diff --git a/rust/src/fmt.rs b/rust/src/fmt.rs
new file mode 100644
index 0000000..4a5f778
--- /dev/null
+++ b/rust/src/fmt.rs
@@ -0,0 +1,73 @@
+//! Formatting helpers, byte-for-byte parity with `tokenline.sh`.
+//!
+//! This slice carries `fmt_k` / `fmt_eta`; the 256-color palette and the
+//! ISO-8601 → epoch parser land in the next two slices.
+
+/// Compact token count, mirroring the bash `fmt_k` (awk `%.1f`):
+/// `1_500_000 -> "1.5M"`, `25_600 -> "25.6k"`, `900 -> "900"`.
+pub fn fmt_k(v: u64) -> String {
+    if v >= 1_000_000 {
+        format!("{:.1}M", v as f64 / 1_000_000.0)
+    } else if v >= 1_000 {
+        format!("{:.1}k", v as f64 / 1_000.0)
+    } else {
+        v.to_string()
+    }
+}
+
+/// Human ETA from raw seconds, mirroring the bash `fmt_eta`:
+/// `<=0 -> "now"`, `<1h -> "%dm"`, `<1d -> "%dh%dm"/"%dh"`, else `"%dd%dh"/"%dd"`.
+pub fn fmt_eta(secs: i64) -> String {
+    if secs <= 0 {
+        return "now".to_string();
+    }
+    if secs < 3600 {
+        return format!("{}m", secs / 60);
+    }
+    if secs < 86_400 {
+        let (h, m) = (secs / 3600, (secs % 3600) / 60);
+        return if m > 0 {
+            format!("{}h{}m", h, m)
+        } else {
+            format!("{}h", h)
+        };
+    }
+    let (d, h) = (secs / 86_400, (secs % 86_400) / 3600);
+    if h > 0 {
+        format!("{}d{}h", d, h)
+    } else {
+        format!("{}d", d)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn fmt_k_tiers() {
+        assert_eq!(fmt_k(0), "0");
+        assert_eq!(fmt_k(900), "900");
+        assert_eq!(fmt_k(999), "999");
+        assert_eq!(fmt_k(1_000), "1.0k");
+        assert_eq!(fmt_k(2_000), "2.0k");
+        assert_eq!(fmt_k(2_200), "2.2k");
+        assert_eq!(fmt_k(25_600), "25.6k");
+        assert_eq!(fmt_k(86_600), "86.6k");
+        assert_eq!(fmt_k(1_000_000), "1.0M");
+        assert_eq!(fmt_k(1_500_000), "1.5M");
+    }
+
+    #[test]
+    fn fmt_eta_tiers() {
+        assert_eq!(fmt_eta(-5), "now");
+        assert_eq!(fmt_eta(0), "now");
+        assert_eq!(fmt_eta(30), "0m"); // %dm with integer division, like bash
+        assert_eq!(fmt_eta(90), "1m");
+        assert_eq!(fmt_eta(3_600), "1h");
+        assert_eq!(fmt_eta(3_660), "1h1m");
+        assert_eq!(fmt_eta(86_400), "1d");
+        assert_eq!(fmt_eta(90_000), "1d1h");
+        assert_eq!(fmt_eta(273_600), "3d4h"); // 5h-window reset ETA in the golden
+    }
+}
diff --git a/rust/src/lib.rs b/rust/src/lib.rs
index 819b919..7d13ae2 100644
--- a/rust/src/lib.rs
+++ b/rust/src/lib.rs
@@ -2,3 +2,5 @@
 //!
 //! Pure domain (deterministic, golden-testable) and a thin stateful edge.
 //! Modules land bottom-up, one slice per PR (see inbrace-tech/tokenline#27).
+
+pub mod fmt;