STAC API - Collection Search Endpoint

• Title: Collection Search Endpoint
• Conformance Classes:
  • https://api.stacspec.org/v1.0.0-beta.1/collection-search-endpoint
• Scope: STAC API - Core
• Extension Maturity Classification: Proposal
• Dependencies:
  • STAC API - Core
  • STAC API - Collection Search
• Owner: @jonhealy1

Introduction

This extension defines a dedicated Collection Search endpoint (/collections-search) that supports both GET and POST methods.

It provides a safe, conflict-free mechanism to perform advanced searching (filtering, sorting) on Collections without colliding with the Transaction Extension on the root /collections path.

Motivation

The standard STAC API - Collection Search extension relies on the /collections endpoint. While this works well for simple GET requests, it introduces a significant architectural conflict when POST is required for advanced search (e.g., complex CQL filters or large bodies).

As noted in the official Collection Search documentation:

"STAC may add behavior for POST /collections in the future, but due to a potential conflict with the Transaction Extension, specific rules for content negotiation might be required."

In practice, implementing Content-Type negotiation to distinguish between "Creating a Collection" (Transaction) and "Searching Collections" (Search) on the same URL (POST /collections) is difficult for many API frameworks and confusing for client libraries.

This extension resolves the conflict by moving search operations to a dedicated resource: /collections-search.

Endpoints

Method	URI	Description
GET	/collections-search	Simple Search. Retrieves collections matching query parameters. Functionally identical to GET /collections.
POST	/collections-search	Advanced Search. Retrieves collections matching the JSON body filter.

Query Parameters and Fields

This extension supports all query parameters and extension behaviors defined in the standard Collection Search specification, including:

• Filter (CQL2)
• Sort
• Fields
• Free-Text Search (q)

GET Request

Behaves exactly like the standard GET /collections endpoint, accepting parameters via the URL.

GET /collections-search?limit=10&q=sentinel&sortby=-id

POST Request

Accepts a JSON body containing search parameters. This allows for complex queries that exceed URL length limits or require structured data.

Header: Content-Type: application/json

Body Schema:

{
  "q": ["sentinel", "radar"],
  "datetime": "2020-01-01/2021-01-01",
  "limit": 10,
  "sortby": [
    { "field": "id", "direction": "desc" }
  ],
  "filter": {
    "op": "and",
    "args": [
      { "op": "=", "args": [{ "property": "platform" }, "sentinel-1"] }
    ]
  }
}

Response

The response format for both GET and POST is a standard STAC Collections object.

{
  "collections": [
    {
      "type": "Collection",
      "id": "sentinel-1-grd",
      "stac_version": "1.0.0",
      "description": "Sentinel-1 Ground Range Detected",
      "links": [],
      "extent": {
        "spatial": { "bbox": [[-180, -90, 180, 90]] },
        "temporal": { "interval": [["2014-10-03T00:00:00Z", null]] }
      }
    }
  ],
  "links": [
    {
      "rel": "root",
      "href": "https://api.example.com/"
    },
    {
      "rel": "self",
      "href": "https://api.example.com/collections-search"
    }
  ]
}

Relation to Item Search

This endpoint mirrors the design pattern of Item Search, creating symmetry in the API:

Resource	Simple Search (GET)	Advanced Search (POST)
Items	/search	/search
Collections	/collections-search	/collections-search