haiku.rag/docs/capabilities/index.md

# Capabilities

haiku.rag provides native [Pydantic AI capabilities](https://ai.pydantic.dev/capabilities/):

| Capability | Use it for |
|---|---|
| [`RAGCapability`](rag.md) | Grounded document search and citations. |
| [`AnalysisCapability`](analysis.md) | Corpus computation and structural analysis with sandboxed Python. |
| [`EvidenceCompactionCapability`](compaction.md) | Optional. Shrinking a conversation's history to the evidence that was cited. |
| [`CitationPolicyCapability`](policy.md) | Optional. Requiring every answer to declare what grounds it. |

The two evidence capabilities are deferred by default. An agent initially sees only their descriptions and the standard `load_capability` tool. Instructions and tools enter the model context only when the model loads a capability.

## Compose an agent

Pick one evidence capability, and add both optional capabilities to it:

```python
from dataclasses import dataclass, field
from typing import Any

from pydantic_ai import Agent
from pydantic_ai.messages import ModelMessage

from haiku.rag.capabilities.compaction import create_capability as compaction
from haiku.rag.capabilities.policy import create_capability as citation_policy
from haiku.rag.capabilities.rag import create_capability as rag


@dataclass
class Deps:
    state: dict[str, Any] = field(default_factory=dict)


agent = Agent(
    "openai:gpt-5",
    capabilities=[
        rag(db_path="my.lancedb"),
        compaction(),
        citation_policy(),
    ],
    deps_type=Deps,
)

# One Deps and one history for the conversation: the capabilities read both.
deps = Deps()
history: list[ModelMessage] = []

result = await agent.run("What does the knowledge base say about X?", deps=deps, message_history=history)
history = list(result.all_messages())
print(result.output)
```

!!! warning "Both optional capabilities need the host to carry state"

    They read what earlier questions retrieved and cited from the capability's
    state, so the host must expose a `state` dict on its agent dependencies and
    hand the same dict back on every run of a conversation, alongside the message
    history. With only the message history, every run starts from an empty record:
    compaction refuses rather than replace evidence it cannot retain, and the
    citation policy cannot enforce a follow-up about evidence cited earlier.

Swap `rag` for `analysis` for an analysis agent. Both optional capabilities work the
same way with either one, and neither exposes tools or takes configuration.

!!! note "Register one evidence capability, not both"

    `RAGCapability` and `AnalysisCapability` overlap. Both search the same corpus and
    both register citations, so an agent holding both must choose between two
    near-identical search tools, and its citations land in whichever capability it
    happened to call. Each also carries its own request limit and its own search
    budget, so registering both doubles what a question may spend.

    Choose by what the questions need. `RAGCapability` answers questions from retrieved
    passages. `AnalysisCapability` adds a Python sandbox and a document filesystem, for
    questions that compute over many documents or read their structure, and it can
    search too. If you need computation, register the analysis capability alone rather
    than adding it to the RAG one.

## Agent specs

The capabilities can be declared in a Pydantic AI [agent spec](https://ai.pydantic.dev/agent-spec/):

```yaml title="agent.yaml"
model: openai:gpt-5
instructions: You are a research assistant with access to a document knowledge base.
capabilities:
  - RAGCapability:
      db_path: /data/kb.lancedb
      defer_loading: false
  - EvidenceCompactionCapability
  - CitationPolicyCapability
```

Pydantic AI does not discover third-party capabilities, so the caller names the classes:

```python
from pydantic_ai import Agent

from haiku.rag.capabilities.compaction import EvidenceCompactionCapability
from haiku.rag.capabilities.policy import CitationPolicyCapability
from haiku.rag.capabilities.rag import RAGCapability

agent = Agent.from_file(
    "agent.yaml",
    deps_type=Deps,
    custom_capability_types=[
        RAGCapability,
        EvidenceCompactionCapability,
        CitationPolicyCapability,
    ],
)
```

`deps_type` stays a Python argument, since the capabilities read and write their state
through `deps.state` (see [State](#state)). `Agent.from_file` reads YAML, which needs
`pydantic-ai-slim[spec]`; `Agent.from_spec` takes a dict and needs no YAML parser.

Set `defer_loading: false` when the agent registers a single evidence capability, so its
tools are visible immediately. Leave it at the default when the model should route among
multiple capabilities.

A `config:` block accepts a whole `AppConfig`, for agents in one process that need
different databases or embedding models:

```yaml
capabilities:
  - RAGCapability:
      db_path: /data/kb.lancedb
      config:
        embeddings:
          model: {provider: ollama, name: embeddinggemma, vector_dim: 2048}
```

The block is read like a `haiku.rag.yaml` file: keys it omits take `AppConfig` defaults
rather than values from the configuration file on disk. The embedding model must match the
database; a mismatch may prevent opening it or produce invalid retrieval. Write the block in
full or omit it and let the [configuration file](../configuration/index.md) apply.

## State

Capabilities use a plain `state: dict[str, Any]` attribute on agent dependencies when one is available. RAG state lives under `"rag"`; analysis state lives under `"analysis"`. This keeps state independent of any transport or UI protocol.

Applications serving AG-UI should adapt the agent with Pydantic AI's `AGUIAdapter`. Native model and tool events require no haiku.rag-specific bridge.

## Database Selection

RAG and analysis capabilities cover the databases the configuration places: [`lancedb.databases`](../configuration/storage.md#multiple-databases), or with nothing configured the default database `haiku.rag` under `storage.data_dir`. The `db_path` argument, or `HAIKU_RAG_DB`, places one database where the configuration places none; beside `lancedb.databases` either raises `AmbiguousDatabaseError`.

Passing a client through `rag=` bypasses this selection. The capability uses the databases covered by that client and does not close it.