> ## Documentation Index > Fetch the complete documentation index at: https://lava.so/docs/llms.txt > Use this file to discover all available pages before exploring further. # Synthesized answer with citations from the 9-provider fan-out > Same fan-out as /search/sources, plus an LLM synthesis pass that produces a cited answer. Returns `{ answer, citations, cost }` — the underlying sources are not echoed back; call /search/sources separately if you need the raw evidence pile. When the synthesis model fails (timeout, malformed structured output), the endpoint still returns 200 with `answer: null` and `cost.synthesis_error` set, but no result list. Charges sum of upstream provider costs + LLM token cost + $0.03 lava-search markup. ## OpenAPI ````yaml /openapi.json post /search/answer openapi: 3.0.0 info: title: Lava API description: >- Lava API enables businesses to implement usage-based billing for AI services. This API allows tracking, managing, and billing for third-party AI API usage through a forwarding system. version: 1.0.0 contact: name: Lava support url: https://www.lava.so/contact servers: - url: https://api.lava.so/v1/ description: Lava API v1 security: [] tags: - name: Authentication - name: Core Endpoints - name: Models - name: Services - name: Requests - name: Wallet - name: Payment Methods - name: Spend Keys - name: Usage - name: Checkout Sessions - name: Customers - name: Plans - name: Subscriptions - name: Meters - name: Webhooks - name: Secret Keys - name: Credit Bundles - name: Gateway Settings - name: Skills - name: News Data - name: Search - name: Enrich paths: /search/answer: post: tags: - Search summary: Synthesized answer with citations from the 9-provider fan-out description: >- Same fan-out as /search/sources, plus an LLM synthesis pass that produces a cited answer. Returns `{ answer, citations, cost }` — the underlying sources are not echoed back; call /search/sources separately if you need the raw evidence pile. When the synthesis model fails (timeout, malformed structured output), the endpoint still returns 200 with `answer: null` and `cost.synthesis_error` set, but no result list. Charges sum of upstream provider costs + LLM token cost + $0.03 lava-search markup. requestBody: required: true content: application/json: schema: type: object required: - q properties: q: type: string description: The query to answer providers: type: array items: type: string nullable: true description: >- Optional subset of providers (defaults to all 9). See /search/sources for valid ids. max_results_per_source: type: integer minimum: 1 maximum: 50 nullable: true since: type: string format: date-time nullable: true examples: cryptoQuery: value: q: >- Current state of NIST post-quantum standardization 2025-2026 — ML-KEM and ML-DSA deployment, FrodoKEM as a hedge, security margin against Module-LWE attacks responses: '200': description: >- Synthesized answer with citations. When the LLM step fails, `answer` is null and `cost.synthesis_error` is set; the rest of the payload is unchanged. Underlying sources are not echoed back — call /search/sources separately if needed. content: application/json: schema: type: object required: - answer - citations - cost properties: answer: type: string nullable: true description: >- Markdown answer citing sources via [N]. Null when the synthesis model failed. citations: type: array items: type: object required: - source - url - title properties: source: type: string url: type: string title: type: string cost: type: object required: - breakdown - llm_cost - markup - total properties: breakdown: type: object additionalProperties: type: string llm_cost: type: string description: >- Synthesis-model token cost as a decimal string. "0" when the synthesis call failed. markup: type: string total: type: string synthesis_error: type: string nullable: true description: >- Present when `answer` is null. Identifies the synthesis failure mode (e.g. "xai_500", "invalid_shape"). '400': description: Unknown provider id content: application/json: schema: $ref: '#/components/schemas/Error' '401': description: Unauthorized content: application/json: schema: $ref: '#/components/schemas/Error' '502': description: >- Every requested provider failed. No synthesis attempted, no markup charged. content: application/json: schema: $ref: '#/components/schemas/Error' security: - Auth: [] components: schemas: Error: type: object properties: error: type: object properties: message: type: string description: Human-readable error message describing what went wrong example: Invalid authentication credentials code: type: string description: Machine-readable error code describing what went wrong example: forward_token_json_invalid status: type: integer description: HTTP status code of the error example: 400 issues: type: array items: type: object properties: path: type: array items: type: string description: Path to the field that caused the validation error message: type: string description: Error message describing the validation issue required: - path - message description: >- Optional array of specific validation issues with their paths and messages example: - path: - model message: 'Missing required field: model' - path: - messages - '0' - content message: Invalid message content format required: - message - code - status required: - error securitySchemes: Auth: type: http scheme: bearer description: >- Bearer token authentication used for standard API calls. Format: 'Bearer YOUR_API_KEY' ````