diff --git a/rust/.gitignore b/rust/.gitignore
new file mode 100644
index 0000000..ea8c4bf
--- /dev/null
+++ b/rust/.gitignore
@@ -0,0 +1 @@
+/target
diff --git a/rust/Cargo.lock b/rust/Cargo.lock
new file mode 100644
index 0000000..a3dfa35
--- /dev/null
+++ b/rust/Cargo.lock
@@ -0,0 +1,234 @@
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+# It is not intended for manual editing.
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+
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+ "unicode-ident",
+]
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+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "tokenline"
+version = "0.1.0"
+dependencies = [
+ "jiff",
+ "serde",
+ "serde_json",
+]
+
+[[package]]
+name = "unicode-ident"
+version = "1.0.24"
+source = "registry+https://github.com/rust-lang/crates.io-index"
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+
+[[package]]
+name = "windows-link"
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+source = "registry+https://github.com/rust-lang/crates.io-index"
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+
+[[package]]
+name = "zmij"
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+source = "registry+https://github.com/rust-lang/crates.io-index"
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diff --git a/rust/Cargo.toml b/rust/Cargo.toml
new file mode 100644
index 0000000..08945d4
--- /dev/null
+++ b/rust/Cargo.toml
@@ -0,0 +1,27 @@
+[package]
+name = "tokenline"
+version = "0.1.0"
+edition = "2024"
+rust-version = "1.85"
+description = "A cache-aware statusline for AI coding CLIs"
+license = "MIT"
+repository = "https://github.com/inbrace-tech/tokenline"
+
+[[bin]]
+name = "tokenline"
+path = "src/main.rs"
+
+[lib]
+name = "tokenline"
+path = "src/lib.rs"
+
+[dependencies]
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"
+jiff = "0.2"
+
+[profile.release]
+opt-level = "z"
+lto = true
+strip = true
+panic = "unwind" # catch_unwind MUST work; abort would be a non-zero exit
diff --git a/rust/src/fmt.rs b/rust/src/fmt.rs
new file mode 100644
index 0000000..16814c1
--- /dev/null
+++ b/rust/src/fmt.rs
@@ -0,0 +1,144 @@
+//! Formatting helpers, byte-for-byte parity with `tokenline.sh`.
+//!
+//! Carries `fmt_k` / `fmt_eta`, the 256-color palette, and the ISO-8601 → epoch
+//! parser.
+
+use jiff::Timestamp;
+
+/// Parse an RFC 3339 / ISO-8601 UTC timestamp to epoch seconds, or `None` on a
+/// malformed value. Replaces the bash `epoch_from_iso` (`date -d`): transcripts
+/// and rate-limit resets are fixed-format UTC, so `jiff::Timestamp` covers them
+/// without pulling a timezone database.
+pub fn iso8601_to_epoch(iso: &str) -> Option<i64> {
+    iso.parse::<Timestamp>().ok().map(|t| t.as_second())
+}
+
+/// 256-color SGR sequences, byte-identical to `tokenline.sh`'s `COLOR_*` /
+/// `STYLE_*` constants (`tokenline.sh:21-30`). Byte parity matters: the golden
+/// oracle diffs the raw escape sequences, so `RESET` is `[00m` (two digits),
+/// not `[0m`, exactly as the bash emits.
+pub mod color {
+    pub const GRAY: &str = "\x1b[38;5;244m";
+    pub const DARK_GRAY: &str = "\x1b[38;5;240m";
+    pub const CYAN: &str = "\x1b[38;5;51m";
+    pub const YELLOW: &str = "\x1b[38;5;226m";
+    pub const MAGENTA: &str = "\x1b[38;5;201m";
+    pub const ORANGE: &str = "\x1b[38;5;208m";
+    pub const RED: &str = "\x1b[38;5;196m";
+    pub const GREEN: &str = "\x1b[38;5;46m";
+    pub const RESET: &str = "\x1b[00m";
+    pub const BLINK: &str = "\x1b[1;5m";
+}
+
+/// 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 iso8601_to_epoch_parses_utc() {
+        // Exact epochs (verified independently). now in the golden = 1_783_000_000.
+        assert_eq!(
+            iso8601_to_epoch("2026-07-05T18:00:00Z"),
+            Some(1_783_274_400)
+        );
+        assert_eq!(
+            iso8601_to_epoch("2026-07-06T12:00:00Z"),
+            Some(1_783_339_200)
+        );
+        assert_eq!(
+            iso8601_to_epoch("2026-07-05T00:00:00Z"),
+            Some(1_783_209_600)
+        );
+    }
+
+    #[test]
+    fn iso8601_to_epoch_fractional_and_invalid() {
+        // Sub-second precision truncates to the whole second.
+        assert_eq!(
+            iso8601_to_epoch("2026-07-05T18:00:00.500Z"),
+            Some(1_783_274_400)
+        );
+        assert_eq!(iso8601_to_epoch("not a timestamp"), None);
+        assert_eq!(iso8601_to_epoch(""), None);
+    }
+
+    #[test]
+    fn palette_matches_bash_bytes() {
+        // Exact bytes captured from `tokenline.sh` output (cat -v): ESC[38;5;Nm.
+        assert_eq!(color::GRAY, "\x1b[38;5;244m");
+        assert_eq!(color::CYAN, "\x1b[38;5;51m");
+        assert_eq!(color::YELLOW, "\x1b[38;5;226m");
+        assert_eq!(color::MAGENTA, "\x1b[38;5;201m");
+        assert_eq!(color::ORANGE, "\x1b[38;5;208m");
+        assert_eq!(color::GREEN, "\x1b[38;5;46m");
+        assert_eq!(color::RED, "\x1b[38;5;196m");
+        assert_eq!(color::DARK_GRAY, "\x1b[38;5;240m");
+        // bash COLOR_RESET is [00m (two digits), STYLE_BLINK is [1;5m.
+        assert_eq!(color::RESET, "\x1b[00m");
+        assert_eq!(color::BLINK, "\x1b[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/input.rs b/rust/src/input.rs
new file mode 100644
index 0000000..1eee0e1
--- /dev/null
+++ b/rust/src/input.rs
@@ -0,0 +1,201 @@
+use serde::Deserialize;
+
+#[derive(Deserialize, Default)]
+pub struct RawInput {
+    #[serde(default)]
+    pub model: Model,
+    #[serde(default)]
+    pub context_window: ContextWindow,
+    #[serde(default)]
+    pub transcript_path: String,
+    #[serde(default)]
+    pub session_id: String,
+    #[serde(default)]
+    pub rate_limits: RateLimits,
+}
+
+#[derive(Deserialize, Default)]
+pub struct Model {
+    #[serde(default)]
+    pub display_name: String,
+}
+
+#[derive(Deserialize, Default)]
+pub struct ContextWindow {
+    #[serde(default)]
+    pub used_percentage: Option<f64>,
+    #[serde(default)]
+    pub context_window_size: Option<u64>,
+    #[serde(default)]
+    pub current_usage: Usage,
+}
+
+#[derive(Deserialize, Default)]
+pub struct Usage {
+    #[serde(default)]
+    pub input_tokens: u64,
+    #[serde(default)]
+    pub output_tokens: u64,
+    #[serde(default)]
+    pub cache_creation_input_tokens: u64,
+    #[serde(default)]
+    pub cache_read_input_tokens: u64,
+}
+
+#[derive(Deserialize, Default)]
+pub struct RateLimits {
+    #[serde(default)]
+    pub five_hour: Option<RlRaw>,
+    #[serde(default)]
+    pub seven_day: Option<RlRaw>,
+}
+
+#[derive(Deserialize, Default, Clone)]
+pub struct RlRaw {
+    #[serde(default)]
+    pub used_percentage: Option<f64>,
+    #[serde(default)]
+    pub resets_at: Option<String>,
+}
+
+#[derive(PartialEq, Debug)]
+pub enum Client {
+    ClaudeCode,
+    Antigravity,
+}
+
+pub struct Session {
+    pub model: String,
+    pub used_pct: Option<f64>,
+    pub tokens_limit: Option<u64>,
+    pub transcript_path: String,
+    pub session_id: String,
+    pub rl_5h: Option<RlRaw>,
+    pub rl_7d: Option<RlRaw>,
+    pub cur_input: u64,
+    pub cur_output: u64,
+    pub cur_cwrite: u64,
+    pub cur_cread: u64,
+    pub tokens_used: u64,
+    pub cli_client: Client,
+    pub is_gemini: bool,
+}
+
+impl Session {
+    pub fn from_raw(r: RawInput) -> Session {
+        let u = r.context_window.current_usage;
+        let tokens_used =
+            u.input_tokens + u.cache_creation_input_tokens + u.cache_read_input_tokens;
+
+        // Subagent transcript -> parent session (tokenline.sh:123-125)
+        // Normalize Windows backslashes once, up front, so all contains()/replace()
+        // logic below (written for forward slashes) works on both platforms.
+        let mut transcript_path = r.transcript_path.replace('\\', "/");
+        if transcript_path.contains("/subagents/") {
+            if let Some(parent) = std::path::Path::new(&transcript_path)
+                .parent()
+                .and_then(|p| p.parent())
+            {
+                transcript_path = format!("{}.jsonl", parent.display());
+            }
+        }
+
+        // Client + antigravity path correction (tokenline.sh:127-136)
+        let cli_client = if transcript_path.contains("/antigravity") {
+            Client::Antigravity
+        } else {
+            Client::ClaudeCode
+        };
+        if cli_client == Client::Antigravity && transcript_path.contains("/antigravity/") {
+            transcript_path = transcript_path.replace("/antigravity/", "/antigravity-cli/");
+        }
+
+        let is_gemini = r.model.display_name.to_lowercase().contains("gemini");
+
+        Session {
+            model: r.model.display_name,
+            used_pct: r.context_window.used_percentage,
+            tokens_limit: r.context_window.context_window_size,
+            transcript_path,
+            session_id: r.session_id,
+            rl_5h: r.rate_limits.five_hour,
+            rl_7d: r.rate_limits.seven_day,
+            cur_input: u.input_tokens,
+            cur_output: u.output_tokens,
+            cur_cwrite: u.cache_creation_input_tokens,
+            cur_cread: u.cache_read_input_tokens,
+            tokens_used,
+            cli_client,
+            is_gemini,
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const SAMPLE: &str = r#"{
+      "model": {"display_name": "Opus 4.8"},
+      "context_window": {
+        "used_percentage": 9.0, "context_window_size": 1000000,
+        "current_usage": {"input_tokens": 2, "output_tokens": 2000,
+          "cache_creation_input_tokens": 2200, "cache_read_input_tokens": 86600}
+      },
+      "transcript_path": "/home/u/.claude/projects/p/abc.jsonl",
+      "session_id": "abc",
+      "rate_limits": {
+        "five_hour": {"used_percentage": 12.0, "resets_at": "2026-07-05T18:00:00Z"},
+        "seven_day": {"used_percentage": 64.0, "resets_at": "2026-07-06T12:00:00Z"}
+      }
+    }"#;
+
+    #[test]
+    fn parses_and_derives() {
+        let raw: RawInput = serde_json::from_str(SAMPLE).unwrap();
+        let s = Session::from_raw(raw);
+        assert_eq!(s.model, "Opus 4.8");
+        assert_eq!(s.tokens_limit, Some(1_000_000));
+        assert_eq!(s.cur_cread, 86_600);
+        assert_eq!(s.tokens_used, 2 + 2200 + 86600); // input + cwrite + cread
+        assert_eq!(s.session_id, "abc");
+        assert!(!s.is_gemini);
+        assert_eq!(s.cli_client, Client::ClaudeCode);
+    }
+
+    #[test]
+    fn missing_fields_default_gracefully() {
+        let raw: RawInput = serde_json::from_str("{}").unwrap();
+        let s = Session::from_raw(raw);
+        assert_eq!(s.model, "");
+        assert_eq!(s.tokens_limit, None);
+        assert_eq!(s.tokens_used, 0);
+    }
+
+    #[test]
+    fn detects_gemini_and_antigravity() {
+        let raw: RawInput = serde_json::from_str(
+            r#"{"model":{"display_name":"Gemini 2.5 Pro"},
+                "transcript_path":"/x/antigravity/y/z.jsonl"}"#,
+        )
+        .unwrap();
+        let s = Session::from_raw(raw);
+        assert!(s.is_gemini);
+        assert_eq!(s.cli_client, Client::Antigravity);
+        assert!(s.transcript_path.contains("/antigravity-cli/"));
+    }
+
+    #[test]
+    fn normalizes_windows_backslash_paths() {
+        // Backslash subagent path resolves to the parent .jsonl, same as the unix case.
+        let raw: RawInput = serde_json::from_str(
+            r#"{"transcript_path":"C:\\Users\\x\\antigravity\\p\\subagents\\s\\t.jsonl"}"#,
+        )
+        .unwrap();
+        let s = Session::from_raw(raw);
+        assert_eq!(s.cli_client, Client::Antigravity);
+        assert!(s.transcript_path.contains("/antigravity-cli/"));
+        assert!(s.transcript_path.ends_with(".jsonl"));
+        assert!(!s.transcript_path.contains("/subagents/"));
+    }
+}
diff --git a/rust/src/lib.rs b/rust/src/lib.rs
new file mode 100644
index 0000000..4333d29
--- /dev/null
+++ b/rust/src/lib.rs
@@ -0,0 +1,8 @@
+//! tokenline — a cache-aware statusline for AI coding CLIs.
+//!
+//! 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;
+
+pub mod input;
diff --git a/rust/src/main.rs b/rust/src/main.rs
new file mode 100644
index 0000000..19193fd
--- /dev/null
+++ b/rust/src/main.rs
@@ -0,0 +1,6 @@
+// tokenline — a cache-aware statusline for AI coding CLIs.
+//
+// Slice 0: scaffold only. The real edge (stdin → now → cache_dir → render →
+// print → exit(0), with catch_unwind so a panic never crashes the host) lands
+// in the final slice; the pure domain modules land bottom-up before it.
+fn main() {}