MongoDB Atlas: create a Vector Search index that actually works

TL;DR

Use mongosh, a driver, or the Atlas UI (Search tab, JSON editor). The definition shape: `js db.docs.createSearchIndex("vec\_idx", "vectorSearch", { fields: [ { type: "vector", path: "embedding", numDimensions: 1536, similarity: "cosine" }, { type: "filter", path: "tenantId" } ] });

Steps

1. Use mongosh, a driver, or the Atlas UI (Search tab, JSON editor). The definition shape:

db.docs.createSearchIndex("vec_idx", "vectorSearch", {
 fields: [
 { type: "vector", path: "embedding", numDimensions: 1536, similarity: "cosine" },
 { type: "filter", path: "tenantId" }
 ]
});

When to use

You are seeing this: The definition shape: `js db.docs.createSearchIndex("vec\_idx", "vectorSearch", { fields: [ { type: "vector", path: "embedding", numDimensions: 1536, similarity: "cosine" }, { type: "filter", path: "tenantId" } ] }); ` Use this skill when you run into "MongoDB Atlas: create a Vector Search index that actually works".

When not to use

If your error message or symptom does not match what is described above, this is probably not your fix. Search for your exact error text instead of forcing this one to fit.

Versions

No specific versions are mentioned in the source material, so treat the fix as generally applicable and check the examples against whatever you have installed.

Why this happens

The original report does not dig into a root cause. It documents the symptom and the fix that resolved it.

Vector search index definition (type vectorSearch, fields with type vector and filter, numDimensions, similarity options) and the READY status requirement verified against current MongoDB Atlas Search documentation, including https://www.mongodb.com/docs/search/indexes/manage-indexes/, on 2026-09-26.