diff --git a/.cargo/config.toml b/.cargo/config.toml
index f9029a13..3bbcf928 100644
--- a/.cargo/config.toml
+++ b/.cargo/config.toml
@@ -19,6 +19,16 @@ rustflags = [
 # which wraps it in an ISO and boots it under QEMU.
 runner = "target/release/xtask test-runner"
 
+# Userspace target: vibix std programs cross-compiled with -Z build-std.
+# The target spec JSON lives at the workspace root; rustflags here apply
+# when --target=x86_64-unknown-vibix.json is passed explicitly by xtask.
+[target.x86_64-unknown-vibix]
+rustflags = [
+  "-C", "relocation-model=static",
+  "-C", "no-redzone=yes",
+  "-C", "force-frame-pointers=yes",
+]
+
 # `build-std` is intentionally NOT in [unstable] here — it would apply
 # to host `cargo test --lib` too and clash with the sysroot's std.
 # xtask passes `-Z build-std=...` explicitly whenever it invokes cargo
diff --git a/x86_64-unknown-vibix.json b/x86_64-unknown-vibix.json
new file mode 100644
index 00000000..c75e95bd
--- /dev/null
+++ b/x86_64-unknown-vibix.json
@@ -0,0 +1,27 @@
+{
+  "llvm-target": "x86_64-unknown-none-elf",
+  "data-layout": "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128",
+  "arch": "x86_64",
+  "target-endian": "little",
+  "target-pointer-width": "64",
+  "target-c-int-width": "32",
+  "os": "vibix",
+  "env": "",
+  "vendor": "unknown",
+  "linker-flavor": "gnu-lld",
+  "linker": "rust-lld",
+  "pre-link-args": {
+    "gnu-lld": ["-nostdlib", "-static"]
+  },
+  "panic-strategy": "abort",
+  "disable-redzone": true,
+  "features": "+sse,+sse2",
+  "has-thread-local": true,
+  "tls-model": "initial-exec",
+  "position-independent-executables": false,
+  "static-position-independent-executables": false,
+  "relocation-model": "static",
+  "executables": true,
+  "max-atomic-width": 64,
+  "crt-objects-fallback": "false"
+}
diff --git a/xtask/Cargo.toml b/xtask/Cargo.toml
index f742607c..32fb4524 100644
--- a/xtask/Cargo.toml
+++ b/xtask/Cargo.toml
@@ -11,3 +11,4 @@ path = "src/main.rs"
 object = { version = "0.36", default-features = false, features = ["read", "std"] }
 rustc-demangle = "0.1"
 gimli = { version = "0.31", default-features = false, features = ["read-all"] }
+serde_json = "1"
diff --git a/xtask/src/main.rs b/xtask/src/main.rs
index 43509b74..2052b64e 100644
--- a/xtask/src/main.rs
+++ b/xtask/src/main.rs
@@ -58,6 +58,10 @@ const KERNEL_BUILD_STD_ARGS: &[&str] = &[
     "build-std-features=compiler-builtins-mem",
 ];
 
+/// Custom target spec for vibix userspace (std programs cross-compiled
+/// with `-Z build-std`). The JSON file lives at the workspace root.
+const VIBIX_USERSPACE_TARGET: &str = "x86_64-unknown-vibix.json";
+
 // QEMU process exit codes produced by `isa-debug-exit` writing our
 // QemuExitCode values. See kernel/src/test_harness.rs.
 const QEMU_EXIT_SUCCESS: i32 = 65; // (0x20 << 1) | 1
@@ -393,6 +397,9 @@ fn main() -> R<()> {
             }
         }
         "clean" => clean()?,
+        "validate-target" => {
+            validate_vibix_target()?;
+        }
         "bench" => {
             // `xtask bench <target>`. Currently only `page-cache` is
             // wired (#743 — RFC 0007 host-side cold-mmap fault-latency
@@ -427,7 +434,7 @@ fn main() -> R<()> {
         other => {
             eprintln!("unknown subcommand: {other}");
             eprintln!(
-                "usage: cargo xtask [build|initrd|ext2-image|iso|run|test|test-unit|test-integration|smoke|pjdfstest|repro-fork|repro-fork-build|shell-pipeline|lint|isr-audit|nm-check|bench|fuzz|clean] [--release] [--fault-test] [--panic-test] [--bench] [--fork-trace] [--shard=I/N (test-integration only)]"
+                "usage: cargo xtask [build|initrd|ext2-image|iso|run|test|test-unit|test-integration|smoke|pjdfstest|repro-fork|repro-fork-build|shell-pipeline|lint|isr-audit|nm-check|validate-target|bench|fuzz|clean] [--release] [--fault-test] [--panic-test] [--bench] [--fork-trace] [--shard=I/N (test-integration only)]"
             );
             std::process::exit(2);
         }
@@ -3416,3 +3423,91 @@ repro: starting fork loop cycles=500 hb=50
         }
     }
 }
+
+// ─── validate-target ───────────────────────────────────────────────────────
+
+/// Validate that the `x86_64-unknown-vibix.json` target spec is well-formed
+/// and contains the required fields for vibix userspace cross-compilation.
+fn validate_vibix_target() -> R<()> {
+    let spec_path = workspace_root().join(VIBIX_USERSPACE_TARGET);
+    if !spec_path.exists() {
+        return Err(format!("target spec not found at {}", spec_path.display()).into());
+    }
+
+    let contents = fs::read_to_string(&spec_path)?;
+    let spec: serde_json::Value = serde_json::from_str(&contents)
+        .map_err(|e| format!("target spec {} is not valid JSON: {e}", spec_path.display()))?;
+
+    let obj = spec
+        .as_object()
+        .ok_or("target spec root is not a JSON object")?;
+
+    // Required fields and their expected values (where a specific value is
+    // mandated by the RFC). `None` means "must be present, any value ok".
+    let required: &[(&str, Option<&str>)] = &[
+        ("llvm-target", Some("x86_64-unknown-none-elf")),
+        ("arch", Some("x86_64")),
+        ("os", Some("vibix")),
+        ("linker-flavor", Some("gnu-lld")),
+        ("linker", Some("rust-lld")),
+        ("panic-strategy", Some("abort")),
+        ("relocation-model", Some("static")),
+        ("tls-model", Some("initial-exec")),
+        ("features", Some("+sse,+sse2")),
+        ("data-layout", None),
+        ("target-endian", Some("little")),
+        ("target-pointer-width", Some("64")),
+    ];
+
+    let mut errors = Vec::new();
+    for &(key, expected_val) in required {
+        match obj.get(key) {
+            None => errors.push(format!("missing required field: \"{key}\"")),
+            Some(val) => {
+                if let Some(expected) = expected_val {
+                    let actual = val.as_str().unwrap_or("");
+                    if actual != expected {
+                        errors.push(format!(
+                            "field \"{key}\": expected \"{expected}\", got \"{actual}\""
+                        ));
+                    }
+                }
+            }
+        }
+    }
+
+    // Boolean fields that must be true.
+    for key in ["has-thread-local", "disable-redzone"] {
+        match obj.get(key) {
+            None => errors.push(format!("missing required field: \"{key}\"")),
+            Some(val) => {
+                if val.as_bool() != Some(true) {
+                    errors.push(format!("field \"{key}\" must be true"));
+                }
+            }
+        }
+    }
+
+    // Boolean fields that must be false.
+    for key in ["position-independent-executables"] {
+        match obj.get(key) {
+            None => errors.push(format!("missing required field: \"{key}\"")),
+            Some(val) => {
+                if val.as_bool() != Some(false) {
+                    errors.push(format!("field \"{key}\" must be false"));
+                }
+            }
+        }
+    }
+
+    if errors.is_empty() {
+        println!("✓ target spec {} is well-formed", spec_path.display());
+        Ok(())
+    } else {
+        Err(format!(
+            "target spec validation failed:\n  • {}",
+            errors.join("\n  • ")
+        )
+        .into())
+    }
+}