diff --git a/src/reduce.zig b/src/reduce.zig
index f238125528..cd5d69b0c6 100644
--- a/src/reduce.zig
+++ b/src/reduce.zig
@@ -1,13 +1,34 @@
 const std = @import("std");
+const mem = std.mem;
 const Allocator = std.mem.Allocator;
 const assert = std.debug.assert;
+const fatal = @import("./main.zig").fatal;
 
 const usage =
-    \\zig reduce [source_file] [interestingness]
+    \\zig reduce [options] ./checker root_source_file.zig [-- [argv]]
+    \\
+    \\root_source_file.zig is relative to --main-mod-path.
+    \\
+    \\checker:
+    \\  An executable that communicates interestingness by returning these exit codes:
+    \\    exit(0):     interesting
+    \\    exit(1):     unknown (infinite loop or other mishap)
+    \\    exit(other): not interesting
+    \\
+    \\options:
+    \\  --mod [name]:[deps]:[src] Make a module available for dependency under the given name
+    \\      deps: [dep],[dep],...
+    \\      dep:  [[import=]name]
+    \\  --deps [dep],[dep],...    Set dependency names for the root package
+    \\      dep:  [[import=]name]
+    \\  --main-mod-path           Set the directory of the root module
+    \\
+    \\argv:
+    \\  Forwarded directly to the interestingness script.
     \\
 ;
 
-const Interestingness = enum { interesting, boring, unknown };
+const Interestingness = enum { interesting, unknown, boring };
 
 // Roadmap:
 // - add thread pool
@@ -22,13 +43,44 @@ const Interestingness = enum { interesting, boring, unknown };
 // - integrate the build system?
 
 pub fn main(gpa: Allocator, arena: Allocator, args: []const []const u8) !void {
-    const file_path = args[2];
-    const interestingness_argv_template = args[3..];
+    var opt_checker_path: ?[]const u8 = null;
+    var opt_root_source_file_path: ?[]const u8 = null;
+    var argv: []const []const u8 = &.{};
+
+    {
+        var i: usize = 2; // skip over "zig" and "reduce"
+        while (i < args.len) : (i += 1) {
+            const arg = args[i];
+            if (mem.startsWith(u8, arg, "-")) {
+                if (mem.eql(u8, arg, "-h") or mem.eql(u8, arg, "--help")) {
+                    const stdout = std.io.getStdOut().writer();
+                    try stdout.writeAll(usage);
+                    return std.process.cleanExit();
+                } else if (mem.eql(u8, arg, "--")) {
+                    argv = args[i + 1 ..];
+                    break;
+                } else {
+                    fatal("unrecognized parameter: '{s}'", .{arg});
+                }
+            } else if (opt_checker_path == null) {
+                opt_checker_path = arg;
+            } else if (opt_root_source_file_path == null) {
+                opt_root_source_file_path = arg;
+            } else {
+                fatal("unexpected extra parameter: '{s}'", .{arg});
+            }
+        }
+    }
+
+    const checker_path = opt_checker_path orelse
+        fatal("missing interestingness checker argument; see -h for usage", .{});
+    const root_source_file_path = opt_root_source_file_path orelse
+        fatal("missing root source file path argument; see -h for usage", .{});
 
     var interestingness_argv: std.ArrayListUnmanaged([]const u8) = .{};
-    try interestingness_argv.ensureUnusedCapacity(arena, interestingness_argv_template.len + 1);
-    interestingness_argv.appendSliceAssumeCapacity(interestingness_argv_template);
-    interestingness_argv.appendAssumeCapacity(file_path);
+    try interestingness_argv.ensureUnusedCapacity(arena, argv.len + 1);
+    interestingness_argv.appendAssumeCapacity(checker_path);
+    interestingness_argv.appendSliceAssumeCapacity(argv);
 
     var rendered = std.ArrayList(u8).init(gpa);
     defer rendered.deinit();
@@ -38,7 +90,7 @@ pub fn main(gpa: Allocator, arena: Allocator, args: []const []const u8) !void {
 
     const source_code = try std.fs.cwd().readFileAllocOptions(
         arena,
-        file_path,
+        root_source_file_path,
         std.math.maxInt(u32),
         null,
         1,
@@ -55,38 +107,34 @@ pub fn main(gpa: Allocator, arena: Allocator, args: []const []const u8) !void {
     var next_gut_fn_index: u32 = 0;
     var fixups: std.zig.Ast.Fixups = .{};
 
+    {
+        // smoke test the interestingness check
+        switch (try runCheck(arena, interestingness_argv.items)) {
+            .interesting => {},
+            .boring, .unknown => |t| {
+                fatal("interestingness check returned {s} for unmodified input\n", .{
+                    @tagName(t),
+                });
+            },
+        }
+    }
+
     while (true) {
         try fixups.gut_functions.put(arena, next_gut_fn_index, {});
 
         rendered.clearRetainingCapacity();
         try tree.renderToArrayList(&rendered, fixups);
 
-        if (std.mem.eql(u8, rendered.items, prev_rendered.items)) {
+        if (mem.eql(u8, rendered.items, prev_rendered.items)) {
             std.debug.print("no remaining transformations\n", .{});
             break;
         }
         prev_rendered.clearRetainingCapacity();
         try prev_rendered.appendSlice(rendered.items);
 
-        try std.fs.cwd().writeFile(file_path, rendered.items);
+        try std.fs.cwd().writeFile(root_source_file_path, rendered.items);
 
-        const result = try std.process.Child.run(.{
-            .allocator = arena,
-            .argv = interestingness_argv.items,
-        });
-        if (result.stderr.len != 0)
-            std.debug.print("{s}", .{result.stderr});
-        const interestingness: Interestingness = switch (result.term) {
-            .Exited => |code| switch (code) {
-                0 => .interesting,
-                1 => .unknown,
-                else => .boring,
-            },
-            else => b: {
-                std.debug.print("interestingness check aborted unexpectedly\n", .{});
-                break :b .boring;
-            },
-        };
+        const interestingness = try runCheck(arena, interestingness_argv.items);
         std.debug.print("{s}\n", .{@tagName(interestingness)});
         switch (interestingness) {
             .interesting => {
@@ -104,3 +152,27 @@ pub fn main(gpa: Allocator, arena: Allocator, args: []const []const u8) !void {
     }
     return std.process.cleanExit();
 }
+
+fn termToInteresting(term: std.process.Child.Term) Interestingness {
+    return switch (term) {
+        .Exited => |code| switch (code) {
+            0 => .interesting,
+            1 => .unknown,
+            else => .boring,
+        },
+        else => b: {
+            std.debug.print("interestingness check aborted unexpectedly\n", .{});
+            break :b .boring;
+        },
+    };
+}
+
+fn runCheck(arena: std.mem.Allocator, argv: []const []const u8) !Interestingness {
+    const result = try std.process.Child.run(.{
+        .allocator = arena,
+        .argv = argv,
+    });
+    if (result.stderr.len != 0)
+        std.debug.print("{s}", .{result.stderr});
+    return termToInteresting(result.term);
+}