diff --git a/src/main.rs b/src/main.rs
index 2b9ebf5..c5e67c0 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -7,6 +7,7 @@ mod error;
 mod frame;
 mod lock;
 mod log;
+mod output;
 mod render;
 mod selection;
 
diff --git a/src/output.rs b/src/output.rs
new file mode 100644
index 0000000..7c82b3b
--- /dev/null
+++ b/src/output.rs
@@ -0,0 +1,231 @@
+use std::fmt::Write as _;
+use std::fs;
+use std::io::{Cursor, Write as _};
+use std::path::{Path, PathBuf};
+
+use anyhow::{Context, Result, anyhow};
+use chrono::{DateTime, Local};
+use image::{ImageFormat, RgbaImage};
+use wl_clipboard_rs::copy::{MimeType, Options, Source};
+
+use crate::error::HintExt;
+use crate::lock::Lock;
+
+/// Renders the strftime `template`. With `output`, appends ` (NAME)` before
+/// the extension, for `valw screen --all`.
+pub fn file_name(template: &str, now: &DateTime<Local>, output: Option<&str>) -> Result<String> {
+    let mut name = String::new();
+    write!(name, "{}", now.format(template))
+        .map_err(|_| anyhow!("invalid strftime pattern in save.filename: {template:?}"))
+        .hint("see https://docs.rs/chrono/latest/chrono/format/strftime for the syntax")?;
+    if name.is_empty() || name.contains('/') {
+        return Err(anyhow!(
+            "save.filename must render to a plain file name, got {name:?}"
+        ))
+        .hint("put folders in save.directory, not save.filename");
+    }
+    if let Some(output) = output {
+        name = with_suffix(&name, &format!(" ({output})"));
+    }
+    Ok(name)
+}
+
+/// Inserts `suffix` before the extension: `a.png` + ` (2)` = `a (2).png`.
+fn with_suffix(name: &str, suffix: &str) -> String {
+    match name.rsplit_once('.') {
+        Some((stem, ext)) if !stem.is_empty() => format!("{stem}{suffix}.{ext}"),
+        _ => format!("{name}{suffix}"),
+    }
+}
+
+/// `dir/name`, or `dir/name (2)`, `(3)`, … if taken.
+pub fn unique_path(dir: &Path, name: &str) -> PathBuf {
+    let first = dir.join(name);
+    if !first.exists() {
+        return first;
+    }
+    (2..)
+        .map(|n| dir.join(with_suffix(name, &format!(" ({n})"))))
+        .find(|p| !p.exists())
+        .expect("some suffix is free")
+}
+
+pub fn encode_png(img: &RgbaImage) -> Result<Vec<u8>> {
+    let mut png = Vec::new();
+    img.write_to(&mut Cursor::new(&mut png), ImageFormat::Png)
+        .context("could not encode PNG")?;
+    Ok(png)
+}
+
+/// Writes via a temp file in the same directory and a rename, so a partial
+/// screenshot never appears under the final name.
+pub fn write_atomic(path: &Path, bytes: &[u8]) -> Result<()> {
+    // "a.png" has the parent "", which means the current directory.
+    let dir = match path.parent() {
+        Some(p) if !p.as_os_str().is_empty() => p,
+        _ => Path::new("."),
+    };
+    fs::create_dir_all(dir)
+        .with_context(|| format!("could not create {}", dir.display()))
+        .hint("check save.directory in the config")?;
+    let name = path.file_name().context("path has no file name")?;
+    let tmp = dir.join(format!(".{}.tmp", name.to_string_lossy()));
+    let result = fs::write(&tmp, bytes).and_then(|()| fs::rename(&tmp, path));
+    if result.is_err() {
+        let _ = fs::remove_file(&tmp);
+    }
+    result.with_context(|| format!("could not write {}", path.display()))
+}
+
+pub fn write_stdout(bytes: &[u8]) -> Result<()> {
+    let mut out = std::io::stdout().lock();
+    out.write_all(bytes)
+        .and_then(|()| out.flush())
+        .context("could not write to stdout")
+}
+
+/// Copies `png` to the clipboard. The data is served by a forked child that
+/// lives until something else is copied, so this consumes the lock.
+pub fn copy_to_clipboard(png: Vec<u8>, lock: Lock) -> Result<()> {
+    let mut options = Options::new();
+    options.foreground(true);
+    let prepared = options
+        .prepare_copy(
+            Source::Bytes(png.into()),
+            MimeType::Specific("image/png".into()),
+        )
+        .context("could not copy to the clipboard")
+        .hint("the compositor needs ext-data-control or wlr-data-control; see `valw doctor`")?;
+    crate::detach::spawn(lock, move || {
+        let _ = prepared.serve();
+    })
+}
+
+/// Where a capture goes.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum Target {
+    /// Save under the config's directory and filename template.
+    Default,
+    /// `--output <path>`.
+    Path(PathBuf),
+    /// `--output -`.
+    Stdout,
+    /// `--clipboard-only`.
+    ClipboardOnly,
+}
+
+impl Target {
+    /// clap rejects `--output` together with `--clipboard-only`.
+    pub fn from_args(output: Option<PathBuf>, clipboard_only: bool) -> Target {
+        match output {
+            _ if clipboard_only => Target::ClipboardOnly,
+            Some(p) if p.as_os_str() == "-" => Target::Stdout,
+            Some(p) => Target::Path(p),
+            None => Target::Default,
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use chrono::TimeZone;
+
+    fn now() -> DateTime<Local> {
+        Local.with_ymd_and_hms(2026, 9, 29, 19, 4, 5).unwrap()
+    }
+
+    #[test]
+    fn default_template() {
+        let name = file_name("Screenshot %Y-%m-%d at %H.%M.%S.png", &now(), None).unwrap();
+        assert_eq!(name, "Screenshot 2026-09-29 at 19.04.05.png");
+    }
+
+    #[test]
+    fn output_suffix() {
+        let name = file_name("shot.png", &now(), Some("HDMI-A-1")).unwrap();
+        assert_eq!(name, "shot (HDMI-A-1).png");
+    }
+
+    #[test]
+    fn invalid_pattern_is_an_error_not_a_panic() {
+        let err = file_name("shot %Q.png", &now(), None).unwrap_err();
+        assert!(
+            format!("{err:#}").contains("invalid strftime pattern"),
+            "{err:#}"
+        );
+    }
+
+    #[test]
+    fn rejects_slashes_and_empty_names() {
+        assert!(file_name("%Y/%m.png", &now(), None).is_err());
+        assert!(file_name("", &now(), None).is_err());
+    }
+
+    #[test]
+    fn suffix_placement() {
+        assert_eq!(with_suffix("a.png", " (2)"), "a (2).png");
+        assert_eq!(with_suffix("a.b.png", " (2)"), "a.b (2).png");
+        assert_eq!(with_suffix("noext", " (2)"), "noext (2)");
+        assert_eq!(with_suffix(".hidden", " (2)"), ".hidden (2)");
+    }
+
+    #[test]
+    fn unique_path_counts_up() {
+        let dir = tempfile::tempdir().unwrap();
+        assert_eq!(unique_path(dir.path(), "a.png"), dir.path().join("a.png"));
+        fs::write(dir.path().join("a.png"), b"").unwrap();
+        fs::write(dir.path().join("a (2).png"), b"").unwrap();
+        assert_eq!(
+            unique_path(dir.path(), "a.png"),
+            dir.path().join("a (3).png")
+        );
+    }
+
+    #[test]
+    fn write_atomic_creates_dirs_and_leaves_no_temp() {
+        let dir = tempfile::tempdir().unwrap();
+        let path = dir.path().join("new/sub/a.png");
+        write_atomic(&path, b"png").unwrap();
+        assert_eq!(fs::read(&path).unwrap(), b"png");
+        let names: Vec<_> = fs::read_dir(path.parent().unwrap()).unwrap().collect();
+        assert_eq!(names.len(), 1);
+    }
+
+    #[test]
+    fn write_atomic_reports_unwritable_dir() {
+        let dir = tempfile::tempdir().unwrap();
+        let file = dir.path().join("file");
+        fs::write(&file, b"").unwrap();
+        let err = write_atomic(&file.join("a.png"), b"png").unwrap_err();
+        assert!(format!("{err:#}").contains("could not create"), "{err:#}");
+    }
+
+    #[test]
+    fn write_atomic_relative_path() {
+        let dir = tempfile::tempdir().unwrap();
+        std::env::set_current_dir(dir.path()).unwrap();
+        write_atomic(Path::new("a.png"), b"png").unwrap();
+        assert_eq!(fs::read(dir.path().join("a.png")).unwrap(), b"png");
+    }
+
+    #[test]
+    fn png_round_trip() {
+        let img = RgbaImage::from_raw(1, 1, vec![1, 2, 3, 255]).unwrap();
+        let png = encode_png(&img).unwrap();
+        let back = image::load_from_memory(&png).unwrap().to_rgba8();
+        assert_eq!(back, img);
+    }
+
+    #[test]
+    fn targets() {
+        use Target::*;
+        assert_eq!(Target::from_args(None, false), Default);
+        assert_eq!(Target::from_args(None, true), ClipboardOnly);
+        assert_eq!(Target::from_args(Some("-".into()), false), Stdout);
+        assert_eq!(
+            Target::from_args(Some("a.png".into()), false),
+            Path("a.png".into())
+        );
+    }
+}