AGENTS.md — Milvus

Milvus is an open-source vector database for similarity search, hybrid search, and RAG. You interact with it through the PyMilvus SDK’s MilvusClient interface. Copy the full prompt below into your AI tool to apply these rules automatically. For detailed task-specific prompts, see AI Prompts.

How to use this prompt

1. Copy the full prompt from the Full prompt section below.
2. Save it to the location your AI tool expects — see the environment table for placement details.
3. Your AI assistant will automatically apply these rules when generating or reviewing Milvus code.

For Cursor users: copy the prompt from the Full prompt section and save it under .cursor/rules/ in your project.

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# AGENTS.md — Milvus

Milvus is an open-source vector database for similarity search, hybrid search, and RAG. You interact with it through the PyMilvus SDK's `MilvusClient` interface.

Use these rules whenever you generate, review, or debug code that connects to Milvus or Zilliz Cloud.

## Client & connection

1. **CRITICAL — Always use `MilvusClient`.** Never use the legacy ORM API (`connections.connect()`, `Collection()`, `utility.list_collections()`). The ORM API is deprecated and will be removed. If the user provides ORM code, rewrite it to `MilvusClient`.

2. **Connection patterns.** Local unauthenticated: `uri` only. Zilliz Cloud or authenticated Milvus: `uri` + `token`.

```python
# Local Milvus
client = MilvusClient(uri="http://localhost:19530")

# Zilliz Cloud / authenticated Milvus
client = MilvusClient(uri="YOUR_MILVUS_URI", token="YOUR_MILVUS_TOKEN")
```

## Schema & data

3. **CRITICAL — Use `DataType` enum, not strings.** Write `DataType.FLOAT_VECTOR`, not `"FLOAT_VECTOR"`.

4. **CRITICAL — Schema is immutable in v2.5.x and earlier.** You cannot add, modify, or delete fields after creation — drop and recreate the collection. In v2.6+, you can add new nullable fields with `add_collection_field()` but still cannot modify or delete existing fields.

5. **Primary keys: `INT64` or `VARCHAR` only.** Composite primary keys are not supported. Primary keys must be unique across the entire collection, including across partitions.

6. **Use `upsert()` to update entities.** There is no `client.update()` method. `upsert()` replaces the entire entity if the primary key exists, or inserts a new one. Use `insert()` only when you are certain there are no primary key conflicts.

7. **BM25 must be defined at collection creation time.** The BM25 function and text analyzer cannot be added to an existing collection.

## Index & loading

8. **CRITICAL — Index before load, load before search.** A vector field must have an index before the collection can be loaded. A collection must be loaded before any search or query. Shortcut: pass both `schema` and `index_params` to `create_collection()` and Milvus handles index creation and loading automatically.

9. **Start with `AUTOINDEX`.** Use `index_type="AUTOINDEX"` unless you have specific requirements. Choose HNSW for high recall, DiskANN for larger-than-RAM datasets, IVF_FLAT for memory-constrained scenarios.

## Search

10. **CRITICAL — One vector per `AnnSearchRequest`.** Each sub-request in a hybrid search accepts exactly one query vector. Do not pass a list of multiple vectors.

11. **One ranker per `hybrid_search()` call.** You cannot chain `WeightedRanker` and `RRFRanker` together. Pick one.

## Quick start

```python
from pymilvus import MilvusClient, DataType

client = MilvusClient(uri="http://localhost:19530")

# 1. Define schema
schema = client.create_schema(auto_id=True)
schema.add_field("id", DataType.INT64, is_primary=True)
schema.add_field("vector", DataType.FLOAT_VECTOR, dim=768)
schema.add_field("text", DataType.VARCHAR, max_length=512)

# 2. Define index
index_params = client.prepare_index_params()
index_params.add_index(field_name="vector", index_type="AUTOINDEX", metric_type="COSINE")

# 3. Create collection (auto-indexes and auto-loads)
client.create_collection(collection_name="docs", schema=schema, index_params=index_params)

# 4. Insert
client.insert(collection_name="docs", data=[
    {"vector": [0.1] * 768, "text": "first doc"},
    {"vector": [0.2] * 768, "text": "second doc"},
])

# 5. Search
results = client.search(
    collection_name="docs",
    data=[[0.15] * 768],
    limit=5,
    output_fields=["text"],
)
```

## Common mistakes

| Mistake | Fix |
|---|---|
| Using `connections.connect()` / `Collection()` | Rewrite with `MilvusClient` |
| Calling `client.search()` before loading | Pass `index_params` to `create_collection()`, or call `create_index()` then `load_collection()` first |
| Multiple vectors in one `AnnSearchRequest` | One vector per sub-request; create multiple `AnnSearchRequest` objects |
| Calling `client.update()` | Use `client.upsert()` |
| Adding BM25 after collection exists | Define BM25 function and analyzer at `create_collection()` time |
| String field types (`"FLOAT_VECTOR"`) | Use `DataType.FLOAT_VECTOR` from the enum |