The short answer
Blinkit doesn't publish a public API that gives market data: competitors' ranks, prices, stock or sales. What it gives brands is their own data, through the seller portal and the ads console, mostly as on-screen reports and downloads.
So "a Blinkit data API" usually means one of two things, and they have different answers.
Option 1: your own data, from Blinkit's portals
What you get: your sales, inventory and ad performance.
How: the Blinkit seller portal and ads console. Both offer reports you can download. Some teams download them on a schedule and load them into their own sheets or BI tools.
Good for: exact numbers on what you sold, what you hold and what you spent.
Limits: it shows only your brand. It doesn't show where you rank next to competitors, or the shelf a shopper sees in a given dark store. If you want more than the portals offer, ask your Blinkit account team; don't assume an integration exists.
Option 2: market data, from tracking the public shelf
What you get: search results by keyword and rank (organic and sponsored apart), availability by dark store, prices and discounts, and estimated sales by product, brand and category.
How: someone has to read the Blinkit shelf every day, across many cities and dark stores, because each store has its own results. You can build that yourself or use a managed service.
Building it yourself means many locations, every day, plus constant upkeep as the app changes, plus checking the platform's terms. It is a real engineering project, not a script.
A managed service such as Netr's Digital Shelf does the tracking and gives you the result, set up for your SKUs, competitors, keywords and cities, updated every morning.
Limits: market sales from shelf tracking are estimates, reliable as shares and trends rather than exact counts.
Which one you need
Most brands need both. Your own data tells you what happened. Market data tells you why: you went out of stock in busy stores, a competitor cut price, or someone outbid you on the first scroll. Netr puts both side by side when you connect your seller account; the market view works without it.
See Blinkit data: what exists, Blinkit sales data and what Netr tracks in Blinkit data.