> ## Documentation Index > Fetch the complete documentation index at: https://technologychecker.io/docs/llms.txt > Use this file to discover all available pages before exploring further. # Preview lead list count API > Estimate how many domains a filter set matches and what building it would cost, before you commit. Free. ## Frequently asked questions It is a fast approximation designed to drive a live counter as someone adjusts filters, not an exact count. Billing always happens on the actual delivered row count, never on this number, so an overestimate never costs you anything. Technology, keyword, country, industry and employee filters all move it. Among the website filters, `has_email` and `has_phone` apply coverage factors, while `languages` and `web_countries` are informational and do not move the estimate — they still filter the real build. Yes, for 5 minutes per unique filter set, so a user toggling back and forth does not re-run the estimate each time. One credit per row we would deliver. Cap it by setting `list_size` when you [create the list](/docs/api-reference/lead-lists/create-lead-list-api) — that is the maximum you can be charged. ## OpenAPI ````yaml POST /v1/leads/preview-count openapi: 3.1.0 info: title: TechnologyChecker API description: >- Discover technology stacks, track market trends, and enrich data with company intelligence. version: 1.0.0 contact: name: TechnologyChecker Support email: support@technologychecker.io url: https://technologychecker.io servers: - url: https://api.technologychecker.io description: Production security: - bearerAuth: [] tags: - name: Domain technologies description: Look up technologies detected on any domain - name: Technology data description: Search, look up, and get details on tracked technologies - name: Market intelligence description: Technology stats, trends, and market share - name: Company data description: Firmographic and company intelligence - name: Live detection description: Real-time technology detection with browser rendering - name: Signals description: >- Intent signals derived from technology state transitions: who adopted, who churned, who switched, and who has a gap in their stack. - name: Alerts description: >- Saved signal queries delivered to your webhook. Every signal you can query, you can subscribe to. - name: Audiences description: >- Saved groups of domains — uploaded lists or computed recipes — that you can profile, slice and monitor. - name: Lead lists description: >- Build and export targeted domain lists combining technology detection with company data. paths: /v1/leads/preview-count: post: tags: - Lead lists summary: Preview lead list count API description: >- Estimate how many domains a filter set will match, and what building it would cost, before you commit. Free — use it as the live counter on a filter builder. The estimate is a fast approximation and results are cached for 5 minutes per filter set. Billing always happens on the actual row count, never on this number. operationId: previewLeadListCount requestBody: required: true content: application/json: schema: $ref: '#/components/schemas/LeadListFilters' example: technologies: ids: - 2 - 7 logic: or keywords: include: - shop exclude: - health website_type: company_only countries: - United States - Germany industries: - Software Development employees: - 51-200 - 201-500 responses: '200': description: Estimated match count and credit cost content: application/json: schema: type: object properties: success: type: boolean example: true data: type: object properties: estimated_count: type: integer example: 518300 credit_cost: type: integer description: One credit per row delivered. example: 518300 filters_applied: type: object additionalProperties: type: integer example: technologies: 2 countries: 2 industries: 1 employees: 2 '400': $ref: '#/components/responses/BadRequest' '401': $ref: '#/components/responses/Unauthorized' '429': $ref: '#/components/responses/RateLimited' components: schemas: LeadListFilters: type: object description: >- The filter set that defines a lead list. Technology filters and company filters combine with AND. properties: technologies: type: object properties: ids: type: array items: type: integer example: - 2 - 7 logic: type: string enum: - or - and - and_not default: or description: >- `or` matches domains running any listed technology. `and` requires all of them. `and_not` requires the first and excludes the rest. keywords: type: object properties: include: type: array items: type: string example: - shop exclude: type: array items: type: string example: - health website_type: type: string example: company_only countries: type: array items: type: string example: - United States - Germany industries: type: array items: type: string example: - Software Development employees: type: array items: type: string example: - 51-200 - 201-500 has_email: type: boolean description: Only domains where the crawler found an email address. has_phone: type: boolean description: Only domains where the crawler found a phone number. languages: type: array items: type: string example: - en web_countries: type: array items: type: string description: >- ISO-2 codes or English names. Unresolvable values are rejected at create time. example: - USA ApiError: type: object properties: success: type: boolean example: false error: type: object properties: code: type: string example: UNAUTHORIZED message: type: string example: Missing or invalid API key responses: BadRequest: description: Invalid or missing parameters content: application/json: schema: $ref: '#/components/schemas/ApiError' example: success: false error: code: VALIDATION_ERROR message: >- Provide exactly one scope: technology_id, technology or category_id. Unauthorized: description: Missing or invalid API key content: application/json: schema: $ref: '#/components/schemas/ApiError' RateLimited: description: Rate limit exceeded content: application/json: schema: $ref: '#/components/schemas/ApiError' securitySchemes: bearerAuth: type: http scheme: bearer description: >- API key in format `tapi_live_[32-char]` (live) or `tapi_test_[32-char]` (test) ````