> ## Documentation Index > Fetch the complete documentation index at: https://docs.costgraph.ai/llms.txt > Use this file to discover all available pages before exploring further. # Create a virtual tag rule > Adds a rule at the bottom of its tag key so it cannot outrank an existing rule. The predicate, and the value expression of an inherited rule, are compiled before the rule is stored. A rule is written one of three ways and exactly one may be sent: expression as CostQL text, clause as a single chip, or node as a tree of chips. A node is rendered server-side by the same renderer the decompose endpoint round-trips through, so a rule saved from chips reads back as the identical tree, and sending node together with expression or clause is a 400 rather than a silent pick. Every leaf of a node is checked like a flat clause, so a tree cannot smuggle in a field or operator the clause path would refuse. ## OpenAPI ````yaml /api-reference/costgraph/openapi.json post /api/v1/tenant/virtual-tags openapi: 3.0.0 info: description: Read and manage your CostGraph organization, spend, alerts, and settings. title: CostGraph API contact: {} version: '1.0' servers: - url: https://api.costgraph.ai security: [] tags: - name: ai x-group: AI - name: ai-serving x-group: AI serving - name: anomalies x-group: Anomalies - name: auth x-group: Auth - name: billing x-group: Billing - name: billing-export x-group: Billing export - name: budgets x-group: Budgets - name: ci x-group: CI - name: compute-recommendations x-group: Compute recommendations - name: config x-group: Config - name: cost x-group: Cost - name: gpus x-group: GPUs - name: graphai x-group: Graph AI - name: infracost x-group: Infracost - name: integrations x-group: Integrations - name: invitations x-group: Invitations - name: kubernetes-clusters x-group: Kubernetes clusters - name: marketplace x-group: Marketplace - name: network-requests x-group: Network requests - name: notifications x-group: Notifications - name: oauth x-group: OAuth - name: oauth-clients x-group: OAuth clients - name: opencost x-group: OpenCost - name: organization x-group: Audit log - name: organizations x-group: Organizations - name: placement-alternatives x-group: Placement alternatives - name: reports x-group: Reports - name: service-map x-group: Service map - name: settings x-group: Settings - name: sso x-group: Single sign-on - name: tenants x-group: Tenants - name: user x-group: Users - name: virtual-machines x-group: Virtual machines - name: virtual-tags x-group: Virtual tags - name: workflows x-group: Workflows paths: /api/v1/tenant/virtual-tags: post: tags: - virtual-tags summary: Create a virtual tag rule description: >- Adds a rule at the bottom of its tag key so it cannot outrank an existing rule. The predicate, and the value expression of an inherited rule, are compiled before the rule is stored. A rule is written one of three ways and exactly one may be sent: expression as CostQL text, clause as a single chip, or node as a tree of chips. A node is rendered server-side by the same renderer the decompose endpoint round-trips through, so a rule saved from chips reads back as the identical tree, and sending node together with expression or clause is a 400 rather than a silent pick. Every leaf of a node is checked like a flat clause, so a tree cannot smuggle in a field or operator the clause path would refuse. requestBody: content: application/json: schema: $ref: '#/components/schemas/virtualtag.RuleRequest' description: Rule to create required: true responses: '201': description: Created content: application/json: schema: allOf: - $ref: '#/components/schemas/responses.SuccessResponse' - type: object properties: data: $ref: '#/components/schemas/virtualtag.Rule' '400': description: Bad Request content: application/json: schema: $ref: '#/components/schemas/responses.ErrorResponse' '500': description: Internal Server Error content: application/json: schema: $ref: '#/components/schemas/responses.ErrorResponse' security: - BearerAuth: [] components: schemas: virtualtag.RuleRequest: type: object properties: clause: $ref: '#/components/schemas/virtualtag.Clause' description: type: string expression: type: string inherited_from: type: string key: type: string node: $ref: '#/components/schemas/virtualtag.Node' origin: type: string rule_type: type: string scope: type: string source_text: type: string valid_from: type: string valid_to: type: string value: type: string responses.SuccessResponse: type: object required: - message - status properties: data: {} message: type: string example: some message status: type: string example: success virtualtag.Rule: type: object properties: active: type: boolean created_at: type: string description: type: string expression: type: string expression_hash: type: string field: type: string id: type: string inherited_from: type: string key: type: string match_value: type: string operator: type: string origin: type: string rank: type: number rule_type: type: string scope: type: string source_text: type: string tenant_id: type: string updated_at: type: string valid_from: type: string valid_to: type: string value: type: string responses.ErrorResponse: type: object required: - message - status properties: message: type: string example: some message status: type: string example: error virtualtag.Clause: type: object properties: field: type: string match_value: type: string operator: type: string virtualtag.Node: type: object properties: children: type: array items: $ref: '#/components/schemas/virtualtag.Node' clause: $ref: '#/components/schemas/virtualtag.Clause' kind: type: string securitySchemes: BearerAuth: description: Enter "Bearer {token}" type: apiKey name: Authorization in: header ```` This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.