diff --git a/library/compiler-builtins/libm/Cargo.toml b/library/compiler-builtins/libm/Cargo.toml
index fc881b77e548..820c013478f4 100644
--- a/library/compiler-builtins/libm/Cargo.toml
+++ b/library/compiler-builtins/libm/Cargo.toml
@@ -46,6 +46,7 @@ members = [
   "crates/libm-macros",
   "crates/libm-test",
   "crates/musl-math-sys",
+  "crates/util",
 ]
 default-members = [
   ".",
diff --git a/library/compiler-builtins/libm/crates/libm-test/src/mpfloat.rs b/library/compiler-builtins/libm/crates/libm-test/src/mpfloat.rs
index f71e72cd5712..092f5f1d24d7 100644
--- a/library/compiler-builtins/libm/crates/libm-test/src/mpfloat.rs
+++ b/library/compiler-builtins/libm/crates/libm-test/src/mpfloat.rs
@@ -471,6 +471,32 @@ impl MpOp for crate::op::lgammaf_r::Routine {
     }
 }
 
+/* stub implementations so we don't need to special case them */
+
+impl MpOp for crate::op::nextafter::Routine {
+    type MpTy = MpFloat;
+
+    fn new_mp() -> Self::MpTy {
+        unimplemented!("nextafter does not yet have a MPFR operation");
+    }
+
+    fn run(_this: &mut Self::MpTy, _input: Self::RustArgs) -> Self::RustRet {
+        unimplemented!("nextafter does not yet have a MPFR operation");
+    }
+}
+
+impl MpOp for crate::op::nextafterf::Routine {
+    type MpTy = MpFloat;
+
+    fn new_mp() -> Self::MpTy {
+        unimplemented!("nextafter does not yet have a MPFR operation");
+    }
+
+    fn run(_this: &mut Self::MpTy, _input: Self::RustArgs) -> Self::RustRet {
+        unimplemented!("nextafter does not yet have a MPFR operation");
+    }
+}
+
 /// `rug` does not provide `remquo` so this exposes `mpfr_remquo`. See rug#76.
 fn mpfr_remquo(r: &mut MpFloat, x: &MpFloat, y: &MpFloat, round: Round) -> (Ordering, c_long) {
     let r = r.as_raw_mut();
diff --git a/library/compiler-builtins/libm/crates/util/Cargo.toml b/library/compiler-builtins/libm/crates/util/Cargo.toml
new file mode 100644
index 000000000000..acf5db704b15
--- /dev/null
+++ b/library/compiler-builtins/libm/crates/util/Cargo.toml
@@ -0,0 +1,19 @@
+[package]
+name = "util"
+version = "0.1.0"
+edition = "2021"
+publish = false
+
+[features]
+default = ["build-musl", "build-mpfr", "unstable-float"]
+build-musl = ["libm-test/build-musl", "dep:musl-math-sys"]
+build-mpfr = ["libm-test/build-mpfr", "dep:az", "dep:rug"]
+unstable-float = ["libm/unstable-float", "libm-test/unstable-float", "rug?/nightly-float"]
+
+[dependencies]
+az = { version = "1.2.1", optional = true }
+libm = { path = "../..", default-features = false }
+libm-macros = { path = "../libm-macros" }
+libm-test = { path = "../libm-test", default-features = false }
+musl-math-sys = { path = "../musl-math-sys", optional = true }
+rug = { version = "1.26.1", optional = true, default-features = false, features = ["float", "std"] }
diff --git a/library/compiler-builtins/libm/crates/util/build.rs b/library/compiler-builtins/libm/crates/util/build.rs
new file mode 100644
index 000000000000..0745ef3dd6f3
--- /dev/null
+++ b/library/compiler-builtins/libm/crates/util/build.rs
@@ -0,0 +1,9 @@
+#![allow(unexpected_cfgs)]
+
+#[path = "../../configure.rs"]
+mod configure;
+
+fn main() {
+    let cfg = configure::Config::from_env();
+    configure::emit_libm_config(&cfg);
+}
diff --git a/library/compiler-builtins/libm/crates/util/src/main.rs b/library/compiler-builtins/libm/crates/util/src/main.rs
new file mode 100644
index 000000000000..f7bd31bb689c
--- /dev/null
+++ b/library/compiler-builtins/libm/crates/util/src/main.rs
@@ -0,0 +1,243 @@
+//! Helper CLI utility for common tasks.
+
+#![cfg_attr(f16_enabled, feature(f16))]
+#![cfg_attr(f128_enabled, feature(f128))]
+
+use std::any::type_name;
+use std::env;
+use std::str::FromStr;
+
+#[cfg(feature = "build-mpfr")]
+use az::Az;
+#[cfg(feature = "build-mpfr")]
+use libm_test::mpfloat::MpOp;
+use libm_test::{MathOp, TupleCall};
+
+const USAGE: &str = "\
+usage:
+
+cargo run -p util -- <SUBCOMMAND>
+
+SUBCOMMAND:
+    eval <BASIS> <OP> inputs...
+        Evaulate the expression with a given basis. This can be useful for
+        running routines with a debugger, or quickly checking input. Examples:
+        * eval musl sinf 1.234 # print the results of musl sinf(1.234f32)
+        * eval mpfr pow 1.234 2.432 # print the results of mpfr pow(1.234, 2.432)
+";
+
+fn main() {
+    let args = env::args().collect::<Vec<_>>();
+    let str_args = args.iter().map(|s| s.as_str()).collect::<Vec<_>>();
+
+    match &str_args.as_slice()[1..] {
+        ["eval", basis, op, inputs @ ..] => do_eval(basis, op, inputs),
+        _ => {
+            println!("{USAGE}\nunrecognized input `{str_args:?}`");
+            std::process::exit(1);
+        }
+    }
+}
+
+macro_rules! handle_call {
+    (
+        fn_name: $fn_name:ident,
+        CFn: $CFn:ty,
+        RustFn: $RustFn:ty,
+        RustArgs: $RustArgs:ty,
+        attrs: [$($attr:meta),*],
+        extra: ($basis:ident, $op:ident, $inputs:ident),
+        fn_extra: $musl_fn:expr,
+    ) => {
+        $(#[$attr])*
+        if $op == stringify!($fn_name) {
+            type Op = libm_test::op::$fn_name::Routine;
+
+            let input = <$RustArgs>::parse($inputs);
+            let libm_fn: <Op as MathOp>::RustFn = libm::$fn_name;
+
+            let output = match $basis {
+                "libm" => input.call(libm_fn),
+                #[cfg(feature = "build-musl")]
+                "musl" => {
+                    let musl_fn: <Op as MathOp>::CFn =
+                        $musl_fn.unwrap_or_else(|| panic!("no musl function for {}", $op));
+                    input.call(musl_fn)
+                }
+                #[cfg(feature = "build-mpfr")]
+                "mpfr" => {
+                    let mut mp = <Op as MpOp>::new_mp();
+                    Op::run(&mut mp, input)
+                }
+                _ => panic!("unrecognized or disabled basis '{}'", $basis),
+            };
+            println!("{output:?}");
+            return;
+        }
+    };
+}
+
+/// Evaluate the specified operation with a given basis.
+fn do_eval(basis: &str, op: &str, inputs: &[&str]) {
+    libm_macros::for_each_function! {
+        callback: handle_call,
+        emit_types: [CFn, RustFn, RustArgs],
+        extra: (basis, op, inputs),
+        fn_extra: match MACRO_FN_NAME {
+            copysignf16 | copysignf128 | fabsf16 | fabsf128 => None,
+            _ => Some(musl_math_sys::MACRO_FN_NAME)
+        }
+    }
+
+    panic!("no operation matching {op}");
+}
+
+/// Parse a tuple from a space-delimited string.
+trait ParseTuple {
+    fn parse(input: &[&str]) -> Self;
+}
+
+macro_rules! impl_parse_tuple {
+    ($ty:ty) => {
+        impl ParseTuple for ($ty,) {
+            fn parse(input: &[&str]) -> Self {
+                assert_eq!(input.len(), 1, "expected a single argument, got {input:?}");
+                (parse(input, 0),)
+            }
+        }
+
+        impl ParseTuple for ($ty, $ty) {
+            fn parse(input: &[&str]) -> Self {
+                assert_eq!(input.len(), 2, "expected two arguments, got {input:?}");
+                (parse(input, 0), parse(input, 1))
+            }
+        }
+
+        impl ParseTuple for ($ty, i32) {
+            fn parse(input: &[&str]) -> Self {
+                assert_eq!(input.len(), 2, "expected two arguments, got {input:?}");
+                (parse(input, 0), parse(input, 1))
+            }
+        }
+
+        impl ParseTuple for (i32, $ty) {
+            fn parse(input: &[&str]) -> Self {
+                assert_eq!(input.len(), 2, "expected two arguments, got {input:?}");
+                (parse(input, 0), parse(input, 1))
+            }
+        }
+
+        impl ParseTuple for ($ty, $ty, $ty) {
+            fn parse(input: &[&str]) -> Self {
+                assert_eq!(input.len(), 2, "expected three arguments, got {input:?}");
+                (parse(input, 0), parse(input, 1), parse(input, 3))
+            }
+        }
+    };
+}
+
+#[allow(unused_macros)]
+#[cfg(feature = "build-mpfr")]
+macro_rules! impl_parse_tuple_via_rug {
+    ($ty:ty) => {
+        impl ParseTuple for ($ty,) {
+            fn parse(input: &[&str]) -> Self {
+                assert_eq!(input.len(), 1, "expected a single argument, got {input:?}");
+                (parse_rug(input, 0),)
+            }
+        }
+
+        impl ParseTuple for ($ty, $ty) {
+            fn parse(input: &[&str]) -> Self {
+                assert_eq!(input.len(), 2, "expected two arguments, got {input:?}");
+                (parse_rug(input, 0), parse_rug(input, 1))
+            }
+        }
+
+        impl ParseTuple for ($ty, i32) {
+            fn parse(input: &[&str]) -> Self {
+                assert_eq!(input.len(), 2, "expected two arguments, got {input:?}");
+                (parse_rug(input, 0), parse(input, 1))
+            }
+        }
+
+        impl ParseTuple for (i32, $ty) {
+            fn parse(input: &[&str]) -> Self {
+                assert_eq!(input.len(), 2, "expected two arguments, got {input:?}");
+                (parse(input, 0), parse_rug(input, 1))
+            }
+        }
+
+        impl ParseTuple for ($ty, $ty, $ty) {
+            fn parse(input: &[&str]) -> Self {
+                assert_eq!(input.len(), 2, "expected three arguments, got {input:?}");
+                (parse_rug(input, 0), parse_rug(input, 1), parse_rug(input, 3))
+            }
+        }
+    };
+}
+
+// Fallback for when Rug is not built.
+#[allow(unused_macros)]
+#[cfg(not(feature = "build-mpfr"))]
+macro_rules! impl_parse_tuple_via_rug {
+    ($ty:ty) => {
+        impl ParseTuple for ($ty,) {
+            fn parse(_input: &[&str]) -> Self {
+                panic!("parsing this type requires the `build-mpfr` feature")
+            }
+        }
+
+        impl ParseTuple for ($ty, $ty) {
+            fn parse(_input: &[&str]) -> Self {
+                panic!("parsing this type requires the `build-mpfr` feature")
+            }
+        }
+
+        impl ParseTuple for ($ty, i32) {
+            fn parse(_input: &[&str]) -> Self {
+                panic!("parsing this type requires the `build-mpfr` feature")
+            }
+        }
+
+        impl ParseTuple for (i32, $ty) {
+            fn parse(_input: &[&str]) -> Self {
+                panic!("parsing this type requires the `build-mpfr` feature")
+            }
+        }
+
+        impl ParseTuple for ($ty, $ty, $ty) {
+            fn parse(_input: &[&str]) -> Self {
+                panic!("parsing this type requires the `build-mpfr` feature")
+            }
+        }
+    };
+}
+
+impl_parse_tuple!(f32);
+impl_parse_tuple!(f64);
+
+#[cfg(f16_enabled)]
+impl_parse_tuple_via_rug!(f16);
+#[cfg(f128_enabled)]
+impl_parse_tuple_via_rug!(f128);
+
+/// Try to parse the number, printing a nice message on failure.
+fn parse<F: FromStr>(input: &[&str], idx: usize) -> F {
+    let s = input[idx];
+    s.parse().unwrap_or_else(|_| panic!("invalid {} input '{s}'", type_name::<F>()))
+}
+
+/// Try to parse the float type going via `rug`, for `f16` and `f128` which don't yet implement
+/// `FromStr`.
+#[cfg(feature = "build-mpfr")]
+fn parse_rug<F: libm_test::Float>(input: &[&str], idx: usize) -> F
+where
+    rug::Float: az::Cast<F>,
+{
+    let s = input[idx];
+    let x =
+        rug::Float::parse(s).unwrap_or_else(|_| panic!("invalid {} input '{s}'", type_name::<F>()));
+    let x = rug::Float::with_val(F::BITS, x);
+    x.az()
+}