feat(azure-cost): add App Service optimization guide

- Add services/appservice/azure-app-service.md with plan rightsizing,
  idle slot detection, dev/test pricing, and Resource Graph queries
- Consolidate service routing in workflow.md into compact table format
- Add 2 vally eval stimuli for App Service cost routing
- Trim storage intro and SKILL.md to stay within token budgets

Partial progress on #2524

Author: jongio

evals/azure-cost/eval.yaml

@@ -371,6 +371,48 @@ stimuli:
         config:
           pattern: "(?i)fatal error|unhandled exception|stack trace"
 
+  # ═══════════════════════════════════════════
+  # App Service Cost Optimization routing prompts
+  # ═══════════════════════════════════════════
+
+  # ── appservice-idle-slots-prompt ──
+  # Assertions: softCheckSkill + isSkillInvoked (invocation rate ≥ 80%)
+  - name: "App Service idle deployment slots cost"
+    prompt: "I have deployment slots on my App Service that aren't being used, how much are they costing me?"
+    tags:
+      type: integration
+      tier: full
+      cost: llm
+      area: routing
+      earlyTerminate: '[{"type":"skill-call","skill":"azure-cost"},{"type":"tool-call-count","count":3}]'
+    graders:
+      - type: skill-invocation
+        config:
+          required:
+            - azure-cost
+      - type: output-not-matches
+        config:
+          pattern: "(?i)fatal error|unhandled exception|stack trace"
+
+  # ── appservice-plan-downgrade-prompt ──
+  # Assertions: softCheckSkill + isSkillInvoked (invocation rate ≥ 80%)
+  - name: "App Service plan downgrade savings"
+    prompt: "Can I save money by downgrading my Premium App Service plans in dev/test to a cheaper tier?"
+    tags:
+      type: integration
+      tier: full
+      cost: llm
+      area: routing
+      earlyTerminate: '[{"type":"skill-call","skill":"azure-cost"},{"type":"tool-call-count","count":3}]'
+    graders:
+      - type: skill-invocation
+        config:
+          required:
+            - azure-cost
+      - type: output-not-matches
+        config:
+          pattern: "(?i)fatal error|unhandled exception|stack trace"
+
   # ═══════════════════════════════════════════
   # Response quality tests
   # ═══════════════════════════════════════════

plugin/skills/azure-cost/SKILL.md

@@ -32,14 +32,11 @@ Query historical costs, forecast future spending, optimize to reduce waste.
 - Subscription: `/subscriptions/<id>`
 - Resource Group: `/subscriptions/<id>/resourceGroups/<name>`
 - Management Group: `/providers/Microsoft.Management/managementGroups/<id>`
-- Billing Account: `/providers/Microsoft.Billing/billingAccounts/<id>`
 
-## Service-Specific Optimization
+## Service Optimization Guides
 
-- [Redis](cost-optimization/services/redis/azure-cache-for-redis.md)
-- [Storage](cost-optimization/services/storage/azure-storage.md)
+[Redis](cost-optimization/services/redis/azure-cache-for-redis.md) | [Storage](cost-optimization/services/storage/azure-storage.md) | [App Service](cost-optimization/services/appservice/azure-app-service.md)
 
 ## References
 
 - [MCP Tools, Best Practices, Safety](references/tools-and-best-practices.md)
-- [SDK: Redis .NET](cost-optimization/sdk/azure-resource-manager-redis-dotnet.md)

plugin/skills/azure-cost/cost-optimization/services/appservice/azure-app-service.md

@@ -0,0 +1,83 @@
+## Azure App Service Cost Optimization
+
+Reference guide for reducing App Service costs through plan rightsizing, idle slot cleanup, and dev/test pricing.
+
+## Cost Optimization Rules
+
+| Priority | Rule | Detection Logic | Recommendation | Avg Savings |
+|----------|------|----------------|----------------|-------------|
+| 🔴 Critical | Stopped App on Paid Plan | `state == 'Stopped'` AND `sku.tier != 'Free/Shared'` | Delete or move to Free tier (stopped apps still incur plan cost) | $50-500/mo |
+| 🔴 Critical | Empty App Service Plan | Plan has zero apps deployed | Delete the plan | $50-400/mo |
+| 🟠 High | Premium in Non-Production | `sku.tier in ['PremiumV2','PremiumV3']` AND `tags.environment in ['dev','test','staging']` | Downgrade to Basic or Standard | $100-600/mo |
+| 🟠 High | Idle Deployment Slots | Non-production slots with zero traffic for 14+ days | Delete unused slots (each slot = separate app instance cost) | $50-300/mo |
+| 🟠 High | Over-Provisioned Plan | CPU avg <20% AND memory avg <30% over 14 days | Scale down SKU or reduce instance count | $50-400/mo |
+| 🟡 Medium | No Auto-Scale Rules | Production plan with fixed instance count >2 | Add auto-scale rules to scale in during low traffic | $30-200/mo |
+| 🟡 Medium | Missing Dev/Test Pricing | Dev/test workloads on regular pricing | Enable Dev/Test pricing via subscription offer | 30-55% savings |
+| 🟡 Medium | Always On for Non-Production | `alwaysOn == true` on dev/test apps | Disable Always On (apps cold-start on first request) | Reduced idle cost |
+| 🟢 Low | Untagged App Service | Missing `environment`, `owner`, or `costCenter` tags | Apply tags for cost allocation | N/A |
+| 🟢 Low | Old Deployment Slots | Slots older than 90 days not used for blue-green | Review if still needed | Variable |
+
+## Plan Tier Decision Matrix
+
+| Workload | Recommended Tier | Key Features |
+|----------|-----------------|--------------|
+| Dev/test, prototypes | Free / Basic B1 | No SLA, limited scale |
+| Low-traffic production | Standard S1 | Auto-scale, slots, backups |
+| High-traffic production | Premium P1v3 | Better perf, more slots, VNET |
+| Isolated compliance | Isolated I1v2 | Private environment, max scale |
+
+## Resource Graph Queries
+
+**Find stopped apps on paid plans:**
+
+```kql
+Resources
+| where type =~ 'microsoft.web/sites'
+| where properties.state =~ 'Stopped'
+| where isnotempty(properties.serverFarmId)
+| project name, resourceGroup, kind, state=properties.state
+```
+
+**Find empty App Service Plans:**
+
+```kql
+Resources
+| where type =~ 'microsoft.web/serverfarms'
+| where properties.numberOfSites == 0
+| project name, resourceGroup, sku=sku.name, location
+```
+
+**Find Premium plans in non-production:**
+
+```kql
+Resources
+| where type =~ 'microsoft.web/serverfarms'
+| where sku.tier in~ ('PremiumV2', 'PremiumV3', 'Premium')
+| where tags.environment in~ ('dev', 'test', 'staging', 'sandbox')
+| project name, resourceGroup, sku=sku.name, tier=sku.tier, tags
+```
+
+## Tools & Commands
+
+**MCP Tool:** `azure__appservice` for listing and managing App Service resources
+
+**Azure CLI:**
+- `az appservice plan list --resource-group <rg>` - List plans
+- `az appservice plan show --name <plan> --resource-group <rg>` - Plan details
+- `az webapp list --resource-group <rg>` - List web apps
+- `az webapp show --name <app> --resource-group <rg>` - App details
+- `az webapp deployment slot list --name <app> --resource-group <rg>` - List slots
+- `az monitor metrics list --resource <plan-id> --metric CpuPercentage --interval PT1H` - CPU utilization
+- `az monitor metrics list --resource <plan-id> --metric MemoryPercentage --interval PT1H` - Memory utilization
+
+## Pricing Quick Reference
+
+Approximate monthly costs (Linux, East US):
+- **Free F1**: $0 (60 min CPU/day, 1 GB RAM)
+- **Basic B1**: ~$13/mo (1 core, 1.75 GB)
+- **Standard S1**: ~$69/mo (1 core, 1.75 GB, auto-scale, slots)
+- **Premium P1v3**: ~$138/mo (2 cores, 8 GB, better perf)
+
+Each deployment slot runs as a separate instance at full plan cost. Windows plans cost ~30% more than Linux.
+
+Always validate from [official pricing](https://azure.microsoft.com/pricing/details/app-service/).

plugin/skills/azure-cost/cost-optimization/services/storage/azure-storage.md

@@ -1,6 +1,6 @@
 ## Azure Storage Cost Optimization
 
-Reference guide for identifying cost savings opportunities in Azure Storage accounts through tier analysis, lifecycle policies, and orphaned resource detection.
+Identify cost savings in Azure Storage through tier analysis, lifecycle policies, and orphaned resource detection.
 
 ## Subscription Input Options
 

plugin/skills/azure-cost/cost-optimization/workflow.md

@@ -57,13 +57,14 @@ azure__get_azure_bestpractices({
 
 Wait for user response before proceeding.
 
-## Step 1.7: Storage-Specific Analysis (Conditional)
+## Steps 1.7–1.75: Service-Specific Analysis (Conditional)
 
-**If the user requests Storage cost optimization**, load: [Azure Storage Cost Optimization](./services/storage/azure-storage.md)
+For service-focused requests, load the relevant guide and follow it. For general optimization, skip to Step 2.
 
-**Triggers:** "storage account cost", "blob storage savings", "LRS/GRS/ZRS downgrade", "storage lifecycle savings", "reduce storage spending".
-
-For Storage-only requests, follow the Storage reference. For general optimization that includes storage, continue to Step 2.
+| Triggers | Reference |
+|----------|-----------|
+| "storage account cost", "blob savings", "LRS/GRS downgrade", "storage lifecycle savings" | [Storage](./services/storage/azure-storage.md) |
+| "app service cost", "plan savings", "web app spending", "idle slots", "overprovisioned plan" | [App Service](./services/appservice/azure-app-service.md) |
 
 ## Step 1.8: AKS-Specific Analysis (Conditional)
 
@@ -75,14 +76,14 @@ For Storage-only requests, follow the Storage reference. For general optimizatio
 - User reports a cost spike, unusual cluster utilization, or wants budget alerts
 
 **Tool Selection:**
-- **Prefer MCP first**: Use `azure__aks` for AKS operations (list clusters, get node pools, inspect configuration) — it provides richer metadata and is consistent with AKS skill conventions in this repo
-- **Fall back to CLI**: Use `az aks` and `kubectl` only when the specific operation cannot be performed via the MCP surface
+- **Prefer MCP first**: Use `azure__aks` for AKS operations (list clusters, get node pools, inspect configuration)
+- **Fall back to CLI**: Use `az aks` and `kubectl` only when MCP doesn't cover the operation
 
-**Reference files (load only what is needed for the request):**
-- [Cost Analysis Add-on](./azure-aks-cost-addon.md) — enable namespace-level cost visibility
-- [Anomaly Investigation](./azure-aks-anomalies.md) — cost spikes, scaling events, budget alerts
+**Reference files:**
+- [Cost Analysis Add-on](./azure-aks-cost-addon.md)
+- [Anomaly Investigation](./azure-aks-anomalies.md)
 
-> **Note**: For general subscription-wide cost optimization (including AKS resource groups), continue with Step 2. For AKS-focused analysis, follow the instructions in the relevant reference file above.
+For general optimization (including AKS resource groups), continue to Step 2.
 
 ## Step 1.9: Choose Analysis Scope (for AKS-specific analysis)