feat: add ability to create atlas search indexes MCP-275 #692

nirinchev · 2025-10-27T15:11:45Z

Proposed changes

This adds support for creating atlas search indexes. Dropping and listing is already supported, so needed no changes.

Copilot

Pull Request Overview

This PR adds support for creating Atlas Search (lexical) indexes through the MCP server. The changes enable users to create Atlas Search indexes with both dynamic and explicit field mappings, complementing the existing support for listing and dropping search indexes.

Key changes:

Added Atlas Search index creation support to create-index tool with comprehensive schema validation
Enhanced testing to differentiate between search and vector search indexes
Added accuracy tests for various Atlas Search index creation scenarios

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
`src/tools/mongodb/create/createIndex.ts`	Adds `atlasSearchIndexDefinition` schema and implements search index creation logic
`tests/integration/tools/mongodb/create/createIndex.test.ts`	Adds comprehensive integration tests for Atlas Search index creation scenarios
`tests/integration/tools/mongodb/delete/dropIndex.test.ts`	Refactors tests to handle both search and vector search indexes separately
`tests/accuracy/createIndex.test.ts`	Adds accuracy test cases for Atlas Search index creation with various configurations
`tests/accuracy/sdk/accuracyTestingClient.ts`	Removes deprecated `--connectionString` flag from CLI arguments
`README.md`	Updates documentation to remove deprecated `--connectionString` flag

Comments suppressed due to low confidence (1)

tests/integration/tools/mongodb/create/createIndex.test.ts:1

The index names are being evaluated at test definition time rather than test execution time. If getSearchIndexName() and getVectorIndexName() depend on beforeEach setup, these calls will execute before the setup runs, potentially returning undefined or stale values. Wrap these in functions: { description: "search", indexName: () => getSearchIndexName() } and update the test to call the function.

import { describeWithMongoDB, validateAutoConnectBehavior, waitUntilSearchIsReady } from "../mongodbHelpers.js";

src/tools/mongodb/create/createIndex.ts

tests/integration/tools/mongodb/delete/dropIndex.test.ts

coveralls · 2025-10-27T16:15:44Z

Pull Request Test Coverage Report for Build 18909991547

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

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For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

140 of 140 (100.0%) changed or added relevant lines in 1 file are covered.
57 unchanged lines in 2 files lost coverage.
Overall coverage increased (+0.2%) to 80.378%

Files with Coverage Reduction	New Missed Lines	%
src/tools/mongodb/read/aggregate.ts	26	88.72%
src/common/search/vectorSearchEmbeddingsManager.ts	31	81.79%

Totals
Change from base Build 18847594160:	0.2%
Covered Lines:	6435
Relevant Lines:	7861

💛 - Coveralls

nirinchev · 2025-10-28T10:39:42Z

src/tools/mongodb/create/createIndex.ts

 import { quantizationEnum, similarityEnum } from "../../../common/search/vectorSearchEmbeddingsManager.js";

 export class CreateIndexTool extends MongoDBToolBase {
-    private vectorSearchIndexDefinition = z.object({


This is best viewed with the "Hide whitespace" option - it's just prettier reformatting the indents.

nirinchev · 2025-10-28T10:45:51Z

tests/accuracy/sdk/accuracyTestingClient.ts

        });

-        const args = [MCP_SERVER_CLI_SCRIPT, "--connectionString", mdbConnectionString, ...additionalArgs];
+        const args = [MCP_SERVER_CLI_SCRIPT, mdbConnectionString, ...additionalArgs];


--connectionString is deprecated so using the positional argument.

kmruiz · 2025-10-30T12:58:16Z

src/tools/mongodb/create/createIndex.ts

+        })
+        .describe("Definition for a Vector Search index.");
+
+    private atlasSearchIndexDefinition = z


Why aren't we supporting custom analyzers?

https://www.mongodb.com/docs/atlas/atlas-search/analyzers/custom/

kmruiz · 2025-10-30T12:59:14Z

src/tools/mongodb/create/createIndex.ts

+    private atlasSearchIndexDefinition = z
+        .object({
+            type: z.literal("search"),
+            analyzer: z


Probably this should be an enum of the analyzers.

kmruiz · 2025-10-30T13:01:25Z

src/tools/mongodb/create/createIndex.ts

+                    "The analyzer to use for the index. Can be one of the built-in lucene analyzers (`lucene.standard`, `lucene.simple`, `lucene.whitespace`, `lucene.keyword`), a language-specific analyzer, such as `lucene.cjk` or `lucene.czech`, or a custom analyzer defined in the Atlas UI."
+                ),
+            mappings: z
+                .object({


Lack support of:

numPartitions

searchAnalyzer vs analyze

custom analyzers

storedSources

synonyms

typeSets

https://www.mongodb.com/docs/atlas/atlas-search/index-definitions/?deployment-type=atlas&interface=driver&language=nodejs#std-label-ref-index-definitions

We could say that custom analyzers are not that important, but storedSources is actually relevant most of the times.

The args shape is based on the POC the search team did for index support and I was going off of the assumption that they've selected the fields that they see the most value in exposing to LLMs. I realize there's a lot more configuration that's possible, I'm just not sure how much of that is stuff we expect agents to configure vs an actual human who wants to fine-tune the index.

A POC to see the feasibility to create search indexes and production code are likely to have different requirements.

kmruiz · 2025-10-30T13:30:22Z

src/tools/mongodb/create/createIndex.ts

+            mappings: z
+                .object({
+                    dynamic: z
+                        .boolean()


Dynamic can be an object of typeSets.

This is in preview though, so I don't expect there's sufficient docs or training data for general-purpose models to accurately choose which one to use.

The preview is for vector search though, FTS is explicitly out of scope of the vector search project.

The typeSets functionality is in preview.

kmruiz

The current implementation lacks support for multiple important fields, and it should be discussed if we want to support them or not.

kmruiz · 2025-10-30T13:34:15Z

src/tools/mongodb/create/createIndex.ts

+                            z.string().describe("The field name"),
+                            z
+                                .object({
+                                    type: z


Objects will require additional fields depending on the type. I know passthrough will keep them, but we should document them so the agent knows which ones to use and how. For example, autocomplete supports defining a custom analyzer, how to tokenize (which is really important) and similarity functions.

The exact shape is extremely complex to represent in a json schema. I'm worried that being overly specific will result in this being more harmful than helpful, especially if we expect the majority of the use cases to revolve around just specifying the type.

Yep, the schema is complicated, it has a lot of options that are not compatible even between them. We should have proper documentation of which ones we want to expose and which ones not, something that we haven't discussed yet because supporting the most used bits of Atlas Search is already a substantial effort.

nirinchev requested a review from a team as a code owner October 27, 2025 15:11

nirinchev requested a review from Copilot October 27, 2025 16:03

Base automatically changed from ni/feature-flags to main October 27, 2025 16:03

nirinchev added 2 commits October 27, 2025 17:04

add support for creating atlas search indexes

b63916e

add more tests

3fab3b7

nirinchev force-pushed the ni/atlas-search branch from e9cef48 to 3fab3b7 Compare October 27, 2025 16:04

Copilot AI reviewed Oct 27, 2025

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src/tools/mongodb/create/createIndex.ts Show resolved Hide resolved

src/tools/mongodb/create/createIndex.ts Show resolved Hide resolved

tests/integration/tools/mongodb/delete/dropIndex.test.ts Show resolved Hide resolved

tweak descriptions and errors

809aa9a

nirinchev commented Oct 28, 2025

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gagik approved these changes Oct 28, 2025

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nirinchev changed the title ~~feat: add ability to create atlas search indexes~~ feat: add ability to create atlas search indexes MCP-275 Oct 28, 2025

replace arg as a function

23d1a17

kmruiz reviewed Oct 30, 2025

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kmruiz requested changes Oct 30, 2025

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kmruiz reviewed Oct 30, 2025

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feat: add ability to create atlas search indexes MCP-275 #692

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nirinchev commented Oct 27, 2025

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coveralls commented Oct 27, 2025 •

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