diff --git a/docs/swarm/ui.md b/docs/swarm/ui.md
index 0bf00d7d..038efc3b 100644
--- a/docs/swarm/ui.md
+++ b/docs/swarm/ui.md
@@ -386,6 +386,19 @@ controller puts back what it replaced. Each agent name keys its settings and
 destroying an agent doesn't clear them, so a name set up before keeps its
 stored settings when you leave the fields empty.
 
+### Initial AGENTS.md at creation
+
+A third collapsed section, **instructions**, holds a plain text box for the
+text the new agent's `AGENTS.md` starts with. Left empty, or holding only
+whitespace, it sends nothing and the agent starts without the file. Otherwise
+the text goes as typed in the optional `agents_md` field of `POST /api/agents`.
+The agent writes it on its first start, and only when it has no `AGENTS.md`
+yet, so creating an agent again under a name that has one never replaces it.
+The controller refuses a text over 64 KiB; its reason shows under the box and
+no agent is created. After a successful create the box empties. The
+[instructions editor](#editing-an-agents-instructions) changes the file later.
+The [swarm README](README.md#an-agents-agentsmd) has the wire details.
+
 ### Linking external accounts
 
 Each agent on `/agents` opens three dialogs that write a credential for it
diff --git a/frontend/packages/swarm-ui/src/pages/CreateAgentAgentsMd.ts b/frontend/packages/swarm-ui/src/pages/CreateAgentAgentsMd.ts
new file mode 100644
index 00000000..94c4c04e
--- /dev/null
+++ b/frontend/packages/swarm-ui/src/pages/CreateAgentAgentsMd.ts
@@ -0,0 +1,23 @@
+// The create-agent form's initial `AGENTS.md` field, kept out of the
+// component so `npm test` can run it.
+import type { ProblemDetails } from "@hive/shared/api-error.js";
+
+/**
+ * The `agents_md` to send with a create: nothing while the box is empty or
+ * holds only whitespace, so the agent starts without the file; otherwise the
+ * text as typed.
+ */
+export function agentsMdBody(text: string): { agents_md?: string } {
+  return text.trim() === "" ? {} : { agents_md: text };
+}
+
+/**
+ * The controller's refusal of the text, when `problem` is one: a 400 whose
+ * detail starts with the field's name. It shows beside the box, so any other
+ * failure stays with the form's general error.
+ */
+export function agentsMdRefusal(problem: ProblemDetails): string | null {
+  return problem.status === 400 && problem.detail?.startsWith("agents_md ")
+    ? problem.detail
+    : null;
+}
diff --git a/frontend/packages/swarm-ui/src/pages/CreateAgentForm.css b/frontend/packages/swarm-ui/src/pages/CreateAgentForm.css
index e6e2ac3a..5e131ef1 100644
--- a/frontend/packages/swarm-ui/src/pages/CreateAgentForm.css
+++ b/frontend/packages/swarm-ui/src/pages/CreateAgentForm.css
@@ -69,6 +69,11 @@
 .create-agent-result-ok {
   color: var(--green);
 }
+/* The controller's refusal of the AGENTS.md text, under its box. */
+.create-agent-field-error {
+  margin: 0;
+  color: var(--red);
+}
 /* The picked archetype's description, under its select. */
 .create-agent-archetype-description {
   margin: 0;
diff --git a/frontend/packages/swarm-ui/src/pages/CreateAgentForm.tsx b/frontend/packages/swarm-ui/src/pages/CreateAgentForm.tsx
index 3074c765..d27bbd8d 100644
--- a/frontend/packages/swarm-ui/src/pages/CreateAgentForm.tsx
+++ b/frontend/packages/swarm-ui/src/pages/CreateAgentForm.tsx
@@ -38,6 +38,7 @@ import {
   SelectField,
   type SelectOption,
 } from "../ui/select-field/SelectField.js";
+import { TextAreaField } from "../ui/text-area-field/TextAreaField.js";
 import { Button } from "../ui/button/Button.js";
 import { capsBody, LimitsFields } from "../agent/detail/AgentLimits.js";
 import {
@@ -60,6 +61,7 @@ import {
   requestArchetype,
   type ArchetypeList,
 } from "./CreateAgentArchetype.js";
+import { agentsMdBody, agentsMdRefusal } from "./CreateAgentAgentsMd.js";
 import "./CreateAgentForm.css";
 
 // Mirrors swarm-controller's `HiveEntry` — same shape `HivesPage`
@@ -144,6 +146,8 @@ export function CreateAgentForm({
     null,
   );
   const [archetype, setArchetype] = useState("");
+  // The text the agent's `AGENTS.md` starts with; empty sends none.
+  const [agentsMd, setAgentsMd] = useState("");
   const picked = archetypes?.archetypes.find(
     (a) => archetypeKey(a) === archetype,
   );
@@ -211,6 +215,9 @@ export function CreateAgentForm({
     label: h.name,
   }));
   const hivesReady = hives !== null && hives.length > 0;
+  // The controller's size refusal of the AGENTS.md text, shown by its box.
+  const refusal =
+    result.status === "error" ? agentsMdRefusal(result.problem) : null;
 
   async function submit(e: Event) {
     e.preventDefault();
@@ -232,6 +239,7 @@ export function CreateAgentForm({
             ? requestPermissions(selected, catalogue.default)
             : undefined,
           archetype: requestArchetype(picked),
+          ...agentsMdBody(agentsMd),
         }),
       });
       if (!r.ok) {
@@ -241,6 +249,7 @@ export function CreateAgentForm({
       const data = (await r.json()) as CreateAgentResponse;
       setResult({ status: "done", nodeId: data.node_id });
       setName("");
+      setAgentsMd("");
       pickArchetype("");
       if (catalogue)
         setSelected(
@@ -258,8 +267,8 @@ export function CreateAgentForm({
           <p class="create-agent-intro">
             Create a new agent's swarm-level identity. This only queues the job
             — check <Link href="/jobs">jobs</Link> to watch it settle. Resource
-            caps and inference are optional; leave them empty to set nothing. A
-            name set up before keeps the settings stored for it.
+            caps, inference and instructions are optional; leave them empty to
+            set nothing. A name set up before keeps the settings stored for it.
           </p>
           {hivesError && (
             <ApiErrorPanel
@@ -365,6 +374,22 @@ export function CreateAgentForm({
                 />
               </div>
             </details>
+            <details class="create-agent-section">
+              <summary>instructions</summary>
+              <div class="create-agent-section-body">
+                <TextAreaField
+                  id="agent-agents-md"
+                  label="AGENTS.md"
+                  value={agentsMd}
+                  rows={8}
+                  placeholder="the text the agent's AGENTS.md starts with; leave empty for none"
+                  onInput={setAgentsMd}
+                />
+                {refusal !== null && (
+                  <p class="create-agent-field-error">{refusal}</p>
+                )}
+              </div>
+            </details>
             <Button
               variant="primary"
               type="submit"
@@ -384,7 +409,7 @@ export function CreateAgentForm({
               <Link href="/jobs">watch it in jobs</Link>
             </p>
           )}
-          {result.status === "error" && (
+          {result.status === "error" && refusal === null && (
             <ApiErrorPanel context="failed to queue" problem={result.problem} />
           )}
         </Panel>
diff --git a/frontend/packages/swarm-ui/test/create-agents-md.test.mjs b/frontend/packages/swarm-ui/test/create-agents-md.test.mjs
new file mode 100644
index 00000000..1edc8218
--- /dev/null
+++ b/frontend/packages/swarm-ui/test/create-agents-md.test.mjs
@@ -0,0 +1,43 @@
+// What the create-agent form sends for the initial AGENTS.md, and which error
+// it shows beside the box. Run by `npm test`, which Node runs with its
+// built-in test runner and type stripping, so the `.ts` module is imported as
+// it is.
+import assert from "node:assert/strict";
+import { test } from "node:test";
+import {
+  agentsMdBody,
+  agentsMdRefusal,
+} from "../src/pages/CreateAgentAgentsMd.ts";
+
+test("an empty or whitespace-only box sends no agents_md", () => {
+  assert.deepEqual(agentsMdBody(""), {});
+  assert.deepEqual(agentsMdBody("  \n\t \n"), {});
+});
+
+test("text is sent as typed, whitespace and all", () => {
+  assert.deepEqual(agentsMdBody("# me\n\nDo the thing.\n"), {
+    agents_md: "# me\n\nDo the thing.\n",
+  });
+  assert.deepEqual(agentsMdBody("  indented"), { agents_md: "  indented" });
+});
+
+test("the size refusal shows beside the box", () => {
+  const detail = "agents_md is 70000 bytes; the limit is 65536";
+  assert.equal(agentsMdRefusal({ status: 400, detail }), detail);
+});
+
+test("other failures stay with the general error", () => {
+  assert.equal(
+    agentsMdRefusal({ status: 400, detail: "name is not a valid identifier" }),
+    null,
+  );
+  assert.equal(
+    agentsMdRefusal({
+      status: 500,
+      detail: "agents_md is 70000 bytes; the limit is 65536",
+    }),
+    null,
+  );
+  assert.equal(agentsMdRefusal({ status: 400 }), null);
+  assert.equal(agentsMdRefusal({ detail: "agents_md is too long" }), null);
+});