mongo-index

Use when a MongoDB query or aggregation is slow, when explain shows COLLSCAN or an in-memory sort, or when designing indexes for a collection.

Skill by Srimukh99

IndexedMIT

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Works with Claude Code, Claude apps, Codex, Cursor, Gemini CLI, GitHub Copilot, VS Code, OpenCode, Goose, Windsurf. Read the repository before you give any tool access to your data.

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About

Use when a MongoDB query or aggregation is slow, when explain shows COLLSCAN or an in-memory sort, or when designing indexes for a collection.

Use cases: data

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What this skill can do and what it asks for, from its SKILL.md. Checked Oct 25, 2026.

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codeload.github.com · found in install command

Files it touches

~/.claude/skills/mongo-index

What's inside

Skill name: mongo-index
Description: Use when a MongoDB query or aggregation is slow, when explain shows COLLSCAN or an in-memory sort, or when designing indexes for a collection.
License: MIT
Instructions: 30 lines in SKILL.md · view on GitHub

Files (1)

SKILL.md

SKILL.md (first lines)

# mongo-index

## 1. Measure

`db.coll.find(<filter>).sort(<sort>).explain("executionStats")`, or `.explain()` on the aggregate. Look at:

- `totalDocsExamined` vs `nReturned`: far above 1:1 means wasted work.
- A `COLLSCAN` stage on a large collection.
- A brubricg `SORT` stage (sorting in memory).

## 2. Design the index (Equality, Sort, Range)

Order compound index fields: equality matches first, then sort fields, then range filters. Example: filter `{status: "open", created: {$gt: d}}` sorted by `priority` → index `{status: 1, priority: 1, created: 1}`.

## 3. Sharpen it

- **Covered queries**: project only indexed fields (and exclude `_id` if not in the index) so documents are never fetched.
- **Partial indexes** when queries always target a subset (`{status: "open"}`).
- **TTL indexes** for data that should expire.
- **Aggregations**: put `$match` and `$sort` first so they can use an index; `$lookup` on a large collection needs an index on the foreign field.

## 4. Keep the set healthy

Every index slows writes and uses memory. Use `$indexStats` to find unused indexes and remove them after confirming with the owners. Build new indexes on large production collections during low traffic and watch replication lag.

## Prove it

Report `executionTimeMillis` and `totalDocsExamined` before and after (`ship`).

From Srimukh99/rubric, MIT.

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Last commit (this folder): Oct 2, 2026 (26 days ago)

From GitHub (fetched Oct 24, 2026).

Details

License: MIT
Repository: github.com/Srimukh99/rubric
First seen: Oct 24, 2026
Last checked: Oct 24, 2026
Source: GitHub github-graphql

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mongo-index skill. Agent Mart. https://agentmart.dev/skills/srimukh99-mongo-index (last updated 2026-10-24)