     assert_eq!(
         stderr,
@@ -91,7 +91,7 @@ fn max_depth_0() {
     let stderr = String::from_utf8(stderr).expect("parse stderr as UTF-8");
     let stderr = stderr.trim_end();
     dbg!(&status);
-    eprintln!("STDERR:\n{}\n", stderr);
+    eprintln!("STDERR:\n{stderr}\n");
     assert!(!status.success());
     assert_eq!(
         stderr,
@@ -127,7 +127,7 @@ fn fs_errors() {
     let stderr = String::from_utf8(stderr).expect("parse stderr as UTF-8");
     let stdout = String::from_utf8(stdout).expect("parse stdout as UTF-8");
     dbg!(&status);
-    eprintln!("STDERR+STDOUT:\n{}{}\n", &stderr, &stdout);
+    eprintln!("STDERR+STDOUT:\n{stderr}{stdout}\n");
 
     let builder = FsTreeBuilder {
         root: workspace.to_path_buf(),
@@ -145,7 +145,7 @@ fn fs_errors() {
         column_width_distribution: ColumnWidthDistribution::total(100),
         max_depth: 10.try_into().unwrap(),
     };
-    let expected_stdout = format!("{}", visualizer);
+    let expected_stdout = format!("{visualizer}");
     eprintln!("EXPECTED STDOUT:\n{}\n", &expected_stdout);
 
     fs_permission(&workspace, "+rwx", true); // to allow SampleWorkspace destructor to clean itself
diff --git a/tests/json.rs b/tests/json.rs
index 29c3747..35a0a5e 100644
--- a/tests/json.rs
+++ b/tests/json.rs
@@ -101,7 +101,7 @@ fn json_input() {
         unit_and_tree: sample_tree().into_reflection().into(),
     };
     let json = serde_json::to_string_pretty(&json_data).expect("convert sample tree to JSON");
-    eprintln!("JSON: {}\n", json);
+    eprintln!("JSON: {json}\n");
     let workspace = Temp::new_dir().expect("create temporary directory");
     let mut child = Command::new(PDU)
         .with_current_dir(&workspace)
@@ -125,7 +125,7 @@ fn json_input() {
         .expect("wait for output of child process")
         .pipe(stdout_text);
     let actual = actual.trim_end();
-    eprintln!("ACTUAL:\n{}\n", &actual);
+    eprintln!("ACTUAL:\n{actual}\n");
 
     let visualizer = Visualizer {
         data_tree: &sample_tree(),
@@ -135,9 +135,9 @@ fn json_input() {
         column_width_distribution: ColumnWidthDistribution::total(100),
         max_depth: 10.try_into().unwrap(),
     };
-    let expected = format!("{}", visualizer);
+    let expected = format!("{visualizer}");
     let expected = expected.trim_end();
-    eprintln!("EXPECTED:\n{}\n", expected);
+    eprintln!("EXPECTED:\n{expected}\n");
 
     assert_eq!(actual, expected);
 }
@@ -173,7 +173,7 @@ fn json_output_json_input() {
         .output()
         .expect("spawn command with --json-input")
         .pipe(stdout_text);
-    eprintln!("ACTUAL:\n{}\n", &actual);
+    eprintln!("ACTUAL:\n{actual}\n");
 
     let expected = Command::new(PDU)
         .with_current_dir(&workspace)
@@ -188,7 +188,7 @@ fn json_output_json_input() {
         .output()
         .expect("spawn command for expected")
         .pipe(stdout_text);
-    eprintln!("EXPECTED:\n{}\n", expected);
+    eprintln!("EXPECTED:\n{expected}\n");
 
     assert_eq!(actual, expected);
 }
diff --git a/tests/usual_cli.rs b/tests/usual_cli.rs
index 71cf2ba..4cd6a26 100644
--- a/tests/usual_cli.rs
+++ b/tests/usual_cli.rs
@@ -37,7 +37,7 @@ fn total_width() {
         .output()
         .expect("spawn command")
         .pipe(stdout_text);
-    eprintln!("ACTUAL:\n{}\n", &actual);
+    eprintln!("ACTUAL:\n{actual}\n");
 
     let builder = FsTreeBuilder {
         root: workspace.to_path_buf(),
@@ -56,9 +56,9 @@ fn total_width() {
         column_width_distribution: ColumnWidthDistribution::total(100),
         max_depth: 10.try_into().unwrap(),
     };
-    let expected = format!("{}", visualizer);
+    let expected = format!("{visualizer}");
     let expected = expected.trim_end();
-    eprintln!("EXPECTED:\n{}\n", expected);
+    eprintln!("EXPECTED:\n{expected}\n");
 
     assert_eq!(actual, expected);
 }
@@ -75,7 +75,7 @@ fn column_width() {
         .output()
         .expect("spawn command")
         .pipe(stdout_text);
-    eprintln!("ACTUAL:\n{}\n", &actual);
+    eprintln!("ACTUAL:\n{actual}\n");
 
     let builder = FsTreeBuilder {
         root: workspace.to_path_buf(),
@@ -94,9 +94,9 @@ fn column_width() {
         column_width_distribution: ColumnWidthDistribution::components(10, 90),
         max_depth: 10.try_into().unwrap(),
     };
-    let expected = format!("{}", visualizer);
+    let expected = format!("{visualizer}");
     let expected = expected.trim_end();
-    eprintln!("EXPECTED:\n{}\n", expected);
+    eprintln!("EXPECTED:\n{expected}\n");
 
     assert_eq!(actual, expected);
 }
@@ -113,7 +113,7 @@ fn min_ratio_0() {
         .output()
         .expect("spawn command")
         .pipe(stdout_text);
-    eprintln!("ACTUAL:\n{}\n", &actual);
+    eprintln!("ACTUAL:\n{actual}\n");
 
     let builder = FsTreeBuilder {
         root: workspace.to_path_buf(),
@@ -131,9 +131,9 @@ fn min_ratio_0() {
         column_width_distribution: ColumnWidthDistribution::total(100),
         max_depth: 10.try_into().unwrap(),
     };
-    let expected = format!("{}", visualizer);
+    let expected = format!("{visualizer}");
     let expected = expected.trim_end();
-    eprintln!("EXPECTED:\n{}\n", expected);
+    eprintln!("EXPECTED:\n{expected}\n");
 
     assert_eq!(actual, expected);
 }
@@ -150,7 +150,7 @@ fn min_ratio() {
         .output()
         .expect("spawn command")
         .pipe(stdout_text);
-    eprintln!("ACTUAL:\n{}\n", &actual);
+    eprintln!("ACTUAL:\n{actual}\n");
 
     let builder = FsTreeBuilder {
         root: workspace.to_path_buf(),
@@ -169,9 +169,9 @@ fn min_ratio() {
         column_width_distribution: ColumnWidthDistribution::total(100),
         max_depth: 10.try_into().unwrap(),
     };
-    let expected = format!("{}", visualizer);
+    let expected = format!("{visualizer}");
     let expected = expected.trim_end();
-    eprintln!("EXPECTED:\n{}\n", expected);
+    eprintln!("EXPECTED:\n{expected}\n");
 
     assert_eq!(actual, expected);
 }
@@ -188,7 +188,7 @@ fn max_depth_2() {
         .output()
         .expect("spawn command")
         .pipe(stdout_text);
-    eprintln!("ACTUAL:\n{}\n", &actual);
+    eprintln!("ACTUAL:\n{actual}\n");
 
     let builder = FsTreeBuilder {
         root: workspace.to_path_buf(),
@@ -207,9 +207,9 @@ fn max_depth_2() {
         column_width_distribution: ColumnWidthDistribution::total(100),
         max_depth: 2.try_into().unwrap(),
     };
-    let expected = format!("{}", visualizer);
+    let expected = format!("{visualizer}");
     let expected = expected.trim_end();
-    eprintln!("EXPECTED:\n{}\n", expected);
+    eprintln!("EXPECTED:\n{expected}\n");
 
     assert_eq!(actual, expected);
 }
@@ -226,7 +226,7 @@ fn max_depth_1() {
         .output()
         .expect("spawn command")
         .pipe(stdout_text);
-    eprintln!("ACTUAL:\n{}\n", &actual);
+    eprintln!("ACTUAL:\n{actual}\n");
 
     let builder = FsTreeBuilder {
         root: workspace.to_path_buf(),
@@ -245,9 +245,9 @@ fn max_depth_1() {
         column_width_distribution: ColumnWidthDistribution::total(100),
         max_depth: 1.try_into().unwrap(),
     };
-    let expected = format!("{}", visualizer);
+    let expected = format!("{visualizer}");
     let expected = expected.trim_end();
-    eprintln!("EXPECTED:\n{}\n", expected);
+    eprintln!("EXPECTED:\n{expected}\n");
 
     assert_eq!(actual, expected);
 }
@@ -263,7 +263,7 @@ fn top_down() {
         .output()
         .expect("spawn command")
         .pipe(stdout_text);
-    eprintln!("ACTUAL:\n{}\n", &actual);
+    eprintln!("ACTUAL:\n{actual}\n");
 
     let builder = FsTreeBuilder {
         root: workspace.to_path_buf(),
@@ -282,9 +282,9 @@ fn top_down() {
         column_width_distribution: ColumnWidthDistribution::total(100),
         max_depth: 10.try_into().unwrap(),
     };
-    let expected = format!("{}", visualizer);
+    let expected = format!("{visualizer}");
     let expected = expected.trim_end();
-    eprintln!("EXPECTED:\n{}\n", expected);
+    eprintln!("EXPECTED:\n{expected}\n");
 
     assert_eq!(actual, expected);
 }
@@ -300,7 +300,7 @@ fn align_right() {
         .output()
         .expect("spawn command")
         .pipe(stdout_text);
-    eprintln!("ACTUAL:\n{}\n", &actual);
+    eprintln!("ACTUAL:\n{actual}\n");
 
     let builder = FsTreeBuilder {
         root: workspace.to_path_buf(),
@@ -319,9 +319,9 @@ fn align_right() {
         column_width_distribution: ColumnWidthDistribution::total(100),
         max_depth: 10.try_into().unwrap(),
     };
-    let expected = format!("{}", visualizer);
+    let expected = format!("{visualizer}");
     let expected = expected.trim_end();
-    eprintln!("EXPECTED:\n{}\n", expected);
+    eprintln!("EXPECTED:\n{expected}\n");
 
     assert_eq!(actual, expected);
 }
@@ -337,7 +337,7 @@ fn quantity_apparent_size() {
         .output()
         .expect("spawn command")
         .pipe(stdout_text);
-    eprintln!("ACTUAL:\n{}\n", &actual);
+    eprintln!("ACTUAL:\n{actual}\n");
 
     let builder = FsTreeBuilder {
         root: workspace.to_path_buf(),
@@ -356,9 +356,9 @@ fn quantity_apparent_size() {
         column_width_distribution: ColumnWidthDistribution::total(100),
         max_depth: 10.try_into().unwrap(),
     };
-    let expected = format!("{}", visualizer);
+    let expected = format!("{visualizer}");
     let expected = expected.trim_end();
-    eprintln!("EXPECTED:\n{}\n", expected);
+    eprintln!("EXPECTED:\n{expected}\n");
 
     assert_eq!(actual, expected);
 }
@@ -375,7 +375,7 @@ fn quantity_block_size() {
         .output()
         .expect("spawn command")
         .pipe(stdout_text);
-    eprintln!("ACTUAL:\n{}\n", &actual);
+    eprintln!("ACTUAL:\n{actual}\n");
 
     let builder = FsTreeBuilder {
         root: workspace.to_path_buf(),
@@ -394,9 +394,9 @@ fn quantity_block_size() {
         column_width_distribution: ColumnWidthDistribution::total(100),
         max_depth: 10.try_into().unwrap(),
     };
-    let expected = format!("{}", visualizer);
+    let expected = format!("{visualizer}");
     let expected = expected.trim_end();
-    eprintln!("EXPECTED:\n{}\n", expected);
+    eprintln!("EXPECTED:\n{expected}\n");
 
     assert_eq!(actual, expected);
 }
@@ -413,7 +413,7 @@ fn quantity_block_count() {
         .output()
         .expect("spawn command")
         .pipe(stdout_text);
-    eprintln!("ACTUAL:\n{}\n", &actual);
+    eprintln!("ACTUAL:\n{actual}\n");
 
     let builder = FsTreeBuilder {
         root: workspace.to_path_buf(),
@@ -432,9 +432,9 @@ fn quantity_block_count() {
         column_width_distribution: ColumnWidthDistribution::total(100),
         max_depth: 10.try_into().unwrap(),
     };
-    let expected = format!("{}", visualizer);
+    let expected = format!("{visualizer}");
     let expected = expected.trim_end();
-    eprintln!("EXPECTED:\n{}\n", expected);
+    eprintln!("EXPECTED:\n{expected}\n");
 
     assert_eq!(actual, expected);
 }
@@ -452,7 +452,7 @@ fn bytes_format_plain() {
         .output()
         .expect("spawn command")
         .pipe(stdout_text);
-    eprintln!("ACTUAL:\n{}\n", &actual);
+    eprintln!("ACTUAL:\n{actual}\n");
 
     let builder = FsTreeBuilder {
         root: workspace.to_path_buf(),
@@ -471,9 +471,9 @@ fn bytes_format_plain() {
         column_width_distribution: ColumnWidthDistribution::total(100),
         max_depth: 10.try_into().unwrap(),
     };
-    let expected = format!("{}", visualizer);
+    let expected = format!("{visualizer}");
     let expected = expected.trim_end();
-    eprintln!("EXPECTED:\n{}\n", expected);
+    eprintln!("EXPECTED:\n{expected}\n");
 
     assert_eq!(actual, expected);
 }
@@ -491,7 +491,7 @@ fn bytes_format_metric() {
         .output()
         .expect("spawn command")
         .pipe(stdout_text);
-    eprintln!("ACTUAL:\n{}\n", &actual);
+    eprintln!("ACTUAL:\n{actual}\n");
 
     let builder = FsTreeBuilder {
         root: workspace.to_path_buf(),
@@ -510,9 +510,9 @@ fn bytes_format_metric() {
         column_width_distribution: ColumnWidthDistribution::total(100),
         max_depth: 10.try_into().unwrap(),
     };
-    let expected = format!("{}", visualizer);
+    let expected = format!("{visualizer}");
     let expected = expected.trim_end();
-    eprintln!("EXPECTED:\n{}\n", expected);
+    eprintln!("EXPECTED:\n{expected}\n");
 
     assert_eq!(actual, expected);
 }
@@ -530,7 +530,7 @@ fn bytes_format_binary() {
         .output()
         .expect("spawn command")
         .pipe(stdout_text);
-    eprintln!("ACTUAL:\n{}\n", &actual);
+    eprintln!("ACTUAL:\n{actual}\n");
 
     let builder = FsTreeBuilder {
         root: workspace.to_path_buf(),
@@ -549,9 +549,9 @@ fn bytes_format_binary() {
         column_width_distribution: ColumnWidthDistribution::total(100),
         max_depth: 10.try_into().unwrap(),
     };
-    let expected = format!("{}", visualizer);
+    let expected = format!("{visualizer}");
     let expected = expected.trim_end();
-    eprintln!("EXPECTED:\n{}\n", expected);
+    eprintln!("EXPECTED:\n{expected}\n");
 
     assert_eq!(actual, expected);
 }
@@ -567,7 +567,7 @@ fn path_to_workspace() {
         .output()
         .expect("spawn command")
         .pipe(stdout_text);
-    eprintln!("ACTUAL:\n{}\n", &actual);
+    eprintln!("ACTUAL:\n{actual}\n");
 
     let builder = FsTreeBuilder {
         root: workspace.to_path_buf(),
@@ -585,9 +585,9 @@ fn path_to_workspace() {
         column_width_distribution: ColumnWidthDistribution::total(100),
         max_depth: 10.try_into().unwrap(),
     };
-    let expected = format!("{}", visualizer);
+    let expected = format!("{visualizer}");
     let expected = expected.trim_end();
-    eprintln!("EXPECTED:\n{}\n", expected);
+    eprintln!("EXPECTED:\n{expected}\n");
 
     assert_eq!(actual, expected);
 }
@@ -606,7 +606,7 @@ fn multiple_names() {
         .output()
         .expect("spawn command")
         .pipe(stdout_text);
-    eprintln!("ACTUAL:\n{}\n", &actual);
+    eprintln!("ACTUAL:\n{actual}\n");
 
     let mut data_tree = ["nested", "flat", "empty-dir"]
         .iter()
@@ -637,9 +637,9 @@ fn multiple_names() {
         column_width_distribution: ColumnWidthDistribution::total(100),
         max_depth: 10.try_into().unwrap(),
     };
-    let expected = format!("{}", visualizer);
+    let expected = format!("{visualizer}");
     let expected = expected.trim_end();
-    eprintln!("EXPECTED:\n{}\n", expected);
+    eprintln!("EXPECTED:\n{expected}\n");
 
     assert_eq!(actual, expected);
 }
diff --git a/tests/visualizer.rs b/tests/visualizer.rs
index 936f1e3..e693f28 100644
--- a/tests/visualizer.rs
+++ b/tests/visualizer.rs
@@ -47,7 +47,7 @@ macro_rules! test_case {
             }
             .to_string();
             let expected = $expected;
-            eprintln!("\nACTUAL:\n{}\n", &actual);
+            eprintln!("\nACTUAL:\n{actual}\n");
 
             let actual_lines: Vec<_> = actual.lines().collect();
             let expected_lines: Vec<_> = expected.lines().collect();