diff --git a/.agents/docs/architecture/testing-strategy.md b/.agents/docs/architecture/testing-strategy.md
index 338fbe34c..9bd600778 100644
--- a/.agents/docs/architecture/testing-strategy.md
+++ b/.agents/docs/architecture/testing-strategy.md
@@ -180,7 +180,8 @@ coverage is therefore a smoke subset, not the full suite.
 
 `webServer` boots `apps/api`, `apps/gateway` and `apps/web` by running each app's own `pnpm dev:test`
 with `NODE_ENV=test`, which is what gives the API an in-memory Mongo replica set instead of an
-external database. `workers: 1` on CI; `fullyParallel` otherwise. The default assertion timeout is
+external database. `workers: 1` on CI and 2 elsewhere, with `fullyParallel` on (`testing/AGENTS.md`
+§Running has why, and the override). The default assertion timeout is
 raised to 15s because a 2-core runner doing real DB work misses the 5s default.
 
 ## Known warts
diff --git a/.env.template b/.env.template
index 1b8924cca..4d9984798 100644
--- a/.env.template
+++ b/.env.template
@@ -122,6 +122,8 @@ PLAYGROUND_DEV_SERVER_PORT=3750
 GATEWAY_DEV_SERVER_PORT=3500
 # The port to use for the Vite (full web app) development server
 WEB_DEV_SERVER_PORT=3000
+# The number of end-to-end tests to run in parallel (default: 2, or 1 when CI is set)
+E2E_WORKERS=
 # Set an arbitrary delay (in milliseconds) for all responses (useful for testing suspense)
 API_RESPONSE_DELAY=
 # If set to 'true' and NODE_ENV === 'development', then login is automated
diff --git a/testing/AGENTS.md b/testing/AGENTS.md
index acbbf9387..2cea8293e 100644
--- a/testing/AGENTS.md
+++ b/testing/AGENTS.md
@@ -112,6 +112,14 @@ preview is an iframe on the other loopback name, so the spec drives it through a
 is served from the root of the API, and its Redoc page requests `/spec.json`, which the web origin's
 `/api` proxy does not route.
 
+**The suite runs on two workers, and one on CI.** Playwright's own default of half the cores logs in
+faster than the API's login throttle allows (50 a minute), so tests partway through the suite fail
+with `Login failed … (429)`, and each failure restarts a worker that logs in again. Set `E2E_WORKERS`
+in the root `.env` to change the count; `src/support/env.ts` reads it and throws on anything but a
+positive integer. A shell export loses to `.env` wherever `.env` carries the key, blank included: the
+`test:*` scripts load it through `env-cmd`, whose values win, and `.env.template` carries the key
+blank. For one run, pass `--workers=<n>` after the script instead.
+
 Projects: `setup` (with `teardown` attached), `chromium` (every spec), and `firefox`, which greps
 `/@smoke/`. **Cross-browser coverage exists only for tests whose title contains `@smoke`** — add the
 tag to a critical flow, leave it off everything else.
diff --git a/testing/playwright.config.ts b/testing/playwright.config.ts
index cf144e0aa..c1fb7a024 100644
--- a/testing/playwright.config.ts
+++ b/testing/playwright.config.ts
@@ -2,7 +2,7 @@ import * as path from 'node:path';
 
 import { defineConfig, devices } from '@playwright/test';
 
-import { apiPort, baseURL, gatewayPort, playgroundPort, webPort } from './src/support/env';
+import { apiPort, baseURL, gatewayPort, playgroundPort, webPort, workerCount } from './src/support/env';
 
 const webServerDefaults = {
   gracefulShutdown: { signal: 'SIGINT', timeout: 1000 },
@@ -65,5 +65,7 @@ export default defineConfig({
       url: `http://localhost:${playgroundPort}`
     }
   ],
-  workers: process.env.CI ? 1 : undefined
+  // Playwright's own default is half the cores. That many workers log in faster than the API's login
+  // throttle allows partway through the suite, and leave a developer's machine little for anything else.
+  workers: workerCount ?? (process.env.CI ? 1 : 2)
 });
diff --git a/testing/src/support/env.ts b/testing/src/support/env.ts
index 53308cc7e..5ef3dfb54 100644
--- a/testing/src/support/env.ts
+++ b/testing/src/support/env.ts
@@ -16,6 +16,18 @@ function requiredNumber(name: string): number {
   return value;
 }
 
+function optionalPositiveInteger(name: string): number | undefined {
+  const raw = process.env[name];
+  if (!raw) {
+    return undefined;
+  }
+  const value = parseNumber(raw);
+  if (!Number.isInteger(value) || value < 1) {
+    throw new Error(`Expected ${name} to be a positive integer, got ${raw}`);
+  }
+  return value;
+}
+
 // Read straight from the same `.env` apps/web builds `config.meta.contactEmail` from: a developer's
 // value differs from the `.env.template` one CI generates, so a literal here only passes locally.
 export const contactEmail = required('CONTACT_EMAIL');
@@ -25,6 +37,9 @@ export const gatewayPort = requiredNumber('GATEWAY_DEV_SERVER_PORT');
 export const playgroundPort = requiredNumber('PLAYGROUND_DEV_SERVER_PORT');
 export const webPort = requiredNumber('WEB_DEV_SERVER_PORT');
 
+/** How many tests run at once, where `.env` says; `playwright.config.ts` holds the default. */
+export const workerCount = optionalPositiveInteger('E2E_WORKERS');
+
 /** How often, in milliseconds, the API pulls completed assignments from the gateway. */
 export const gatewayRefreshInterval = requiredNumber('GATEWAY_REFRESH_INTERVAL');