diff --git a/EXTERNAL_WP_CLI_TESTING_SETUP.md b/EXTERNAL_WP_CLI_TESTING_SETUP.md
new file mode 100644
index 0000000..af54717
--- /dev/null
+++ b/EXTERNAL_WP_CLI_TESTING_SETUP.md
@@ -0,0 +1,103 @@
+# External WP-CLI Testing Setup
+
+This guide explains how to enable and run External WP-CLI Testing from the Builder, with tools loaded into OpenCode only when the feature toggle is enabled.
+
+## What This Adds
+
+- A gated MCP tool named `test_plugin_external_wp` (plus a helper tool `external_wp_testing_config`).
+- Tools are injected into OpenCode only when the Builder toggle is on.
+- All connection/auth settings are controlled via environment variables.
+
+## Prerequisites
+
+1. A reachable WordPress host with WP-CLI installed.
+2. SSH access to that host from the server running the chat app.
+3. The SSH user must be able to run WP-CLI at the configured path.
+
+## Required Environment Variables
+
+Set these in the environment where the chat server runs (the same process that launches OpenCode).
+
+- `TEST_WP_HOST` (or `EXTERNAL_WP_HOST`)
+  - Hostname or IP of the WordPress server.
+- `TEST_WP_SSH_USER` (or `EXTERNAL_WP_SSH_USER`)
+  - SSH username for the WordPress server.
+- `TEST_WP_SSH_KEY` (or `TEST_WP_SSH_KEY_PATH`, or `EXTERNAL_WP_SSH_KEY`)
+  - Path to the SSH private key file.
+
+If these are missing, the tool will return a clear error.
+
+## Optional Environment Variables
+
+- `TEST_WP_PATH` (or `EXTERNAL_WP_PATH`)
+  - Default: `/var/www/html`
+  - Path to the WordPress root on the remote host.
+- `TEST_WP_BASE_URL` (or `EXTERNAL_WP_BASE_URL`)
+  - Default: `https://<TEST_WP_HOST>`
+  - Base URL for the site.
+- `TEST_WP_MULTISITE` (or `EXTERNAL_WP_MULTISITE`)
+  - Default: `true`
+  - Enables multisite subsite isolation.
+- `TEST_WP_SUBSITE_PREFIX` (or `EXTERNAL_WP_SUBSITE_PREFIX`)
+  - Default: `test`
+  - Prefix for created subsites.
+- `TEST_WP_SUBSITE_DOMAIN` (or `EXTERNAL_WP_SUBSITE_DOMAIN`)
+  - Default: empty (falls back to host)
+  - Domain used when subsite mode is subdomain.
+- `TEST_WP_SUBSITE_MODE` (or `EXTERNAL_WP_SUBSITE_MODE`)
+  - Default: `subdirectory`
+  - Allowed values: `subdirectory`, `subdomain`.
+- `TEST_WP_ERROR_LOG` (or `EXTERNAL_WP_ERROR_LOG`)
+  - Default: `/var/log/wp-errors.log`
+  - Used by the default "Scan error log" scenario.
+- `TEST_SSH_STRICT` (or `EXTERNAL_WP_SSH_STRICT`)
+  - Default: `false`
+  - When `true`, enforces strict host key checking.
+- `TEST_MAX_CONCURRENT` (or `EXTERNAL_WP_MAX_CONCURRENT`)
+  - Default: `20`
+  - Max concurrent tests.
+- `TEST_QUEUE_TIMEOUT` (or `EXTERNAL_WP_QUEUE_TIMEOUT`)
+  - Default: `300000` (ms)
+- `TEST_TIMEOUT` (or `EXTERNAL_WP_TEST_TIMEOUT`)
+  - Default: `600000` (ms)
+- `TEST_AUTO_CLEANUP` (or `EXTERNAL_WP_AUTO_CLEANUP`)
+  - Default: `true`
+  - Cleans up subsites after tests complete.
+- `TEST_CLEANUP_DELAY` (or `EXTERNAL_WP_CLEANUP_DELAY`)
+  - Default: `3600000` (ms)
+
+## Example .env
+
+TEST_WP_HOST=wp-test.example.com
+TEST_WP_SSH_USER=wordpress
+TEST_WP_SSH_KEY=C:\\keys\\wp-test.pem
+TEST_WP_PATH=/var/www/html
+TEST_WP_BASE_URL=https://wp-test.example.com
+TEST_WP_MULTISITE=true
+TEST_WP_SUBSITE_MODE=subdirectory
+TEST_WP_SUBSITE_PREFIX=test
+TEST_WP_ERROR_LOG=/var/log/wp-errors.log
+TEST_SSH_STRICT=false
+TEST_MAX_CONCURRENT=20
+TEST_TIMEOUT=600000
+
+## Builder Toggle Behavior
+
+- Open the Builder and enable the "External WP CLI testing" toggle.
+- When enabled, the chat server injects the MCP server definition via `OPENCODE_EXTRA_MCP_SERVERS`.
+- When disabled, the environment variable is removed before OpenCode is spawned, so the tools are not exposed.
+
+## Running a Test
+
+1. Enable the toggle in Builder.
+2. Proceed with the build or let the AI call `test_plugin_external_wp`.
+3. The tool runs WP-CLI commands over SSH and returns a JSON report.
+
+## Quick Sanity Check Tool
+
+You can ask the AI to call `external_wp_testing_config` to validate your settings. It returns the resolved config and a list of missing required variables.
+
+## Notes
+
+- `test_plugin_external_wp` only supports `test_mode=cli` in the current implementation.
+- Ensure the SSH user can execute WP-CLI and write to the plugin directory.
diff --git a/chat/public/builder.js b/chat/public/builder.js
index 33b7173..6930800 100644
--- a/chat/public/builder.js
+++ b/chat/public/builder.js
@@ -3964,6 +3964,7 @@ async function sendMessage() {
       model,
       cli,
       attachments: pendingAttachments.length ? pendingAttachments : undefined,
+      externalTestingEnabled: !!builderState.externalTestingEnabled // Send feature toggle state to server
     };
     // Preserve opencodeSessionId to continue in the same session
     if (currentSession && currentSession.opencodeSessionId) {
diff --git a/chat/server.js b/chat/server.js
index 3986d19..fcefa49 100644
--- a/chat/server.js
+++ b/chat/server.js
@@ -8800,6 +8800,14 @@ async function sendToOpencode({ session, model, content, message, cli, streamCal
     args.push('--session', opencodeSessionId);
   }
 
+  // Configure WP CLI Testing MCP server if feature is enabled
+  const wpCliMcpEnabled = message?.externalTestingEnabled === true;
+  log('WP CLI Testing MCP server configuration', { 
+    enabled: wpCliMcpEnabled, 
+    messageId: message?.id,
+    sessionId: session.id 
+  });
+
   // Ensure content is properly passed as the final argument
   if (typeof clean !== 'string' || clean.length === 0) {
     throw new Error('Message content is invalid or empty after sanitization');
@@ -8866,6 +8874,36 @@ async function sendToOpencode({ session, model, content, message, cli, streamCal
 
     // Use the OpenCode process manager for execution
     // This ensures all sessions share the same OpenCode instance when possible
+    
+    // Build environment variables including WP CLI MCP server config
+    const executionEnv = {
+      ...process.env,
+      OPENAI_API_KEY: OPENCODE_OLLAMA_API_KEY
+    };
+    
+    // Add WP CLI Testing MCP server to OpenCode config if enabled
+    if (wpCliMcpEnabled) {
+      const wpMcpServerPath = path.resolve(__dirname, '../opencode/mcp-servers/wp-cli-testing/index.js');
+      log('Enabling WP CLI Testing MCP server', { path: wpMcpServerPath, messageId: message?.id });
+      
+      // Configure OpenCode to include the WP CLI testing MCP server
+      // We pass this via environment variable that OpenCode can read
+      executionEnv.OPENCODE_EXTRA_MCP_SERVERS = JSON.stringify([
+        {
+          name: 'wp-cli-testing',
+          command: 'node',
+          args: [wpMcpServerPath],
+          disabled: false
+        }
+      ]);
+    } else {
+      // Safety: ensure the tools are not injected when the builder toggle is off,
+      // even if the parent process environment happens to have the variable set.
+      if (executionEnv.OPENCODE_EXTRA_MCP_SERVERS) {
+        delete executionEnv.OPENCODE_EXTRA_MCP_SERVERS;
+      }
+    }
+    
     const { stdout, stderr } = await opencodeManager.executeInSession(
       session?.id || 'standalone',
       workspaceDir,
@@ -8873,10 +8911,7 @@ async function sendToOpencode({ session, model, content, message, cli, streamCal
       args,
       {
         timeout: 600000, // 10 minute timeout to prevent stuck processes
-        env: {
-          ...process.env,
-          OPENAI_API_KEY: OPENCODE_OLLAMA_API_KEY
-        },
+        env: executionEnv,
         onData: (type, chunk) => {
         try {
           const now = Date.now();
diff --git a/opencode/mcp-servers/wp-cli-testing/index.js b/opencode/mcp-servers/wp-cli-testing/index.js
new file mode 100644
index 0000000..d5195e8
--- /dev/null
+++ b/opencode/mcp-servers/wp-cli-testing/index.js
@@ -0,0 +1,274 @@
+import { Server } from "@modelcontextprotocol/sdk/server/index.js"
+import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js"
+import {
+  CallToolRequestSchema,
+  ListToolsRequestSchema,
+} from "@modelcontextprotocol/sdk/types.js"
+import { z } from "zod"
+
+// This MCP server wraps the existing external WP testing implementation used by the chat app.
+// It is intentionally kept small and env-configurable so host apps can load it only when needed.
+
+const ToolInput = {
+  plugin_path: z.string().min(1),
+  plugin_slug: z.string().optional(),
+  session_id: z.string().optional(),
+  test_mode: z.enum(["cli", "visual", "both"]).optional().default("cli"),
+  required_plugins: z
+    .array(
+      z.object({
+        plugin_slug: z.string().min(1),
+        source: z.enum(["wordpress.org", "url", "local"]).optional(),
+        source_url: z.string().optional(),
+        activate: z.boolean().optional(),
+      }),
+    )
+    .optional(),
+  test_scenarios: z
+    .array(
+      z.object({
+        name: z.string().optional(),
+        type: z.string().optional(),
+        url: z.string().optional(),
+        selector: z.string().optional(),
+        expected_text: z.string().optional(),
+        wp_cli_command: z.string().optional(),
+        shortcode: z.string().optional(),
+        hook: z.string().optional(),
+        ajax_action: z.string().optional(),
+        method: z.string().optional(),
+        body: z.string().optional(),
+        assertions: z
+          .object({
+            status_code: z.number().optional(),
+            contains: z.array(z.string()).optional(),
+            not_contains: z.array(z.string()).optional(),
+            wp_cli_success: z.boolean().optional(),
+          })
+          .optional(),
+      }),
+    )
+    .optional(),
+  config_overrides: z.record(z.any()).optional(),
+}
+
+function toJsonSchema(schema) {
+  // zod v4 exposes toJSONSchema under z.* in OpenCode, but in plain node usage
+  // we keep schema definitions explicit below for MCP.
+  // This helper exists only for future extension.
+  void schema
+  return {
+    type: "object",
+    additionalProperties: false,
+  }
+}
+
+const TestToolInputJsonSchema = {
+  type: "object",
+  additionalProperties: false,
+  required: ["plugin_path"],
+  properties: {
+    plugin_path: { type: "string", description: "Local filesystem path to plugin root" },
+    plugin_slug: { type: "string", description: "Plugin slug (defaults to folder name)" },
+    session_id: { type: "string", description: "Optional session id for isolation" },
+    test_mode: {
+      type: "string",
+      enum: ["cli", "visual", "both"],
+      description: "Testing mode (only 'cli' is implemented in this server)",
+    },
+    required_plugins: {
+      type: "array",
+      description: "Plugins to install/activate before running scenarios",
+      items: {
+        type: "object",
+        additionalProperties: false,
+        required: ["plugin_slug"],
+        properties: {
+          plugin_slug: { type: "string" },
+          source: { type: "string", enum: ["wordpress.org", "url", "local"] },
+          source_url: { type: "string" },
+          activate: { type: "boolean" },
+        },
+      },
+    },
+    test_scenarios: {
+      type: "array",
+      description: "Scenario list; if omitted, defaults are generated",
+      items: {
+        type: "object",
+        additionalProperties: true,
+      },
+    },
+    config_overrides: {
+      type: "object",
+      description: "Overrides for external WP testing configuration (see docs/env vars)",
+      additionalProperties: true,
+    },
+  },
+}
+
+const server = new Server(
+  {
+    name: "wp-cli-testing",
+    version: "1.0.0",
+  },
+  {
+    capabilities: {
+      tools: {},
+    },
+  },
+)
+
+server.setRequestHandler(ListToolsRequestSchema, async () => {
+  return {
+    tools: [
+      {
+        name: "test_plugin_external_wp",
+        description:
+          "Run WP-CLI based verification against an externally hosted WordPress test site (over SSH).",
+        inputSchema: TestToolInputJsonSchema,
+      },
+      {
+        name: "external_wp_testing_config",
+        description:
+          "Return the resolved external WP testing config (from env vars) and highlight missing/invalid settings.",
+        inputSchema: {
+          type: "object",
+          additionalProperties: false,
+          properties: {
+            config_overrides: {
+              type: "object",
+              additionalProperties: true,
+              description: "Optional config overrides merged on top of env defaults",
+            },
+          },
+        },
+      },
+    ],
+  }
+})
+
+server.setRequestHandler(CallToolRequestSchema, async (req) => {
+  const toolName = req.params.name
+  const args = (req.params.arguments ?? {})
+
+  // Lazy-load to avoid paying cost unless tool is actually invoked.
+  // Note: external-wp-testing.js is CommonJS; import default gives module.exports.
+  const externalTesting = await import("../../../chat/external-wp-testing.js")
+  const mod = externalTesting.default ?? externalTesting
+  const createExternalWpTester = mod?.createExternalWpTester
+  const getExternalTestingConfig = mod?.getExternalTestingConfig
+
+  if (typeof createExternalWpTester !== "function" || typeof getExternalTestingConfig !== "function") {
+    return {
+      content: [
+        {
+          type: "text",
+          text:
+            "wp-cli-testing MCP server misconfigured: could not load chat/external-wp-testing.js exports.",
+        },
+      ],
+      isError: true,
+    }
+  }
+
+  if (toolName === "external_wp_testing_config") {
+    const overrides =
+      args && typeof args === "object" && (args.config_overrides && typeof args.config_overrides === "object")
+        ? args.config_overrides
+        : {}
+
+    const config = getExternalTestingConfig(overrides)
+    const missing = []
+    if (!config.wpHost) missing.push("TEST_WP_HOST (or EXTERNAL_WP_HOST)")
+    if (!config.wpSshUser) missing.push("TEST_WP_SSH_USER (or EXTERNAL_WP_SSH_USER)")
+    if (!config.wpSshKey) missing.push("TEST_WP_SSH_KEY (or EXTERNAL_WP_SSH_KEY)")
+
+    const safeConfig = {
+      ...config,
+      // avoid leaking filesystem layout too much; keep key path but don’t include any private key contents.
+      wpSshKey: config.wpSshKey,
+    }
+
+    return {
+      content: [
+        {
+          type: "text",
+          text: JSON.stringify(
+            {
+              ok: missing.length === 0,
+              missing,
+              config: safeConfig,
+            },
+            null,
+            2,
+          ),
+        },
+      ],
+    }
+  }
+
+  if (toolName === "test_plugin_external_wp") {
+    const parsed = z
+      .object(ToolInput)
+      .safeParse(args && typeof args === "object" ? args : {})
+
+    if (!parsed.success) {
+      return {
+        content: [{ type: "text", text: JSON.stringify({ ok: false, error: parsed.error.message }, null, 2) }],
+        isError: true,
+      }
+    }
+
+    if (parsed.data.test_mode !== "cli") {
+      return {
+        content: [
+          {
+            type: "text",
+            text: JSON.stringify(
+              {
+                ok: false,
+                error:
+                  "Only test_mode='cli' is implemented by this MCP server. Use cli mode or extend the server.",
+              },
+              null,
+              2,
+            ),
+          },
+        ],
+        isError: true,
+      }
+    }
+
+    const tester = createExternalWpTester({})
+
+    const result = await tester.runTest(
+      {
+        plugin_path: parsed.data.plugin_path,
+        plugin_slug: parsed.data.plugin_slug,
+        session_id: parsed.data.session_id,
+        required_plugins: parsed.data.required_plugins ?? [],
+        test_scenarios: parsed.data.test_scenarios ?? [],
+        test_mode: "cli",
+      },
+      {
+        configOverrides:
+          parsed.data.config_overrides && typeof parsed.data.config_overrides === "object"
+            ? parsed.data.config_overrides
+            : {},
+      },
+    )
+
+    return {
+      content: [{ type: "text", text: JSON.stringify(result, null, 2) }],
+    }
+  }
+
+  return {
+    content: [{ type: "text", text: `Unknown tool: ${toolName}` }],
+    isError: true,
+  }
+})
+
+const transport = new StdioServerTransport()
+await server.connect(transport)
diff --git a/opencode/packages/opencode/src/config/config.ts b/opencode/packages/opencode/src/config/config.ts
index a231a53..055b4d6 100644
--- a/opencode/packages/opencode/src/config/config.ts
+++ b/opencode/packages/opencode/src/config/config.ts
@@ -235,6 +235,69 @@ export namespace Config {
       result.compaction = { ...result.compaction, prune: false }
     }
 
+    // Allow host applications to inject additional MCP servers at runtime.
+    // This is intentionally env-driven so tools can be loaded only when needed
+    // (e.g. a Builder feature toggle) without requiring writing config files.
+    const extraMcpRaw = process.env.OPENCODE_EXTRA_MCP_SERVERS
+    if (extraMcpRaw && typeof extraMcpRaw === "string") {
+      try {
+        const parsed = JSON.parse(extraMcpRaw)
+        if (Array.isArray(parsed)) {
+          result.mcp ??= {}
+          for (const entry of parsed) {
+            if (!entry || typeof entry !== "object") continue
+            const name = typeof (entry as any).name === "string" ? (entry as any).name.trim() : ""
+            if (!name) continue
+
+            const enabledFromEntry = (entry as any).enabled
+            const disabledFromEntry = (entry as any).disabled
+            const enabled =
+              typeof enabledFromEntry === "boolean"
+                ? enabledFromEntry
+                : typeof disabledFromEntry === "boolean"
+                  ? !disabledFromEntry
+                  : true
+
+            const env = (entry as any).env
+            const envRecord: Record<string, string> | undefined =
+              env && typeof env === "object" && !Array.isArray(env) ? (env as Record<string, string>) : undefined
+
+            const timeout = (entry as any).timeout
+            const timeoutMs = Number.isFinite(timeout) ? Math.max(0, Number(timeout)) : undefined
+
+            // Accept either { command: 'node', args: [...] } or { command: ['node', ...] }
+            const commandVal = (entry as any).command
+            const argsVal = (entry as any).args
+
+            const commandParts: string[] = Array.isArray(commandVal)
+              ? commandVal.filter((x: any) => typeof x === "string" && x.length)
+              : typeof commandVal === "string" && commandVal.trim().length
+                ? [commandVal.trim()]
+                : []
+
+            const argsParts: string[] = Array.isArray(argsVal) ? argsVal.filter((x: any) => typeof x === "string") : []
+
+            if (commandParts.length === 0) {
+              log.warn("Ignoring OPENCODE_EXTRA_MCP_SERVERS entry without command", { name })
+              continue
+            }
+
+            result.mcp[name] = {
+              type: "local",
+              command: [...commandParts, ...argsParts],
+              env: envRecord,
+              enabled,
+              ...(timeoutMs !== undefined ? { timeout: timeoutMs } : {}),
+            }
+          }
+        } else {
+          log.warn("OPENCODE_EXTRA_MCP_SERVERS must be a JSON array; ignoring", { valueType: typeof parsed })
+        }
+      } catch (err) {
+        log.warn("Failed to parse OPENCODE_EXTRA_MCP_SERVERS; ignoring", { error: err instanceof Error ? err.message : String(err) })
+      }
+    }
+
     result.plugin = deduplicatePlugins(result.plugin ?? [])
 
     return {