diff --git a/backend/routers/admin.py b/backend/routers/admin.py
new file mode 100644
index 0000000..61b1a0a
--- /dev/null
+++ b/backend/routers/admin.py
@@ -0,0 +1,23 @@
+"""Admin router — system settings and stats."""
+
+from fastapi import APIRouter, Response
+
+router = APIRouter()
+
+
+@router.get("/settings", status_code=501)
+def get_settings():
+    """System settings (guest access, default model, etc.)."""
+    return Response(status_code=501, content="Not Implemented")
+
+
+@router.put("/settings", status_code=501)
+def update_settings():
+    """Update settings."""
+    return Response(status_code=501, content="Not Implemented")
+
+
+@router.get("/stats", status_code=501)
+def get_stats():
+    """System-wide stats (total runs, cache hit rate, etc.)."""
+    return Response(status_code=501, content="Not Implemented")
diff --git a/backend/routers/auth.py b/backend/routers/auth.py
new file mode 100644
index 0000000..126994d
--- /dev/null
+++ b/backend/routers/auth.py
@@ -0,0 +1,23 @@
+"""Auth router — setup, login, and current user info."""
+
+from fastapi import APIRouter, Response
+
+router = APIRouter()
+
+
+@router.post("/setup", status_code=501)
+def setup():
+    """First-boot admin password setup."""
+    return Response(status_code=501, content="Not Implemented")
+
+
+@router.post("/login", status_code=501)
+def login():
+    """Login, returns JWT."""
+    return Response(status_code=501, content="Not Implemented")
+
+
+@router.get("/me", status_code=501)
+def me():
+    """Current user info."""
+    return Response(status_code=501, content="Not Implemented")
diff --git a/backend/routers/endpoints.py b/backend/routers/endpoints.py
new file mode 100644
index 0000000..36163b1
--- /dev/null
+++ b/backend/routers/endpoints.py
@@ -0,0 +1,37 @@
+"""Endpoints router — LLM target management."""
+
+import uuid
+
+from fastapi import APIRouter, Response
+
+router = APIRouter()
+
+
+@router.get("/", status_code=501)
+def list_endpoints():
+    """List configured LLM endpoints."""
+    return Response(status_code=501, content="Not Implemented")
+
+
+@router.post("/", status_code=501)
+def create_endpoint():
+    """Add endpoint (URL, API key, label)."""
+    return Response(status_code=501, content="Not Implemented")
+
+
+@router.put("/{endpoint_id}", status_code=501)
+def update_endpoint(endpoint_id: uuid.UUID):
+    """Update endpoint."""
+    return Response(status_code=501, content="Not Implemented")
+
+
+@router.delete("/{endpoint_id}", status_code=501)
+def delete_endpoint(endpoint_id: uuid.UUID):
+    """Remove endpoint."""
+    return Response(status_code=501, content="Not Implemented")
+
+
+@router.post("/{endpoint_id}/test", status_code=501)
+def test_endpoint(endpoint_id: uuid.UUID):
+    """Test connectivity and list available models."""
+    return Response(status_code=501, content="Not Implemented")
diff --git a/backend/routers/experiments.py b/backend/routers/experiments.py
new file mode 100644
index 0000000..9ecaca1
--- /dev/null
+++ b/backend/routers/experiments.py
@@ -0,0 +1,61 @@
+"""Experiments router — CRUD and sweep controls."""
+
+import uuid
+
+from fastapi import APIRouter, Response
+
+router = APIRouter()
+
+
+@router.get("/", status_code=501)
+def list_experiments():
+    """List experiments (filter by project)."""
+    return Response(status_code=501, content="Not Implemented")
+
+
+@router.post("/", status_code=501)
+def create_experiment():
+    """Create experiment."""
+    return Response(status_code=501, content="Not Implemented")
+
+
+@router.get("/{experiment_id}", status_code=501)
+def get_experiment(experiment_id: uuid.UUID):
+    """Experiment detail with run summaries."""
+    return Response(status_code=501, content="Not Implemented")
+
+
+@router.put("/{experiment_id}", status_code=501)
+def update_experiment(experiment_id: uuid.UUID):
+    """Update experiment config."""
+    return Response(status_code=501, content="Not Implemented")
+
+
+@router.delete("/{experiment_id}", status_code=501)
+def delete_experiment(experiment_id: uuid.UUID):
+    """Delete experiment."""
+    return Response(status_code=501, content="Not Implemented")
+
+
+@router.post("/{experiment_id}/sweep", status_code=501)
+def start_sweep(experiment_id: uuid.UUID):
+    """Start a sweep (grid, random, or guided)."""
+    return Response(status_code=501, content="Not Implemented")
+
+
+@router.post("/{experiment_id}/pause", status_code=501)
+def pause_sweep(experiment_id: uuid.UUID):
+    """Pause running sweep."""
+    return Response(status_code=501, content="Not Implemented")
+
+
+@router.post("/{experiment_id}/resume", status_code=501)
+def resume_sweep(experiment_id: uuid.UUID):
+    """Resume paused sweep."""
+    return Response(status_code=501, content="Not Implemented")
+
+
+@router.post("/{experiment_id}/stop", status_code=501)
+def stop_sweep(experiment_id: uuid.UUID):
+    """Stop sweep."""
+    return Response(status_code=501, content="Not Implemented")
diff --git a/backend/routers/export.py b/backend/routers/export.py
new file mode 100644
index 0000000..5cc04c2
--- /dev/null
+++ b/backend/routers/export.py
@@ -0,0 +1,31 @@
+"""Export router — export experiment results in various formats."""
+
+import uuid
+
+from fastapi import APIRouter, Response
+
+router = APIRouter()
+
+
+@router.get("/experiments/{experiment_id}/best", status_code=501)
+def export_best(experiment_id: uuid.UUID):
+    """Best config as JSON."""
+    return Response(status_code=501, content="Not Implemented")
+
+
+@router.get("/experiments/{experiment_id}/env", status_code=501)
+def export_env(experiment_id: uuid.UUID):
+    """Best config as .env snippet."""
+    return Response(status_code=501, content="Not Implemented")
+
+
+@router.get("/experiments/{experiment_id}/yaml", status_code=501)
+def export_yaml(experiment_id: uuid.UUID):
+    """Best config as YAML."""
+    return Response(status_code=501, content="Not Implemented")
+
+
+@router.get("/experiments/{experiment_id}/report", status_code=501)
+def export_report(experiment_id: uuid.UUID):
+    """Full experiment report (markdown)."""
+    return Response(status_code=501, content="Not Implemented")
diff --git a/backend/routers/projects.py b/backend/routers/projects.py
new file mode 100644
index 0000000..aabcb3d
--- /dev/null
+++ b/backend/routers/projects.py
@@ -0,0 +1,37 @@
+"""Projects router — CRUD for projects."""
+
+import uuid
+
+from fastapi import APIRouter, Response
+
+router = APIRouter()
+
+
+@router.get("/", status_code=501)
+def list_projects():
+    """List projects."""
+    return Response(status_code=501, content="Not Implemented")
+
+
+@router.post("/", status_code=501)
+def create_project():
+    """Create project."""
+    return Response(status_code=501, content="Not Implemented")
+
+
+@router.get("/{project_id}", status_code=501)
+def get_project(project_id: uuid.UUID):
+    """Project detail with experiment summaries."""
+    return Response(status_code=501, content="Not Implemented")
+
+
+@router.put("/{project_id}", status_code=501)
+def update_project(project_id: uuid.UUID):
+    """Update project."""
+    return Response(status_code=501, content="Not Implemented")
+
+
+@router.delete("/{project_id}", status_code=501)
+def delete_project(project_id: uuid.UUID):
+    """Delete project and all experiments."""
+    return Response(status_code=501, content="Not Implemented")
diff --git a/backend/routers/runs.py b/backend/routers/runs.py
new file mode 100644
index 0000000..46a0937
--- /dev/null
+++ b/backend/routers/runs.py
@@ -0,0 +1,37 @@
+"""Runs router — execute, detail, score, and leaderboard."""
+
+import uuid
+
+from fastapi import APIRouter, Response
+
+router = APIRouter()
+
+
+@router.get("/experiments/{experiment_id}/runs", status_code=501)
+def list_runs(experiment_id: uuid.UUID):
+    """List runs with scores (sortable, filterable)."""
+    return Response(status_code=501, content="Not Implemented")
+
+
+@router.get("/{run_id}", status_code=501)
+def get_run(run_id: uuid.UUID):
+    """Run detail with stage results."""
+    return Response(status_code=501, content="Not Implemented")
+
+
+@router.post("/", status_code=501)
+def create_run():
+    """Execute a single run (ad-hoc)."""
+    return Response(status_code=501, content="Not Implemented")
+
+
+@router.post("/{run_id}/score", status_code=501)
+def score_run(run_id: uuid.UUID):
+    """Add human rating to a run."""
+    return Response(status_code=501, content="Not Implemented")
+
+
+@router.get("/experiments/{experiment_id}/leaderboard", status_code=501)
+def leaderboard(experiment_id: uuid.UUID):
+    """Top runs ranked by weighted score."""
+    return Response(status_code=501, content="Not Implemented")
diff --git a/backend/routers/webhooks.py b/backend/routers/webhooks.py
new file mode 100644
index 0000000..17bc4b4
--- /dev/null
+++ b/backend/routers/webhooks.py
@@ -0,0 +1,25 @@
+"""Webhooks router — manage webhook configurations."""
+
+import uuid
+
+from fastapi import APIRouter, Response
+
+router = APIRouter()
+
+
+@router.get("/", status_code=501)
+def list_webhooks():
+    """List webhook configs."""
+    return Response(status_code=501, content="Not Implemented")
+
+
+@router.post("/", status_code=501)
+def create_webhook():
+    """Create webhook."""
+    return Response(status_code=501, content="Not Implemented")
+
+
+@router.delete("/{webhook_id}", status_code=501)
+def delete_webhook(webhook_id: uuid.UUID):
+    """Remove webhook."""
+    return Response(status_code=501, content="Not Implemented")
diff --git a/backend/tests/test_routers.py b/backend/tests/test_routers.py
new file mode 100644
index 0000000..9a1c9e5
--- /dev/null
+++ b/backend/tests/test_routers.py
@@ -0,0 +1,224 @@
+"""Tests for router stubs — verify all routes are mounted and return 501."""
+
+import pytest
+from fastapi.testclient import TestClient
+
+
+@pytest.fixture()
+def client(tmp_path, monkeypatch):
+    """Create a test client with a temporary database."""
+    monkeypatch.setenv("DATA_DIR", str(tmp_path))
+    monkeypatch.setenv("DATABASE_URL", "")
+    monkeypatch.setenv("REDIS_URL", "")
+
+    # Reload config to pick up test env
+    import importlib
+    import config as config_mod
+    importlib.reload(config_mod)
+
+    import main as main_mod
+    importlib.reload(main_mod)
+
+    with TestClient(main_mod.app) as c:
+        yield c
+
+
+# ---- Auth router (/api/auth) ----
+
+def test_auth_setup(client):
+    resp = client.post("/api/auth/setup")
+    assert resp.status_code == 501
+
+
+def test_auth_login(client):
+    resp = client.post("/api/auth/login")
+    assert resp.status_code == 501
+
+
+def test_auth_me(client):
+    resp = client.get("/api/auth/me")
+    assert resp.status_code == 501
+
+
+# ---- Projects router (/api/projects) ----
+
+def test_projects_list(client):
+    resp = client.get("/api/projects/")
+    assert resp.status_code == 501
+
+
+def test_projects_create(client):
+    resp = client.post("/api/projects/")
+    assert resp.status_code == 501
+
+
+def test_projects_get(client):
+    resp = client.get("/api/projects/00000000-0000-0000-0000-000000000001")
+    assert resp.status_code == 501
+
+
+def test_projects_update(client):
+    resp = client.put("/api/projects/00000000-0000-0000-0000-000000000001")
+    assert resp.status_code == 501
+
+
+def test_projects_delete(client):
+    resp = client.delete("/api/projects/00000000-0000-0000-0000-000000000001")
+    assert resp.status_code == 501
+
+
+# ---- Experiments router (/api/experiments) ----
+
+def test_experiments_list(client):
+    resp = client.get("/api/experiments/")
+    assert resp.status_code == 501
+
+
+def test_experiments_create(client):
+    resp = client.post("/api/experiments/")
+    assert resp.status_code == 501
+
+
+def test_experiments_get(client):
+    resp = client.get("/api/experiments/00000000-0000-0000-0000-000000000001")
+    assert resp.status_code == 501
+
+
+def test_experiments_update(client):
+    resp = client.put("/api/experiments/00000000-0000-0000-0000-000000000001")
+    assert resp.status_code == 501
+
+
+def test_experiments_delete(client):
+    resp = client.delete("/api/experiments/00000000-0000-0000-0000-000000000001")
+    assert resp.status_code == 501
+
+
+def test_experiments_sweep(client):
+    resp = client.post("/api/experiments/00000000-0000-0000-0000-000000000001/sweep")
+    assert resp.status_code == 501
+
+
+def test_experiments_pause(client):
+    resp = client.post("/api/experiments/00000000-0000-0000-0000-000000000001/pause")
+    assert resp.status_code == 501
+
+
+def test_experiments_resume(client):
+    resp = client.post("/api/experiments/00000000-0000-0000-0000-000000000001/resume")
+    assert resp.status_code == 501
+
+
+def test_experiments_stop(client):
+    resp = client.post("/api/experiments/00000000-0000-0000-0000-000000000001/stop")
+    assert resp.status_code == 501
+
+
+# ---- Runs router (/api/runs) ----
+
+def test_runs_list(client):
+    resp = client.get("/api/runs/experiments/00000000-0000-0000-0000-000000000001/runs")
+    assert resp.status_code == 501
+
+
+def test_runs_get(client):
+    resp = client.get("/api/runs/00000000-0000-0000-0000-000000000001")
+    assert resp.status_code == 501
+
+
+def test_runs_create(client):
+    resp = client.post("/api/runs/")
+    assert resp.status_code == 501
+
+
+def test_runs_score(client):
+    resp = client.post("/api/runs/00000000-0000-0000-0000-000000000001/score")
+    assert resp.status_code == 501
+
+
+def test_runs_leaderboard(client):
+    resp = client.get("/api/runs/experiments/00000000-0000-0000-0000-000000000001/leaderboard")
+    assert resp.status_code == 501
+
+
+# ---- Endpoints router (/api/endpoints) ----
+
+def test_endpoints_list(client):
+    resp = client.get("/api/endpoints/")
+    assert resp.status_code == 501
+
+
+def test_endpoints_create(client):
+    resp = client.post("/api/endpoints/")
+    assert resp.status_code == 501
+
+
+def test_endpoints_update(client):
+    resp = client.put("/api/endpoints/00000000-0000-0000-0000-000000000001")
+    assert resp.status_code == 501
+
+
+def test_endpoints_delete(client):
+    resp = client.delete("/api/endpoints/00000000-0000-0000-0000-000000000001")
+    assert resp.status_code == 501
+
+
+def test_endpoints_test(client):
+    resp = client.post("/api/endpoints/00000000-0000-0000-0000-000000000001/test")
+    assert resp.status_code == 501
+
+
+# ---- Export router (/api/export) ----
+
+def test_export_best(client):
+    resp = client.get("/api/export/experiments/00000000-0000-0000-0000-000000000001/best")
+    assert resp.status_code == 501
+
+
+def test_export_env(client):
+    resp = client.get("/api/export/experiments/00000000-0000-0000-0000-000000000001/env")
+    assert resp.status_code == 501
+
+
+def test_export_yaml(client):
+    resp = client.get("/api/export/experiments/00000000-0000-0000-0000-000000000001/yaml")
+    assert resp.status_code == 501
+
+
+def test_export_report(client):
+    resp = client.get("/api/export/experiments/00000000-0000-0000-0000-000000000001/report")
+    assert resp.status_code == 501
+
+
+# ---- Webhooks router (/api/webhooks) ----
+
+def test_webhooks_list(client):
+    resp = client.get("/api/webhooks/")
+    assert resp.status_code == 501
+
+
+def test_webhooks_create(client):
+    resp = client.post("/api/webhooks/")
+    assert resp.status_code == 501
+
+
+def test_webhooks_delete(client):
+    resp = client.delete("/api/webhooks/00000000-0000-0000-0000-000000000001")
+    assert resp.status_code == 501
+
+
+# ---- Admin router (/api/admin) ----
+
+def test_admin_get_settings(client):
+    resp = client.get("/api/admin/settings")
+    assert resp.status_code == 501
+
+
+def test_admin_update_settings(client):
+    resp = client.put("/api/admin/settings")
+    assert resp.status_code == 501
+
+
+def test_admin_stats(client):
+    resp = client.get("/api/admin/stats")
+    assert resp.status_code == 501