Add /usage endpoint with token tracking, live balances, and cost calculations

README.md

@@ -59,7 +59,7 @@ cd ein-ai-proxy
 cp config.example.json config.json
 ```
 
-Edit `config.json` with your API keys:
+Edit `config.json` with your API keys and pricing:
 
 ```json
 {
@@ -69,10 +69,26 @@ Edit `config.json` with your API keys:
     "anthropic": { "apiKey": "sk-ant-..." },
     "zai":       { "apiKey": "your-zai-key" },
     "deepseek":  { "apiKey": "your-deepseek-key" }
+  },
+  "pricing": {
+    "anthropic": {
+      "inputPerMTok": 15,
+      "outputPerMTok": 75
+    },
+    "deepseek": {
+      "inputPerMTok": 0.27,
+      "outputPerMTok": 1.10
+    },
+    "zai": {
+      "type": "flat",
+      "monthlyCostUsd": 10
+    }
   }
 }
 ```
 
+**Pricing notes**: Rates are per million tokens (input/output). Update these values based on current provider pricing. Z.ai uses a flat-rate model ($10/mo) regardless of token usage.
+
 ### Run
 
 ```bash
@@ -185,6 +201,61 @@ curl https://ai.ein-softworks.com/health
 
 Returns the proxy status and current routing table. No authentication required.
 
+### Usage Statistics
+
+```bash
+curl https://ai.ein-softworks.com/usage
+```
+
+Returns comprehensive usage data grouped by provider:
+
+- **Per-model breakdown**: Requested model name, actual provider model, total + monthly token counts and request counts
+- **Cost calculations**: Dollar amounts for each model (based on pricing in `config.json`)
+- **Live balances**: Account balances from providers that support it (DeepSeek)
+- **Totals**: Aggregated request counts and costs across all models
+
+Example response:
+
+```json
+{
+  "service": "ein-ai-proxy",
+  "generatedAt": "2026-03-27T00:38:00.000Z",
+  "currentPeriod": "2026-03",
+  "providers": {
+    "anthropic": {
+      "balance": null,
+      "pricingNote": "No balance API available — check console.anthropic.com",
+      "models": {
+        "claude-opus-4-6": {
+          "routesTo": "claude-opus-4-6",
+          "total": { "inputTokens": 150000, "outputTokens": 50000, "requests": 42, "costUsd": 6.00 },
+          "monthly": { "inputTokens": 30000, "outputTokens": 10000, "requests": 8, "costUsd": 1.20 }
+        }
+      }
+    },
+    "deepseek": {
+      "balance": { "totalBalance": "8.52", "currency": "USD" },
+      "models": { ... }
+    },
+    "zai": {
+      "balance": null,
+      "pricing": "flat_rate",
+      "monthlyCostUsd": 10,
+      "models": { ... }
+    }
+  },
+  "totals": {
+    "totalRequests": 252,
+    "monthlyRequests": 53,
+    "totalCostUsd": 6.14,
+    "monthlyCostUsd": 1.24,
+    "note": "Cost excludes flat-rate models. Z.ai costs $10/mo regardless of usage."
+  }
+}
+```
+
+**Note**: Monthly totals reset on the 1st of each month. Usage data is persisted to `usage-data.json` in the proxy directory.
+
 ### Messages Endpoint
 
 ```bash