docs: consolidate tag documentation and improve cross-references

- Make request_tags.md the single source of truth for all tag options
- Add cross-reference from cost_tracking.md to request_tags.md
- Document both direct tags and metadata.tags formats
- Add key/team tag setup and custom header tracking to request_tags.md
- Reduce duplication and make navigation clearer

Co-authored-by: Ishaan Jaff <ishaan-jaff@users.noreply.github.com>

docs/my-website/docs/proxy/cost_tracking.md

@@ -326,6 +326,10 @@ See our [Swagger API](https://litellm-api.up.railway.app/#/Budget%20%26%20Spend%
 
 ## Custom Tags
 
+:::tip See Full Request Tags Documentation
+For comprehensive documentation on all tag options including `x-litellm-tags` header, request body `tags`, and config-based tags, see the dedicated [Request Tags](./request_tags.md) page.
+:::
+
 Requirements:
 
 - Virtual Keys & a database should be set up, see [virtual keys](https://docs.litellm.ai/docs/proxy/virtual_keys)

docs/my-website/docs/proxy/request_tags.md

@@ -1,9 +1,16 @@
+import Tabs from '@theme/Tabs';
+import TabItem from '@theme/TabItem';
+
 # Request Tags for Spend Tracking
 
 Add tags to model deployments to track spend by environment, AWS account, or any custom label.
 
 Tags appear in the `request_tags` field of LiteLLM spend logs.
 
+:::info Requirements
+Virtual Keys & a database should be set up. See [Virtual Keys Setup](./virtual_keys.md).
+:::
+
 ## Config Setup
 
 Set tags on model deployments in `config.yaml`:
@@ -62,7 +69,10 @@ The header accepts:
 
 ### Option 3: Use Request Body `tags`
 
-Pass tags directly in the request body:
+Pass tags directly in the request body. Both formats are supported:
+
+<Tabs>
+<TabItem value="direct" label="Direct tags Field">
 
 ```bash
 curl -X POST 'http://0.0.0.0:4000/chat/completions' \
@@ -75,12 +85,85 @@ curl -X POST 'http://0.0.0.0:4000/chat/completions' \
   }'
 ```
 
+</TabItem>
+
+<TabItem value="metadata" label="Metadata Nested">
+
+```bash
+curl -X POST 'http://0.0.0.0:4000/chat/completions' \
+  -H 'Authorization: Bearer sk-1234' \
+  -H 'Content-Type: application/json' \
+  -d '{
+    "model": "gpt-4",
+    "messages": [{"role": "user", "content": "Hello"}],
+    "metadata": {
+      "tags": ["team-stripe", "production", "us-east-1"]
+    }
+  }'
+```
+
+</TabItem>
+</Tabs>
+
 The `tags` field must be an array of strings.
 
 :::info
 When tags are provided via header or request body, they override any tags configured in the model deployment.
 :::
 
+## Set Tags on Keys or Teams
+
+You can also set default tags at the API key or team level:
+
+<Tabs>
+<TabItem value="key" label="Set on Key">
+
+```bash
+curl -L -X POST 'http://0.0.0.0:4000/key/generate' \
+  -H 'Authorization: Bearer sk-1234' \
+  -H 'Content-Type: application/json' \
+  -d '{
+    "metadata": {
+      "tags": ["customer-stripe", "tier-premium"]
+    }
+  }'
+```
+
+</TabItem>
+<TabItem value="team" label="Set on Team">
+
+```bash
+curl -L -X POST 'http://0.0.0.0:4000/team/new' \
+  -H 'Authorization: Bearer sk-1234' \
+  -H 'Content-Type: application/json' \
+  -d '{
+    "metadata": {
+      "tags": ["team-engineering", "department-ai"]
+    }
+  }'
+```
+
+</TabItem>
+</Tabs>
+
+## Advanced: Custom Header Tracking
+
+Track spend using any custom header by adding it to your config:
+
+```yaml
+litellm_settings:
+  extra_spend_tag_headers:
+    - "x-custom-header"
+    - "x-customer-id"
+```
+
+**Disable User-Agent tracking:**
+
+```yaml
+litellm_settings:
+  disable_add_user_agent_to_request_tags: true
+```
+
 ## Spend Logs
 
 The tag from the model config appears in `LiteLLM_SpendLogs`:
@@ -96,5 +179,6 @@ The tag from the model config appears in `LiteLLM_SpendLogs`:
 
 ## Related
 
-- [Spend Tracking Overview](cost_tracking.md)
+- [Spend Tracking Overview](cost_tracking.md) - Complete tutorial on tracking spend with tags
 - [Tag Budgets](tag_budgets.md) - Set budget limits per tag
+- [Virtual Keys Setup](virtual_keys.md) - Required for tag tracking