Azure Cosmos DB Best Practices

Comprehensive performance optimization guide for Azure Cosmos DB applications, containing 73+ rules across 10 categories, prioritized by impact to guide automated refactoring and code generation.

73 individual rule files are in the rules/ directory, one file per rule, synced from the AzureCosmosDB/cosmosdb-agent-kit. Load only the relevant rule file(s) when answering a question — do NOT load all files at once. Run /azure-cosmos-db-assistant:generate-skills to sync with the latest rules from the agent-kit.

When to Apply

Reference these guidelines when:

• Designing data models for Cosmos DB
• Choosing partition keys
• Writing or optimizing queries
• Implementing SDK patterns
• Reviewing code for performance issues
• Configuring throughput and scaling
• Building globally distributed applications
• Implementing vector search and RAG patterns

Rule Index

Rules are grouped by category prefix. For a given question, load files matching the relevant prefix (e.g., model-*.md for data modeling, sdk-*.md for SDK usage). See rules/_sections.md for category descriptions.

1. Data Modeling — CRITICAL (prefix: model-)

• model-embed-related.md — Embed related data retrieved together
• model-reference-large.md — Reference data when items grow large
• model-avoid-2mb-limit.md — Keep items well under 2MB limit
• model-id-constraints.md — Follow ID value length and character constraints
• model-nesting-depth.md — Stay within 128-level nesting depth limit
• model-numeric-precision.md — Understand IEEE 754 numeric precision limits
• model-denormalize-reads.md — Denormalize for read-heavy workloads
• model-schema-versioning.md — Version your document schemas
• model-type-discriminator.md — Use type discriminators for polymorphic data
• model-json-serialization.md — Handle JSON serialization correctly
• model-relationship-references.md — Use ID references with transient hydration

2. Partition Key Design — CRITICAL (prefix: partition-)

• partition-high-cardinality.md — Choose high-cardinality partition keys
• partition-avoid-hotspots.md — Distribute writes evenly
• partition-hierarchical.md — Use hierarchical partition keys for flexibility
• partition-query-patterns.md — Align partition key with query patterns
• partition-synthetic-keys.md — Create synthetic keys when needed
• partition-key-length.md — Respect partition key value length limits
• partition-20gb-limit.md — Plan for 20GB logical partition limit

3. Query Optimization — HIGH (prefix: query-)

• query-avoid-cross-partition.md — Minimize cross-partition queries
• query-use-projections.md — Project only needed fields
• query-pagination.md — Use continuation tokens for pagination
• query-avoid-scans.md — Avoid full container scans
• query-parameterize.md — Use parameterized queries
• query-order-filters.md — Order filters by selectivity

4. SDK Best Practices — HIGH (prefix: sdk-)

• sdk-singleton-client.md — Reuse CosmosClient as singleton
• sdk-async-api.md — Use async APIs for throughput
• sdk-retry-429.md — Handle 429s with retry-after
• sdk-connection-mode.md — Use Direct mode for production
• sdk-preferred-regions.md — Configure preferred regions
• sdk-excluded-regions.md — Exclude regions experiencing issues
• sdk-availability-strategy.md — Configure availability strategy for resilience
• sdk-circuit-breaker.md — Use circuit breaker for fault tolerance
• sdk-diagnostics.md — Log diagnostics for troubleshooting
• sdk-serialization-enums.md — Serialize enums as strings not integers
• sdk-emulator-ssl.md — Configure SSL and connection mode for Cosmos DB Emulator
• sdk-etag-concurrency.md — Use ETags for optimistic concurrency
• sdk-java-content-response.md — Enable content response on write operations (Java)
• sdk-java-cosmos-config.md — Configure Cosmos DB in Spring Boot with dependent beans
• sdk-java-spring-boot-versions.md — Match Java version to Spring Boot requirements
• sdk-local-dev-config.md — Configure local development to avoid cloud conflicts
• sdk-newtonsoft-dependency.md — Explicitly reference Newtonsoft.Json package (.NET)
• sdk-spring-data-annotations.md — Annotate entities for Spring Data Cosmos
• sdk-spring-data-repository.md — Use CosmosRepository correctly

5. Indexing Strategies — MEDIUM-HIGH (prefix: index-)

• index-exclude-unused.md — Exclude paths never queried
• index-composite.md — Use composite indexes for ORDER BY
• index-spatial.md — Add spatial indexes for geo queries
• index-range-vs-hash.md — Choose appropriate index types
• index-lazy-consistent.md — Understand indexing modes

6. Throughput & Scaling — MEDIUM (prefix: throughput-)

• throughput-autoscale.md — Use autoscale for variable workloads
• throughput-right-size.md — Right-size provisioned throughput
• throughput-serverless.md — Consider serverless for dev/test
• throughput-burst.md — Understand burst capacity
• throughput-container-vs-database.md — Choose allocation level wisely

7. Global Distribution — MEDIUM (prefix: global-)

• global-multi-region.md — Configure multi-region writes
• global-consistency.md — Choose appropriate consistency level
• global-conflict-resolution.md — Implement conflict resolution
• global-failover.md — Configure automatic failover
• global-read-regions.md — Add read regions near users
• global-zone-redundancy.md — Enable zone redundancy for HA

8. Monitoring & Diagnostics — LOW-MEDIUM (prefix: monitoring-)

• monitoring-ru-consumption.md — Track RU consumption
• monitoring-latency.md — Monitor P99 latency
• monitoring-throttling.md — Alert on throttling
• monitoring-azure-monitor.md — Integrate Azure Monitor
• monitoring-diagnostic-logs.md — Enable diagnostic logging

9. Design Patterns — HIGH (prefix: pattern-)

• pattern-change-feed-materialized-views.md — Use Change Feed for materialized views
• pattern-efficient-ranking.md — Use count-based or cached approaches for ranking
• pattern-service-layer-relationships.md — Use a service layer to hydrate document references

10. Vector Search — HIGH (prefix: vector-)

• vector-enable-feature.md — Enable vector search feature on account
• vector-embedding-policy.md — Define vector embedding policy on container
• vector-index-type.md — Configure vector indexes (QuantizedFlat or DiskANN)
• vector-distance-query.md — Use VectorDistance() for similarity search
• vector-normalize-embeddings.md — Normalize embeddings for cosine similarity
• vector-repository-pattern.md — Implement repository pattern for vector search

How to Use

Each rule is a separate file under rules/. When answering a Cosmos DB question, read only the relevant rule file(s) based on the prefix matching the topic:

• Data modeling question → read rules/model-*.md files
• Partition key question → read rules/partition-*.md files
• SDK/client question → read rules/sdk-*.md files
• etc.

Each rule file contains:

• Brief explanation of why it matters
• Incorrect code example with explanation
• Correct code example with explanation
• Additional context and references

Source: AzureCosmosDB/cosmosdb-agent-kit