Sideline Number Checker API — official examples | CheckNumber

This repository documents the CheckNumber Sideline Number Checker API integration contract using facts from the expansion manifest.

• Product page: https://checknumber.ai/products/sideline
• API base URL: https://api.checknumber.ai
• Authentication: X-API-Key
• API key environment variable: CHECKNUMBER_API_KEY
• License: MIT

Processing model

This is a file-based asynchronous API. Submit an authorized text file, poll the task until exported, then download the result URL. It is not a realtime single-identifier endpoint.

curl -X POST "https://api.checknumber.ai/v1/tasks" -H "X-API-Key: ${CHECKNUMBER_API_KEY}" -F "file=@examples/numbers.txt" -F "task_type=sideline"
curl -X POST "https://api.checknumber.ai/v1/gettasks" -H "X-API-Key: ${CHECKNUMBER_API_KEY}" -F "task_id=YOUR_TASK_ID"

Products and limits

Code	Name	Input	Limits	Result fields	Documentation
sideline	Number Checker	phone	500–10000000 rows	Number, activated	docs

Response and boundaries

• Treat only an explicit determined result as a positive or negative classification; undetermined/exists=false is not a negative.
• Authentication keys must come from environment variables or a secret manager; never commit keys or call private/internal endpoints.
• Product prices can change. Check the official pricing page at runtime; this repository intentionally does not hard-code a price.
• Use only identifiers you are authorized to process and follow applicable privacy, platform, and data-protection requirements.

Runnable examples

Seven self-contained examples are provided under examples/: Python, Node.js, Go, Java, C#, PHP, and Shell each implement the full submit → poll → download workflow with HTTP error handling. Set the server-side API-key environment variable before running them.

Official resources

• sideline: https://docs.checknumber.ai/sideline-checker
• Pricing: https://checknumber.ai/pricing
• OpenAPI contract: openapi.yaml

Last reviewed: 2026-08-18.