diff --git a/packages/server/registry.js b/packages/server/registry.js
index 65c13ab..8f9cc5b 100644
--- a/packages/server/registry.js
+++ b/packages/server/registry.js
@@ -7,7 +7,10 @@ import { log } from "./logger.js";
 import * as store from "./store.js";
 import { clearScriptCache, runScript } from "./script-sandbox.js";
 import {
+  SET_STEP_SCRIPT,
   compileWorkflowScripts,
+  evaluateJsonata,
+  isJsonataTruthy,
   mergeStepData,
   namespacedPath,
   parseScriptStep,
@@ -209,7 +212,7 @@ export function createRegistry(server) {
     let next = ctx;
     for (const index of compiled.order) {
       const parsed = compiled.steps[index];
-      next = await executeStep(parsed, next, index, runId, runLog, key);
+      next = await runCompiledStep(parsed, next, index, runId, runLog, key);
     }
     return next;
   }
@@ -230,7 +233,7 @@ export function createRegistry(server) {
     for (const [orderIndex, stepIndex] of compiled.order.entries()) {
       const parsed = compiled.steps[stepIndex];
       const data = mergeStepData(parsed, outputsById, triggerData);
-      last = await executeStep(
+      last = await runCompiledStep(
         parsed,
         { ...ctx, data },
         orderIndex,
@@ -253,8 +256,9 @@ export function createRegistry(server) {
    * @param {import("pino").Logger} runLog
    * @param {string} key
    */
-  async function executeStep(parsed, ctx, index, runId, runLog, key) {
-    const { script, config } = parsed;
+  async function runCompiledStep(parsed, ctx, index, runId, runLog, key) {
+    const script = parsed.kind === "set" ? SET_STEP_SCRIPT : parsed.script;
+    const config = parsed.config;
     const step = await store.startStep({
       runId,
       index,
@@ -263,6 +267,23 @@ export function createRegistry(server) {
     });
     const stepLog = runLog.child({ stepId: step.id, script });
     try {
+      if (parsed.when) {
+        const whenResult = await evaluateJsonata(parsed.when, ctx);
+        if (!isJsonataTruthy(whenResult)) {
+          stepLog.debug({ when: parsed.when }, "step skipped");
+          await store.finishStep(step.id, "skipped", ctx);
+          return ctx;
+        }
+      }
+      if (parsed.kind === "set") {
+        if (ctx == null || typeof ctx !== "object" || Array.isArray(ctx)) {
+          throw new Error("set requires an object context");
+        }
+        const value = await evaluateJsonata(parsed.expression, ctx);
+        const result = { ...ctx, [parsed.as]: value };
+        await store.finishStep(step.id, "success", result);
+        return result;
+      }
       const result = await runScript(script, { ...ctx, config }, {
         log: stepLog,
         workflowName: key,
@@ -334,7 +355,8 @@ export function createRegistry(server) {
     for (const { workflow } of workflows.values()) {
       for (const raw of workflow.scripts ?? []) {
         try {
-          refs.add(parseScriptStep(raw).script);
+          const parsed = parseScriptStep(raw);
+          if (parsed.kind === "script") refs.add(parsed.script);
         } catch {
           // skip invalid steps
         }
diff --git a/packages/server/src/api/workflows.js b/packages/server/src/api/workflows.js
index 923140f..276e0d3 100644
--- a/packages/server/src/api/workflows.js
+++ b/packages/server/src/api/workflows.js
@@ -26,7 +26,8 @@ function scriptNames(workflow) {
   const names = [];
   for (const raw of workflow.scripts ?? []) {
     try {
-      names.push(parseScriptStep(raw).script);
+      const parsed = parseScriptStep(raw);
+      names.push(parsed.kind === "set" ? `set:${parsed.as}` : parsed.script);
     } catch {
       names.push(null);
     }
diff --git a/packages/server/store.js b/packages/server/store.js
index 6c76017..c50c584 100644
--- a/packages/server/store.js
+++ b/packages/server/store.js
@@ -126,7 +126,7 @@ export async function startStep({ runId, index, script, config = null }) {
 
 /**
  * @param {string} id
- * @param {"success" | "failed"} status
+ * @param {"success" | "failed" | "skipped"} status
  * @param {unknown} [output]
  * @param {Error | unknown} [err]
  */
diff --git a/packages/server/workflow-parse.js b/packages/server/workflow-parse.js
index 2c9e6d5..0aa9d5b 100644
--- a/packages/server/workflow-parse.js
+++ b/packages/server/workflow-parse.js
@@ -1,12 +1,35 @@
+import jsonata from "jsonata";
+
+const AS_IDENT = /^[A-Za-z_][A-Za-z0-9_]*$/;
+const RESERVED_AS = new Set(["data", "config"]);
+
+export const SET_STEP_SCRIPT = "set";
+
 /**
  * @typedef {{ alias: string, from: string }} NeedEdge
  * @typedef {{
+ *   kind: "script",
  *   script: string,
  *   config: unknown | null,
+ *   expression?: undefined,
+ *   as?: undefined,
  *   id: string | null,
  *   needsKind: "none" | "list" | "map",
  *   needs: NeedEdge[],
- * }} ParsedStep
+ *   when: string | null,
+ * }} ParsedScriptStep
+ * @typedef {{
+ *   kind: "set",
+ *   script: typeof SET_STEP_SCRIPT,
+ *   config: { expression: string, as: string },
+ *   expression: string,
+ *   as: string,
+ *   id: string | null,
+ *   needsKind: "none",
+ *   needs: NeedEdge[],
+ *   when: string | null,
+ * }} ParsedSetStep
+ * @typedef {ParsedScriptStep | ParsedSetStep} ParsedStep
  * @typedef {ParsedStep & { index: number }} CompiledStep
  * @typedef {{
  *   dagMode: boolean,
@@ -16,30 +39,36 @@
  */
 
 /**
- * @param {unknown} step
- * @returns {ParsedStep}
+ * Compile a JSONata source so save/load fails on syntax errors.
+ * @param {string} source
+ * @param {string} label
  */
-export function parseScriptStep(step) {
-  if (typeof step === "string") {
-    return {
-      script: step,
-      config: null,
-      id: null,
-      needsKind: "none",
-      needs: [],
-    };
+export function compileJsonata(source, label) {
+  try {
+    return jsonata(source);
+  } catch (err) {
+    const msg = err instanceof Error ? err.message : String(err);
+    throw new Error(`Invalid ${label}: ${msg}`);
   }
-  if (step?.script) {
-    const { needsKind, needs } = parseNeeds(step.needs);
-    return {
-      script: step.script,
-      config: step.config ?? null,
-      id: parseOptionalId(step.id),
-      needsKind,
-      needs,
-    };
-  }
-  throw new Error(`Invalid script step: ${JSON.stringify(step)}`);
+}
+
+/**
+ * @param {unknown} value
+ */
+export function isJsonataTruthy(value) {
+  if (value == null || value === false) return false;
+  if (Array.isArray(value) && value.length === 0) return false;
+  return true;
+}
+
+/**
+ * Evaluate JSONata against the full ctx (jsonata 2 may return a Promise).
+ * @param {string} source
+ * @param {unknown} ctx
+ */
+export async function evaluateJsonata(source, ctx) {
+  const result = compileJsonata(source, "expression").evaluate(ctx);
+  return await result;
 }
 
 /**
@@ -52,6 +81,56 @@ export function namespacedPath(owner, triggerPath) {
   return `/u/${owner}/${cleaned}`;
 }
 
+/**
+ * @param {unknown} step
+ * @returns {ParsedStep}
+ */
+export function parseScriptStep(step) {
+  if (typeof step === "string") {
+    return {
+      kind: "script",
+      script: step,
+      config: null,
+      id: null,
+      needsKind: "none",
+      needs: [],
+      when: null,
+    };
+  }
+  if (step == null || typeof step !== "object" || Array.isArray(step)) {
+    throw new Error(`Invalid script step: ${JSON.stringify(step)}`);
+  }
+
+  const hasScript = step.script != null && step.script !== "";
+  const hasSet = step.set != null;
+
+  if (hasScript && hasSet) {
+    throw new Error("Step cannot have both script and set");
+  }
+
+  if (hasSet) {
+    return parseSetStep(step);
+  }
+
+  if (hasScript) {
+    if (typeof step.script !== "string") {
+      throw new Error(`Invalid script step: ${JSON.stringify(step)}`);
+    }
+    const { needsKind, needs } = parseNeeds(step.needs);
+    return {
+      kind: "script",
+      script: step.script,
+      config: step.config ?? null,
+      id: parseOptionalId(step.id),
+      needsKind,
+      needs,
+      when: parseWhen(step.when),
+    };
+  }
+
+  throw new Error(`Invalid script step: ${JSON.stringify(step)}`);
+}
+
 /**
  * Parse scripts, detect linear vs DAG mode, and return a topological order.
  * Linear mode (no `needs` on any step) keeps array order.
@@ -81,6 +160,18 @@ export function compileWorkflowScripts(scripts) {
     ids.set(step.id, step.index);
   }
 
+  if (dagMode) {
+    for (const step of steps) {
+      const who = step.id ?? String(step.index);
+      if (step.kind === "set") {
+        throw new Error(`set steps are not allowed in DAG workflows (step ${who})`);
+      }
+      if (step.when) {
+        throw new Error(`when is not allowed in DAG workflows (step ${who})`);
+      }
+    }
+  }
+
   if (!dagMode) {
     return { dagMode: false, steps, order: steps.map((s) => s.index) };
   }
@@ -167,6 +258,56 @@ export function mergeStepData(step, outputsById, triggerData) {
   return data;
 }
 
+/**
+ * @param {object} step
+ * @returns {ParsedSetStep}
+ */
+function parseSetStep(step) {
+  if (step.needs != null) {
+    throw new Error("needs is not allowed on set steps");
+  }
+  const spec = step.set;
+  if (spec == null || typeof spec !== "object" || Array.isArray(spec)) {
+    throw new Error(`Invalid set step: ${JSON.stringify(step)}`);
+  }
+  const expression = spec.expression;
+  const as = spec.as;
+  if (typeof expression !== "string" || !expression.trim()) {
+    throw new Error("set.expression is required");
+  }
+  if (typeof as !== "string" || !AS_IDENT.test(as)) {
+    throw new Error(`Invalid set.as: ${JSON.stringify(as)}`);
+  }
+  if (RESERVED_AS.has(as)) {
+    throw new Error(`set.as "${as}" is reserved`);
+  }
+  compileJsonata(expression, "set.expression");
+  return {
+    kind: "set",
+    script: SET_STEP_SCRIPT,
+    config: { expression, as },
+    expression,
+    as,
+    id: parseOptionalId(step.id),
+    needsKind: "none",
+    needs: [],
+    when: parseWhen(step.when),
+  };
+}
+
+/**
+ * @param {unknown} when
+ * @returns {string | null}
+ */
+function parseWhen(when) {
+  if (when == null || when === "") return null;
+  if (typeof when !== "string") {
+    throw new Error(`Invalid when: ${JSON.stringify(when)}`);
+  }
+  compileJsonata(when, "when");
+  return when;
+}
+
 /**
  * @param {unknown} id
  * @returns {string | null}
@@ -181,7 +322,7 @@ function parseOptionalId(id) {
 
 /**
  * @param {unknown} needs
- * @returns {{ needsKind: ParsedStep["needsKind"], needs: NeedEdge[] }}
+ * @returns {{ needsKind: ParsedScriptStep["needsKind"], needs: NeedEdge[] }}
  */
 function parseNeeds(needs) {
   if (needs == null) {
diff --git a/packages/web/src/lib/format.jsx b/packages/web/src/lib/format.jsx
index 1cd3b04..2462203 100644
--- a/packages/web/src/lib/format.jsx
+++ b/packages/web/src/lib/format.jsx
@@ -13,7 +13,9 @@ export function StatusBadge({ status }) {
         ? "badge-error"
         : status === "running"
           ? "badge-warning"
-          : "badge-ghost";
+          : status === "skipped"
+            ? "badge-info"
+            : "badge-ghost";
   return <span className={`badge badge-sm ${cls}`}>{status ?? "—"}</span>;
 }
 
diff --git a/packages/web/src/lib/workflow-mermaid.js b/packages/web/src/lib/workflow-mermaid.js
index 9876a67..3248d50 100644
--- a/packages/web/src/lib/workflow-mermaid.js
+++ b/packages/web/src/lib/workflow-mermaid.js
@@ -1,12 +1,26 @@
 function parseStep(step) {
   if (typeof step === "string") {
-    return { script: step, id: null, needs: null };
+    return { kind: "script", script: step, id: null, needs: null, when: null, as: null };
+  }
+  if (step?.set) {
+    const as = typeof step.set?.as === "string" && step.set.as ? step.set.as : "set";
+    return {
+      kind: "set",
+      script: null,
+      as,
+      id: typeof step.id === "string" && step.id ? step.id : null,
+      needs: null,
+      when: typeof step.when === "string" && step.when ? step.when : null,
+    };
   }
   if (step?.script) {
     return {
+      kind: "script",
       script: step.script,
+      as: null,
       id: typeof step.id === "string" && step.id ? step.id : null,
       needs: step.needs ?? null,
+      when: typeof step.when === "string" && step.when ? step.when : null,
     };
   }
   return null;
@@ -38,6 +52,15 @@ function triggerLabel(t) {
   return `${method} ${path}`.trim();
 }
 
+function stepLabel(s) {
+  if (s.kind === "set") {
+    const base = s.id ? `${s.id}: set ${s.as}` : `set ${s.as}`;
+    return s.when ? `${base} when: ${s.when}` : base;
+  }
+  const base = s.id ? `${s.id}: ${s.script}` : s.script;
+  return s.when ? `${base} when: ${s.when}` : base;
+}
+
 export function workflowToFlowchart(parsed) {
   /** @type {Record<string, string>} */
   const scriptIds = {};
@@ -72,9 +95,13 @@ export function workflowToFlowchart(parsed) {
   }
 
   for (const s of parsedSteps) {
-    scriptIds[s.mermaidId] = s.script;
-    const label = s.id ? `${s.id}: ${s.script}` : s.script;
-    lines.push(`  ${s.mermaidId}["${mermaidLabel(label)}"]`);
+    const label = mermaidLabel(stepLabel(s));
+    if (s.kind === "set") {
+      lines.push(`  ${s.mermaidId}(["${label}"])`);
+    } else {
+      scriptIds[s.mermaidId] = s.script;
+      lines.push(`  ${s.mermaidId}["${label}"]`);
+    }
   }
 
   if (dagMode) {
diff --git a/packages/web/src/pages/EventDetailPage.jsx b/packages/web/src/pages/EventDetailPage.jsx
index 5537753..9b3bd31 100644
--- a/packages/web/src/pages/EventDetailPage.jsx
+++ b/packages/web/src/pages/EventDetailPage.jsx
@@ -4,6 +4,17 @@ import { useRun } from "../api/hooks.js";
 import { LogViewer } from "../components/LogViewer.jsx";
 import { formatTime, StatusBadge } from "../lib/format.jsx";
 
+function stepLabel(s) {
+  if (s.script === "set") {
+    return s.config?.as ? `set:${s.config.as}` : "set";
+  }
+  return s.script;
+}
+
+function isEditableScript(s) {
+  return Boolean(s.script) && s.script !== "set";
+}
+
 export function EventDetailPage() {
   const { id } = useParams();
   const { data: run, isLoading, error } = useRun(id);
@@ -67,9 +78,13 @@ export function EventDetailPage() {
                 <tr key={s.id}>
                   <td>{s.step_index}</td>
                   <td className="font-mono">
-                    <Link className="link" to={`/scripts/${encodeURIComponent(s.script)}/edit`}>
-                      {s.script}
-                    </Link>
+                    {isEditableScript(s) ? (
+                      <Link className="link" to={`/scripts/${encodeURIComponent(s.script)}/edit`}>
+                        {stepLabel(s)}
+                      </Link>
+                    ) : (
+                      stepLabel(s)
+                    )}
                   </td>
                   <td>
                     <StatusBadge status={s.status} />
diff --git a/packages/web/src/pages/EventsPage.jsx b/packages/web/src/pages/EventsPage.jsx
index fc4e22e..2bb8b15 100644
--- a/packages/web/src/pages/EventsPage.jsx
+++ b/packages/web/src/pages/EventsPage.jsx
@@ -38,6 +38,7 @@ export function EventsPage() {
           <option value="running">running</option>
           <option value="success">success</option>
           <option value="failed">failed</option>
+          <option value="skipped">skipped</option>
         </select>
       </div>
       {isLoading ? (