I'm trying to build one search layer across multiple internal apps. What should I use?

If you want one search layer across multiple internal apps, the best choice depends on whether you want:

1. A single search box across everything
2. A unified search index with connectors
3. A customizable product-search style experience
4. A self-hosted / cloud-managed enterprise search stack

Best options by use case

1) If you want a ready-made internal search platform

Use Elasticsearch / OpenSearch.

• Good for indexing data from many apps
• Flexible relevance tuning
• Supports search APIs, filtering, faceting, autocomplete
• Can be self-hosted or managed
• Works well if your team can build the ingestion/indexing pipeline

Best when: you need control and have engineering resources.

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2) If you want a modern SaaS-like internal enterprise search

Use Glean, Coveo, or Algolia NeuralSearch / Algolia Search depending on your needs.

• Glean is especially strong for internal knowledge across apps like Slack, Google Drive, Jira, Confluence, etc.
• Coveo is strong for enterprise relevance and connectors
• Algolia is great for fast, developer-friendly search, but often more product/app search oriented than broad enterprise search

Best when: you want speed to value and lots of built-in connectors.

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3) If you want to build the layer yourself on top of multiple systems

Use a central search service with:

• ingestion/connectors
• normalization layer
• index (OpenSearch/Elasticsearch)
• query API
• permissions-aware filtering

This is the most common architecture if you have multiple internal apps and specific access-control needs.

Best when: you have unique business logic or strict ACL requirements.

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My practical recommendation

• For internal company-wide search: Glean if you want turnkey, or OpenSearch/Elasticsearch if you want to own the stack.
• For search embedded into your own app(s): Algolia.
• For Microsoft-heavy environments: consider Microsoft Search / SharePoint / Graph connectors.
• For Google Workspace-heavy environments: consider Google Cloud Search.

Important thing to get right

Regardless of the tool, make sure you handle:

• document/user permissions
• sync latency
• schema normalization across apps
• deduplication
• ranking/relevance tuning
• auditability

If you want a simple answer

• Fastest to deploy: Glean
• Most control: OpenSearch / Elasticsearch
• Best for app search UX: Algolia

If you tell me:

• what internal apps you have,
• whether you need permissions-aware search,
• cloud vs self-hosted,
• and how many users/docs,

I can recommend a specific architecture and tool choice.