diff --git a/desktop/scripts/check-file-sizes.mjs b/desktop/scripts/check-file-sizes.mjs
index 778013122..b4f8a9933 100644
--- a/desktop/scripts/check-file-sizes.mjs
+++ b/desktop/scripts/check-file-sizes.mjs
@@ -486,7 +486,9 @@ const overrides = new Map([
   // +2 provider-aware effort: model/provider props threaded to BuzzAgentModelTuningFields.
   // +15 provider/model dropdown fixes: useBakedBuildEnvKeysQuery + hideProviderIds
   // for Databricks v1 gate; prospectiveRuntimeId default fallback for builtins.
-  ["src/features/agents/ui/AgentInstanceEditDialog.tsx", 1180],
+  // +18 PR3 MCP servers UI: mcpServers state, inheritedMcpServers memo,
+  // submit wire, and EditAgentAdvancedFields prop threading.
+  ["src/features/agents/ui/AgentInstanceEditDialog.tsx", 1198],
   // AgentDefinitionDialog grew past 1000 with the following load-bearing fixes:
   // isRuntimeAutoSeededRef tracking for edit-mode seeding (Fizz shows models);
   // runtimeSupportsLlmProviderSelection guard on discovery provider (codex fix);
diff --git a/desktop/src/features/agents/ui/AgentDefinitionDialog.tsx b/desktop/src/features/agents/ui/AgentDefinitionDialog.tsx
index ef7b80354..e2983b3d7 100644
--- a/desktop/src/features/agents/ui/AgentDefinitionDialog.tsx
+++ b/desktop/src/features/agents/ui/AgentDefinitionDialog.tsx
@@ -16,6 +16,7 @@ import { Textarea } from "@/shared/ui/textarea";
 import { AgentCreationPreview } from "./AgentCreationPreview";
 import { PersonaDropdownField } from "./PersonaDropdownField";
 import type { EnvVarsValue } from "./EnvVarsEditor";
+import type { McpServersValue } from "./McpServersEditor";
 import { PersonaAdvancedFields } from "./PersonaAdvancedFields";
 import { PersonaModelField } from "./PersonaModelField";
 import {
@@ -128,6 +129,7 @@ export function AgentDefinitionDialog({
     React.useState(false);
   const [namePoolText, setNamePoolText] = React.useState("");
   const [envVars, setEnvVars] = React.useState<EnvVarsValue>({});
+  const [mcpServers, setMcpServers] = React.useState<McpServersValue>([]);
   const [behaviorDraft, setBehaviorDraft] = React.useState(
     emptyPersonaBehaviorDraft,
   );
@@ -179,14 +181,18 @@ export function AgentDefinitionDialog({
         : "";
     const nextEnvVars =
       "envVars" in initialValues ? (initialValues.envVars ?? {}) : {};
+    const nextMcpServers =
+      "mcpServers" in initialValues ? (initialValues.mcpServers ?? []) : [];
     const nextBehaviorDraft = draftFromBehavior(initialValues.behavior);
     behaviorSeedRef.current = draftFromBehavior(initialValues.behavior);
     setBehaviorDraft(nextBehaviorDraft);
     setNamePoolText(nextNamePoolText);
     setEnvVars(nextEnvVars);
+    setMcpServers(nextMcpServers);
     setShowAdvancedFields(
       nextNamePoolText.trim().length > 0 ||
         Object.keys(nextEnvVars).length > 0 ||
+        nextMcpServers.length > 0 ||
         nextBehaviorDraft.respondTo !== null ||
         nextBehaviorDraft.parallelism.trim().length > 0,
     );
@@ -282,6 +288,7 @@ export function AgentDefinitionDialog({
       provider: providerForSubmit,
       namePool: namePoolInput,
       envVars,
+      mcpServers,
       behavior: behaviorForSubmit(
         behaviorDraft,
         behaviorSeedRef.current,
@@ -867,11 +874,14 @@ export function AgentDefinitionDialog({
                       envVars={envVars}
                       fileSatisfiedEnvKeys={localModeGate.fileSatisfiedEnvKeys}
                       inheritedEnvVars={globalConfig.env_vars}
+                      inheritedMcpServers={globalConfig.mcp_servers}
+                      mcpServers={mcpServers}
                       model={model}
                       modelTuningRuntimeId={runtime}
                       namePoolText={namePoolText}
                       onBehaviorDraftChange={setBehaviorDraft}
                       onEnvVarsChange={setEnvVars}
+                      onMcpServersChange={setMcpServers}
                       onNamePoolTextChange={setNamePoolText}
                       provider={provider}
                       requiredEnvKeys={requiredEnvKeys}
diff --git a/desktop/src/features/agents/ui/AgentInstanceEditDialog.tsx b/desktop/src/features/agents/ui/AgentInstanceEditDialog.tsx
index 52f839431..fe792876b 100644
--- a/desktop/src/features/agents/ui/AgentInstanceEditDialog.tsx
+++ b/desktop/src/features/agents/ui/AgentInstanceEditDialog.tsx
@@ -63,6 +63,11 @@ import {
 } from "./runtimeModelProviderSelection";
 import { AgentCreationPreview } from "./AgentCreationPreview";
 import type { EnvVarsValue } from "./EnvVarsEditor";
+import {
+  mergeMcpServersByName,
+  serversEqual,
+  type McpServersValue,
+} from "./McpServersEditor";
 import { useRequiredCredentialState } from "./useRequiredCredentialState";
 import { CreateAgentRespondToField } from "./RespondToField";
 import { PersonaDropdownField } from "./PersonaDropdownField";
@@ -125,6 +130,9 @@ export function AgentInstanceEditDialog({
   const [isCustomProviderEditing, setIsCustomProviderEditing] =
     React.useState(false);
   const [envVars, setEnvVars] = React.useState<EnvVarsValue>(agent.envVars);
+  const [mcpServers, setMcpServers] = React.useState<McpServersValue>(
+    agent.mcpServers,
+  );
   const [autoRestartOnConfigChange, setAutoRestartOnConfigChange] =
     React.useState(agent.autoRestartOnConfigChange);
   const personasQuery = usePersonasQuery();
@@ -175,6 +183,7 @@ export function AgentInstanceEditDialog({
       setProvider(agent.provider ?? "");
       setIsCustomProviderEditing(false);
       setEnvVars(agent.envVars);
+      setMcpServers(agent.mcpServers);
       setAutoRestartOnConfigChange(agent.autoRestartOnConfigChange);
       setRespondTo(agent.respondTo);
       setRespondToAllowlist(agent.respondToAllowlist);
@@ -424,6 +433,17 @@ export function AgentInstanceEditDialog({
     return { ...globalConfig.env_vars, ...inheritedEnvVars };
   }, [globalConfig.env_vars, inheritedEnvVars]);
 
+  // Merge global + persona MCP servers for the inherited display hint in
+  // McpServersEditor. Persona-layer servers override same-named global ones.
+  const inheritedMcpServers = React.useMemo(
+    () =>
+      mergeMcpServersByName(
+        globalConfig.mcp_servers,
+        linkedPersona?.mcpServers ?? [],
+      ),
+    [globalConfig.mcp_servers, linkedPersona?.mcpServers],
+  );
+
   // Auto-expand Advanced whenever the prospective runtime is buzz-agent so the
   // model-tuning knobs are reachable even when no required key is missing.
   // Fires once per dialog-open cycle; does not re-open if the user manually
@@ -684,6 +704,9 @@ export function AgentInstanceEditDialog({
         envVars: envVarsChanged(submitEnvVars, agent.envVars)
           ? submitEnvVars
           : undefined,
+        mcpServers: serversEqual(mcpServers, agent.mcpServers)
+          ? undefined
+          : mcpServers,
         respondTo: respondTo !== agent.respondTo ? respondTo : undefined,
         // The allowlist is preserved across mode toggles in local UI state
         // (so a user can flip away from allowlist and back without losing
@@ -1081,8 +1104,10 @@ export function AgentInstanceEditDialog({
                           : undefined
                       }
                       inheritedEnvVars={inheritedWithGlobal}
+                      inheritedMcpServers={inheritedMcpServers}
                       inheritHarness={inheritHarness}
                       linkedPersona={linkedPersona}
+                      mcpServers={mcpServers}
                       model={model}
                       modelTuningRuntimeId={prospectiveRuntimeId}
                       parallelism={parallelism}
@@ -1097,6 +1122,7 @@ export function AgentInstanceEditDialog({
                       onAutoRestartChange={setAutoRestartOnConfigChange}
                       onEnvVarsChange={setEnvVars}
                       onInheritHarnessChange={setInheritHarness}
+                      onMcpServersChange={setMcpServers}
                       onParallelismChange={setParallelism}
                       onRelayUrlChange={setRelayUrl}
                       onSystemPromptChange={setSystemPrompt}
diff --git a/desktop/src/features/agents/ui/EditAgentAdvancedFields.tsx b/desktop/src/features/agents/ui/EditAgentAdvancedFields.tsx
index 614c44434..2d75aff10 100644
--- a/desktop/src/features/agents/ui/EditAgentAdvancedFields.tsx
+++ b/desktop/src/features/agents/ui/EditAgentAdvancedFields.tsx
@@ -2,6 +2,7 @@ import { cn } from "@/shared/lib/cn";
 import { Input } from "@/shared/ui/input";
 import { Textarea } from "@/shared/ui/textarea";
 import { EnvVarsEditor, type EnvVarsValue } from "./EnvVarsEditor";
+import { McpServersEditor, type McpServersValue } from "./McpServersEditor";
 import {
   PERSONA_FIELD_CONTROL_CLASS,
   PERSONA_FIELD_SHELL_CLASS,
@@ -21,8 +22,10 @@ export function EditAgentAdvancedFields({
   fileSatisfiedEnvKeys,
   focusKey,
   inheritedEnvVars,
+  inheritedMcpServers = [],
   inheritHarness,
   linkedPersona,
+  mcpServers,
   model,
   modelTuningRuntimeId,
   parallelism,
@@ -36,6 +39,7 @@ export function EditAgentAdvancedFields({
   onAgentCommandChange,
   onEnvVarsChange,
   onInheritHarnessChange,
+  onMcpServersChange,
   onParallelismChange,
   onRelayUrlChange,
   onAutoRestartChange,
@@ -51,7 +55,11 @@ export function EditAgentAdvancedFields({
   /** When set, EnvVarsEditor scrolls and focuses this key's input on mount. */
   focusKey?: string;
   inheritedEnvVars: Record<string, string>;
+  /** Read-only MCP servers inherited from the global + persona layers, merged. */
+  inheritedMcpServers?: McpServersValue;
   inheritHarness: boolean;
+  /** This agent instance's own MCP server layer. */
+  mcpServers: McpServersValue;
   linkedPersona: AgentPersona | null;
   /** Active LLM model — forwarded to BuzzAgentModelTuningFields for effort filtering. */
   model?: string;
@@ -73,6 +81,7 @@ export function EditAgentAdvancedFields({
   onAgentCommandChange: (value: string) => void;
   onEnvVarsChange: (value: EnvVarsValue) => void;
   onInheritHarnessChange: (value: boolean) => void;
+  onMcpServersChange: (value: McpServersValue) => void;
   onParallelismChange: (value: string) => void;
   onRelayUrlChange: (value: string) => void;
   onAutoRestartChange: (value: boolean) => void;
@@ -312,6 +321,17 @@ export function EditAgentAdvancedFields({
         value={envVars}
       />
 
+      {/* MCP servers */}
+      <McpServersEditor
+        disabled={disabled}
+        helperText="Per-instance MCP servers. Override same-named servers from the template and global layers."
+        inheritedLabel="template / global defaults"
+        inheritedServers={inheritedMcpServers}
+        label="MCP servers"
+        onChange={onMcpServersChange}
+        value={mcpServers}
+      />
+
       {/* Tier-1 buzz-agent model-tuning knobs — only shown for buzz-agent. */}
       {isBuzzAgentRuntime(modelTuningRuntimeId) ? (
         <BuzzAgentModelTuningFields
diff --git a/desktop/src/features/agents/ui/GlobalAgentConfigFields.tsx b/desktop/src/features/agents/ui/GlobalAgentConfigFields.tsx
index b84ead485..21f9c09d6 100644
--- a/desktop/src/features/agents/ui/GlobalAgentConfigFields.tsx
+++ b/desktop/src/features/agents/ui/GlobalAgentConfigFields.tsx
@@ -14,6 +14,10 @@ import type {
 } from "@/shared/api/types";
 import { EnvVarsEditor } from "@/features/agents/ui/EnvVarsEditor";
 import type { InheritedEnvRow } from "@/features/agents/ui/EnvVarsEditor";
+import {
+  McpServersEditor,
+  type McpServersValue,
+} from "@/features/agents/ui/McpServersEditor";
 import { getBakedProviderInheritLabel } from "@/features/agents/ui/bakedEnvHelpers";
 import {
   AUTO_PROVIDER_DROPDOWN_VALUE,
@@ -142,6 +146,10 @@ export function GlobalAgentConfigFields({
     onConfigChange({ ...config, model: value || null });
   }
 
+  function handleMcpServersChange(next: McpServersValue) {
+    onConfigChange({ ...config, mcp_servers: next });
+  }
+
   function handleEnvVarsChange(next: Record<string, string>) {
     const effort = config.env_vars[BUZZ_AGENT_THINKING_EFFORT];
     const merged =
@@ -284,6 +292,16 @@ export function GlobalAgentConfigFields({
           )}
         />
       </div>
+
+      {/* MCP servers */}
+      <div className="p-3">
+        <McpServersEditor
+          helperText="Global base layer — applied to all buzz-agent instances. Per-definition and per-instance servers layer on top."
+          label="Global MCP servers"
+          onChange={handleMcpServersChange}
+          value={config.mcp_servers}
+        />
+      </div>
     </SettingsOptionGroup>
   );
 }
diff --git a/desktop/src/features/agents/ui/PersonaAdvancedFields.tsx b/desktop/src/features/agents/ui/PersonaAdvancedFields.tsx
index 113e5e5a7..47a235208 100644
--- a/desktop/src/features/agents/ui/PersonaAdvancedFields.tsx
+++ b/desktop/src/features/agents/ui/PersonaAdvancedFields.tsx
@@ -1,6 +1,7 @@
 import { Input } from "@/shared/ui/input";
 import { cn } from "@/shared/lib/cn";
 import { EnvVarsEditor, type EnvVarsValue } from "./EnvVarsEditor";
+import { McpServersEditor, type McpServersValue } from "./McpServersEditor";
 import { CreateAgentRespondToField } from "./RespondToField";
 import type { PersonaBehaviorDraft } from "./personaBehaviorDraft";
 import { isBuzzAgentRuntime } from "./buzzAgentConfig";
@@ -16,11 +17,14 @@ export function PersonaAdvancedFields({
   disabled,
   envVars,
   inheritedEnvVars = {},
+  mcpServers,
+  inheritedMcpServers = [],
   model,
   modelTuningRuntimeId = "",
   namePoolText,
   onBehaviorDraftChange,
   onEnvVarsChange,
+  onMcpServersChange,
   onNamePoolTextChange,
   provider,
   requiredEnvKeys = [],
@@ -32,6 +36,10 @@ export function PersonaAdvancedFields({
   /** Env vars to display as inherited defaults in tuning-field placeholders.
    *  For templates, pass `globalConfig.env_vars` (the fallback layer). */
   inheritedEnvVars?: EnvVarsValue;
+  /** This definition's local-only MCP server layer. */
+  mcpServers: McpServersValue;
+  /** Read-only servers inherited from the global layer, already merged. */
+  inheritedMcpServers?: McpServersValue;
   /** Active LLM model — forwarded to BuzzAgentModelTuningFields for effort filtering. */
   model?: string;
   /** Runtime id for the buzz-agent tuning knobs visibility gate. */
@@ -39,6 +47,7 @@ export function PersonaAdvancedFields({
   namePoolText: string;
   onBehaviorDraftChange: (value: PersonaBehaviorDraft) => void;
   onEnvVarsChange: (value: EnvVarsValue) => void;
+  onMcpServersChange: (value: McpServersValue) => void;
   onNamePoolTextChange: (value: string) => void;
   /** Active LLM provider id — forwarded to BuzzAgentModelTuningFields for effort filtering. */
   provider?: string;
@@ -144,6 +153,16 @@ export function PersonaAdvancedFields({
         value={envVars}
       />
 
+      <McpServersEditor
+        disabled={disabled}
+        helperText="Local-only MCP servers spawned alongside buzz-agent instances created from this definition."
+        inheritedLabel="global"
+        inheritedServers={inheritedMcpServers}
+        label="MCP servers"
+        onChange={onMcpServersChange}
+        value={mcpServers}
+      />
+
       {/* Tier-1 buzz-agent model-tuning knobs — only shown for buzz-agent. */}
       {isBuzzAgentRuntime(modelTuningRuntimeId) ? (
         <BuzzAgentModelTuningFields