API Pagination Calculator — Offset & Cursor Tool

How to Use the API Pagination Calculator:

1. Enter Total Items: Input the total number of records in your collection or dataset. This is the full count before any pagination is applied — for example, the total number of rows returned by a SELECT COUNT(*) query. The calculator uses this to determine the total number of pages and whether a next or previous page exists.

2. Set Page Size: Enter how many items should appear per page (also called limit or per_page in many APIs). Common values are 10, 20, 25, 50, or 100. Smaller page sizes reduce payload but require more requests; larger pages reduce round-trips but increase response size.

3. Enter Current Page: Provide the 1-indexed page number you want to calculate parameters for. For example, entering page 3 with 10 items per page will produce an offset of 20. If the page exceeds the total pages, it will be automatically clamped to the last valid page.

4. Provide a Base URL (optional): Enter your API endpoint URL (e.g., https://api.example.com/users). This is used to generate the Link header and example request URLs. You can use a placeholder if your URL is not yet determined — any URL works as a template.

5. Load a Preset: Use the preset buttons at the top to quickly populate common scenarios: small datasets (50 items), medium datasets (500 items), large datasets (10,000 items), or a typical REST API setup (1,000 items, 20/page, page 2). Presets are useful for learning the tool or verifying your own calculations.

6. Click Calculate: Press the Calculate button to instantly compute all pagination values. The summary cards display total pages, the current item range (e.g., items 21–30), and the previous/next page numbers so you can verify navigation logic at a glance.

7. Switch Between Pagination Styles: Use the four tabs in the results panel to view parameters for each style:

   • Offset/Limit: Shows the computed offset and limit values, plus an example request URL using ?offset=N&limit=N query parameters.
   • Page-based: Shows the page and per_page parameters used by APIs like GitHub and many Laravel or Rails backends.
   • Cursor: Shows base64-encoded cursor tokens for current, previous, and next pages — useful for keyset/cursor-based pagination that avoids offset drift on live data.
   • Headers: Displays the full set of response headers including X-Total-Count, X-Total-Pages, X-Page, X-Per-Page, and the RFC 5988 Link header with first/prev/next/last relations.

8. Copy Values: Hover over any code block to reveal the copy button, or click the inline copy icon next to cursor values. Use these to paste directly into your API implementation, documentation, or test suite.

Common Use Cases:

• REST API implementation: Determine correct offset and limit values when building paginated list endpoints.
• API documentation: Generate accurate example URLs and response headers for your OpenAPI/Swagger docs.
• Frontend integration: Verify that your UI correctly computes page numbers and knows when to disable prev/next buttons.
• Testing and QA: Generate expected header values to assert against in integration tests.
• Cursor migration: Understand cursor tokens when migrating from offset-based to cursor-based pagination.
• Client SDK development: Reference correct query parameter names and header conventions for SDK wrappers.
• Debugging pagination bugs: Quickly recalculate expected values to compare against actual API responses.

Tips and Best Practices:

• Offset/limit pagination is simple but degrades on very large datasets or frequently-changing data — consider cursors for feeds or timelines.
• Cursor pagination avoids the "missing items" problem when records are inserted or deleted between page requests.
• The Link header follows RFC 5988 and is the standard used by GitHub, GitLab, and many other APIs — prefer it over custom pagination headers when possible.
• X-Total-Count is widely supported but can be expensive on large tables; consider making it optional or cached.
• Always validate that (page - 1) * pageSize does not exceed total items to avoid returning empty pages.
• Use consistent casing for query parameters (?page vs ?Page) and document your convention in your API spec.
• Page size limits (e.g., max 100) should be enforced server-side to prevent abuse.
• When using cursor pagination, encode the cursor as opaque base64 to allow changing the internal representation without breaking clients.