diff --git a/node/src/commands/hook/posttool.ts b/node/src/commands/hook/posttool.ts
index 50965a7..5e483a5 100644
--- a/node/src/commands/hook/posttool.ts
+++ b/node/src/commands/hook/posttool.ts
@@ -23,6 +23,11 @@ interface PostToolOutput {
 export function createHookPosttoolCommand(): Command {
   return new Command("posttool")
     .description("PostToolUse hook handler (reads stdin, redacts secrets in output, writes JSON to stdout)")
+    // Tolerate extra flags/args the host harness appends to the hook command
+    // (e.g. Claude Code adds `--hook-json <data>`). Hook input comes from stdin,
+    // so anything else is unused — discard it instead of erroring out.
+    .allowUnknownOption()
+    .allowExcessArguments()
     .option("--format <format>", "Output format: claude (default, also Codex/Continue), cursor, gemini, windsurf", "claude")
     .action(async (opts) => {
       const format = (opts.format || "claude") as HookFormat;
diff --git a/node/src/commands/hook/pretool.ts b/node/src/commands/hook/pretool.ts
index 060354b..68024d8 100644
--- a/node/src/commands/hook/pretool.ts
+++ b/node/src/commands/hook/pretool.ts
@@ -95,6 +95,11 @@ function formatApprovalMessage(command: string, evaluation: CommandEvaluation):
 export function createHookPretoolCommand(): Command {
   return new Command("pretool")
     .description("PreToolUse hook handler (reads stdin, writes JSON decision to stdout)")
+    // Tolerate extra flags/args the host harness appends to the hook command
+    // (e.g. Claude Code adds `--hook-json <data>`). Hook input comes from stdin,
+    // so anything else is unused — discard it instead of erroring out.
+    .allowUnknownOption()
+    .allowExcessArguments()
     .option("--format <format>", "Output format: claude (default, also Codex/Continue), cursor, gemini, windsurf", "claude")
     .action(async (opts) => {
       const format = (opts.format || "claude") as HookFormat;
diff --git a/node/tests/hook-extra-args.test.ts b/node/tests/hook-extra-args.test.ts
new file mode 100644
index 0000000..60c1b31
--- /dev/null
+++ b/node/tests/hook-extra-args.test.ts
@@ -0,0 +1,50 @@
+import { describe, it, expect } from "vitest";
+import { spawnSync } from "child_process";
+import path from "path";
+
+// Regression: the host harness may append extra flags/args to the hook command.
+// Claude Code appends `--hook-json <data>`; hook input comes from stdin, so the
+// CLI must tolerate (discard) the extra flag instead of erroring (#180).
+
+const CLI_ENTRY = path.join(path.resolve(__dirname, ".."), "dist", "index.js");
+const PRETOOL_IN = JSON.stringify({ tool_name: "Bash", tool_input: { command: "ls" } });
+const POSTTOOL_IN = JSON.stringify({ tool_name: "Bash", tool_response: { output: "ok" } });
+
+function runHook(args: string): { code: number; out: any } {
+  const r = spawnSync(`node ${CLI_ENTRY} ${args}`, {
+    input: args.includes("posttool") ? POSTTOOL_IN : PRETOOL_IN,
+    encoding: "utf-8",
+    shell: true,
+    timeout: 30_000,
+  });
+  return { code: r.status ?? -1, out: JSON.parse(r.stdout || "{}") };
+}
+
+describe("hook commands tolerate harness-appended flags (#180)", () => {
+  it("pretool accepts --hook-json and still returns a decision", () => {
+    const { code, out } = runHook("hook pretool --hook-json '{}'");
+    expect(code).toBe(0);
+    expect(out.hookSpecificOutput?.permissionDecision).toBe("allow");
+  });
+
+  it("posttool accepts --hook-json", () => {
+    const { code, out } = runHook("hook posttool --hook-json '{\"x\":1}'");
+    expect(code).toBe(0);
+    expect(out.hookSpecificOutput?.hookEventName).toBe("PostToolUse");
+  });
+
+  it("a real option (--format) is still honored, not swallowed", () => {
+    // gemini "allow" emits an empty object, distinct from the claude shape.
+    const r = spawnSync(`node ${CLI_ENTRY} hook pretool --format gemini --hook-json '{}'`, {
+      input: PRETOOL_IN, encoding: "utf-8", shell: true, timeout: 30_000,
+    });
+    expect(r.status).toBe(0);
+    expect(r.stdout.trim()).toBe("{}");
+  });
+
+  it("still works with no extra flag (unchanged behavior)", () => {
+    const { code, out } = runHook("hook pretool");
+    expect(code).toBe(0);
+    expect(out.hookSpecificOutput?.permissionDecision).toBe("allow");
+  });
+});
diff --git a/python/rafter_cli/commands/hook.py b/python/rafter_cli/commands/hook.py
index 026f296..09c059f 100644
--- a/python/rafter_cli/commands/hook.py
+++ b/python/rafter_cli/commands/hook.py
@@ -13,7 +13,15 @@
 from ..core.command_interceptor import CommandInterceptor
 from ..scanners.regex_scanner import RegexScanner
 
-hook_app = typer.Typer(name="hook", help="Hook handlers for agent platform integration", no_args_is_help=True)
+# allow_extra_args / ignore_unknown_options: tolerate extra flags/args the host
+# harness appends to the hook command (e.g. Claude Code adds `--hook-json <data>`).
+# Hook input comes from stdin, so anything else is unused — discard, don't error.
+hook_app = typer.Typer(
+    name="hook",
+    help="Hook handlers for agent platform integration",
+    no_args_is_help=True,
+    context_settings={"allow_extra_args": True, "ignore_unknown_options": True},
+)
 
 _RISK_LABELS = {
     "critical": "CRITICAL", "high": "HIGH", "medium": "MEDIUM", "low": "LOW",
@@ -401,7 +409,10 @@ def _evaluate_write(tool_input: dict) -> dict:
     return {"decision": "deny", "reason": f"Secret detected in {file_path}: {', '.join(names)}"}
 
 
-@hook_app.command("pretool")
+@hook_app.command(
+    "pretool",
+    context_settings={"allow_extra_args": True, "ignore_unknown_options": True},
+)
 def pretool(
     format: str = typer.Option("claude", "--format", help="Output format: claude (default, also Codex/Continue), cursor, gemini, windsurf"),
 ):
@@ -449,7 +460,10 @@ def pretool(
         _write_pretool_decision({"decision": "allow"}, format)
 
 
-@hook_app.command("posttool")
+@hook_app.command(
+    "posttool",
+    context_settings={"allow_extra_args": True, "ignore_unknown_options": True},
+)
 def posttool(
     format: str = typer.Option("claude", "--format", help="Output format: claude (default, also Codex/Continue), cursor, gemini, windsurf"),
 ):
diff --git a/python/tests/test_hook_extra_args.py b/python/tests/test_hook_extra_args.py
new file mode 100644
index 0000000..038336b
--- /dev/null
+++ b/python/tests/test_hook_extra_args.py
@@ -0,0 +1,46 @@
+"""Regression: hook subcommands must tolerate harness-appended flags/args.
+
+Claude Code appends `--hook-json <data>` to the hook command; hook input comes
+from stdin, so the extra flag must be discarded, not rejected (#180). The
+context_settings must live on the SUBCOMMAND (pretool/posttool), not only the
+hook_app group — a group-level setting does not reach subcommand parsing.
+"""
+from __future__ import annotations
+
+import json
+
+from typer.testing import CliRunner
+
+from rafter_cli.commands.hook import hook_app
+
+runner = CliRunner()
+
+_PRETOOL_IN = '{"tool_name":"Bash","tool_input":{"command":"ls"}}'
+_POSTTOOL_IN = '{"tool_name":"Bash","tool_response":{"output":"ok"}}'
+
+
+def test_pretool_tolerates_hook_json():
+    r = runner.invoke(hook_app, ["pretool", "--hook-json", "{}"], input=_PRETOOL_IN)
+    assert r.exit_code == 0, r.output
+    assert json.loads(r.stdout)["hookSpecificOutput"]["permissionDecision"] == "allow"
+
+
+def test_posttool_tolerates_hook_json():
+    r = runner.invoke(hook_app, ["posttool", "--hook-json", '{"x":1}'], input=_POSTTOOL_IN)
+    assert r.exit_code == 0, r.output
+    assert json.loads(r.stdout)["hookSpecificOutput"]["hookEventName"] == "PostToolUse"
+
+
+def test_real_format_option_still_honored():
+    # gemini "allow" emits an empty object — proves --format wasn't swallowed.
+    r = runner.invoke(
+        hook_app, ["pretool", "--format", "gemini", "--hook-json", "{}"], input=_PRETOOL_IN
+    )
+    assert r.exit_code == 0, r.output
+    assert r.stdout.strip() == "{}"
+
+
+def test_no_extra_flag_unchanged():
+    r = runner.invoke(hook_app, ["pretool"], input=_PRETOOL_IN)
+    assert r.exit_code == 0, r.output
+    assert json.loads(r.stdout)["hookSpecificOutput"]["permissionDecision"] == "allow"
diff --git a/shared-docs/CLI_SPEC.md b/shared-docs/CLI_SPEC.md
index c2aaed1..0ee0ef1 100644
--- a/shared-docs/CLI_SPEC.md
+++ b/shared-docs/CLI_SPEC.md
@@ -945,6 +945,8 @@ On a `git commit` / `git push` (and on `Write`/`Edit`), the hook scans for secre
 
 **Bounded stdin read.** Both `hook pretool` and `hook posttool` bound their stdin read so a host that opens the hook's stdin but never writes/closes it (no EOF) cannot wedge the hook: after the bound elapses the hook reads whatever arrived (typically nothing), fails open (`allow` / no-op redaction), and the process **exits** — it does not merely emit a decision and keep running. The bound is **5000 ms** by default and is overridable via `RAFTER_HOOK_STDIN_TIMEOUT_MS` (positive integer milliseconds; non-positive or unparseable values fall back to the default). Both implementations honor the same env var identically.
 
+**Tolerates harness-appended flags.** Hook input arrives on **stdin**, so both subcommands ignore unknown options and extra positional args that an agent platform appends to the hook command — e.g. Claude Code adds `--hook-json <data>`. Such extras are discarded (the hook never errors on them); declared options like `--format` are still parsed normally.
+
 ### rafter hook posttool [OPTIONS]
 
 PostToolUse hook handler. Reads tool output from stdin, redacts any secrets found, and writes JSON to stdout.