diff --git a/web/components/workflows/StepPickerModal.tsx b/web/components/workflows/StepPickerModal.tsx
new file mode 100644
index 0000000..17a4967
--- /dev/null
+++ b/web/components/workflows/StepPickerModal.tsx
@@ -0,0 +1,191 @@
+"use client";
+
+import { useMemo, useRef, useState } from "react";
+import { useQuery } from "@tanstack/react-query";
+import { api, WorkflowStep } from "@/lib/api";
+import { Modal } from "@/components/ui";
+
+type Tab = "all" | "bash" | "powershell" | "adhoc";
+
+function ShellBadge({ interpreter }: { interpreter: "bash" | "powershell" }) {
+  const isBash = interpreter === "bash";
+  return (
+    <span
+      className={`rounded px-1.5 py-0.5 font-mono text-[10px] uppercase ${
+        isBash ? "bg-bash/15 text-bash" : "bg-pwsh/15 text-pwsh"
+      }`}
+    >
+      {isBash ? "bash" : "pwsh"}
+    </span>
+  );
+}
+
+function DefaultBadge() {
+  return (
+    <span className="rounded bg-surface-2 px-1.5 py-0.5 font-mono text-[10px] uppercase text-text-secondary">
+      default
+    </span>
+  );
+}
+
+function StepCard({ step, onAdd }: { step: WorkflowStep; onAdd: () => void }) {
+  return (
+    <button
+      onClick={onAdd}
+      className="group relative rounded-[10px] border border-border bg-surface-2 p-3 text-left transition-colors hover:border-signal/55"
+    >
+      <span className="absolute right-3 top-3 text-xs font-semibold text-signal opacity-0 group-hover:opacity-100">
+        + Add
+      </span>
+      <div className="mb-1.5 flex items-center gap-2">
+        <ShellBadge interpreter={step.interpreter} />
+        {step.source === "default" && <DefaultBadge />}
+        <span className="text-sm font-medium text-text-primary">{step.name}</span>
+      </div>
+      {step.description && <p className="text-xs text-text-secondary">{step.description}</p>}
+      <div className="mt-2 flex flex-wrap gap-1.5">
+        {(step.declared_inputs ?? []).map((p) => (
+          <span key={p.name} className="rounded border border-border bg-background px-1.5 py-0.5 font-mono text-[10px] text-text-secondary">
+            in {p.name}
+          </span>
+        ))}
+        {(step.declared_outputs ?? []).map((o) => (
+          <span key={o} className="rounded border border-signal/35 bg-background px-1.5 py-0.5 font-mono text-[10px] text-signal">
+            out {o}
+          </span>
+        ))}
+      </div>
+    </button>
+  );
+}
+
+export function StepPickerModal({
+  open,
+  onClose,
+  onSelect,
+  onAddAdhoc,
+  onImportAdhoc,
+}: {
+  open: boolean;
+  onClose: () => void;
+  onSelect: (stepId: string) => void;
+  onAddAdhoc: () => void;
+  onImportAdhoc: (file: File) => void;
+}) {
+  const { data: library } = useQuery({ queryKey: ["steps"], queryFn: api.listSteps });
+  const [search, setSearch] = useState("");
+  const [tab, setTab] = useState<Tab>("all");
+  const fileRef = useRef<HTMLInputElement>(null);
+
+  const filtered = useMemo(() => {
+    const q = search.toLowerCase();
+    return (library ?? []).filter(
+      (s) =>
+        (s.name.toLowerCase().includes(q) || (s.description ?? "").toLowerCase().includes(q)) &&
+        (tab === "all" || tab === "adhoc" ? true : s.interpreter === tab),
+    );
+  }, [library, search, tab]);
+
+  const group = (source: "default" | "shared", interp: "bash" | "powershell") =>
+    filtered.filter(
+      (s) => s.interpreter === interp && (source === "default" ? s.source === "default" : s.source !== "default"),
+    );
+
+  const groups: { label: string; steps: WorkflowStep[] }[] = [
+    { label: "Default · Bash", steps: group("default", "bash") },
+    { label: "Default · PowerShell", steps: group("default", "powershell") },
+    { label: "Shared · Bash", steps: group("shared", "bash") },
+    { label: "Shared · PowerShell", steps: group("shared", "powershell") },
+  ];
+
+  const showLibrary = tab !== "adhoc";
+  const showAdhocCards = tab === "all" || tab === "adhoc";
+
+  return (
+    <Modal open={open} onClose={onClose} title="Add a step" wide>
+      <div className="space-y-4">
+        <input
+          autoFocus
+          className="w-full rounded-lg border border-border bg-surface-2 px-3 py-2 text-sm text-text-primary placeholder-text-secondary/50 focus:border-signal focus:outline-none focus:ring-1 focus:ring-signal"
+          placeholder="Search steps by name or description…"
+          value={search}
+          onChange={(e) => setSearch(e.target.value)}
+        />
+
+        <div className="flex gap-1.5">
+          {(["all", "bash", "powershell", "adhoc"] as Tab[]).map((t) => (
+            <button
+              key={t}
+              onClick={() => setTab(t)}
+              className={`rounded-full border px-3 py-1 text-xs capitalize ${
+                tab === t
+                  ? "border-signal/50 bg-signal/15 text-signal"
+                  : "border-border bg-surface-2 text-text-secondary hover:text-text-primary"
+              }`}
+            >
+              {t === "all" ? "All" : t === "powershell" ? "PowerShell" : t === "adhoc" ? "Ad-hoc" : "Bash"}
+            </button>
+          ))}
+        </div>
+
+        {showAdhocCards && (
+          <div className="grid grid-cols-2 gap-2.5">
+            <button
+              onClick={onAddAdhoc}
+              className="flex min-h-[74px] items-center justify-center gap-2 rounded-[10px] border border-dashed border-border text-sm text-text-secondary hover:border-signal/55 hover:text-signal"
+            >
+              + New ad-hoc step
+            </button>
+            <button
+              onClick={() => fileRef.current?.click()}
+              className="flex min-h-[74px] items-center justify-center gap-2 rounded-[10px] border border-dashed border-border text-sm text-text-secondary hover:border-signal/55 hover:text-signal"
+            >
+              ⬆ Import ad-hoc from file
+            </button>
+            <input
+              ref={fileRef}
+              type="file"
+              accept="application/json"
+              className="hidden"
+              onChange={(e) => {
+                const f = e.target.files?.[0];
+                if (f) onImportAdhoc(f);
+                e.target.value = "";
+              }}
+            />
+          </div>
+        )}
+
+        {showLibrary &&
+          groups.map(
+            (g) =>
+              g.steps.length > 0 && (
+                <div key={g.label}>
+                  <div className="mb-2.5 flex items-center gap-2 text-[11px] font-bold uppercase tracking-wide text-text-secondary">
+                    {g.label}
+                    <span className="h-px flex-1 bg-border" />
+                  </div>
+                  <div className="grid grid-cols-2 gap-2.5">
+                    {g.steps.map((s) => (
+                      <StepCard key={s.step_id} step={s} onAdd={() => onSelect(s.step_id)} />
+                    ))}
+                  </div>
+                </div>
+              ),
+          )}
+
+        {showLibrary && filtered.length === 0 && (
+          <p className="text-sm text-text-secondary">No steps match your search.</p>
+        )}
+
+        <p className="text-xs text-text-secondary">
+          Click a card to append it to the workflow · manage the library on the{" "}
+          <a href="/steps" className="text-signal hover:underline">
+            Steps
+          </a>{" "}
+          page.
+        </p>
+      </div>
+    </Modal>
+  );
+}