langcore-rag 1.0.4

RAG query parsing plugin — parse natural language queries into semantic terms and structured filters using LLMs

LangCore RAG — Query Parsing for Hybrid Retrieval

A plugin for LangCore that parses natural-language queries into semantic terms (for vector search) and structured metadata filters (for database / index filtering), enabling hybrid RAG retrieval pipelines. Inspired by LangStruct's .query() method.

Note: This is a third-party plugin for LangCore. For the main LangCore library, visit google/langcore.

Installation

Install from source:

git clone <repo-url>
cd langcore-rag
pip install -e .

Or with uv:

uv pip install -e .

Features at a Glance

Feature	langcore-rag	LangStruct
Query → semantic terms + filters	✅ QueryParser.parse()	✅ .query()
Async support	✅ async_parse()	✅
Pydantic schema introspection	✅ Auto-discovers filterable fields	✅
MongoDB-style operators	✅ $eq, $gte, $lte, $in, $nin, etc.	✅
Confidence score	✅ 0.0 – 1.0	❌
Explanation / rationale	✅ Human-readable	❌
Any LLM backend	✅ Via LiteLLM (100+ providers)	✅
Robust JSON parsing	✅ Raw JSON + Markdown fences + graceful fallback	⚠️

Quick Start

1. Define a Schema

from pydantic import BaseModel, Field

class Invoice(BaseModel):
    amount: float = Field(description="Total invoice amount in USD")
    due_date: str = Field(description="Due date in ISO-8601 format")
    vendor: str = Field(description="Vendor / supplier name")
    paid: bool = Field(description="Whether the invoice is paid")

2. Parse a Query

from langcore_rag import QueryParser

parser = QueryParser(schema=Invoice, model_id="gemini/gemini-2.5-flash")
parsed = parser.parse("invoices over $5000 due in March 2024")

print(parsed.semantic_terms)
# → ["invoices"]

print(parsed.structured_filters)
# → {"amount": {"$gte": 5000}, "due_date": {"$gte": "2024-03-01", "$lte": "2024-03-31"}}

print(parsed.confidence)
# → 0.92

print(parsed.explanation)
# → "Extracted amount ≥ 5000 and date range for March 2024."

3. Async Usage

import asyncio
from langcore_rag import QueryParser

async def main():
    parser = QueryParser(schema=Invoice, model_id="gpt-4o")
    parsed = await parser.async_parse("unpaid invoices from Acme Corp")
    print(parsed.structured_filters)
    # → {"paid": {"$eq": false}, "vendor": {"$eq": "Acme Corp"}}

asyncio.run(main())

API Reference

QueryParser

QueryParser(
    schema: type[BaseModel],
    model_id: str,
    *,
    temperature: float = 0.0,
    max_tokens: int = 1024,
    **litellm_kwargs,
)

Parameter	Type	Description
schema	type[BaseModel]	Pydantic model whose fields define filterable metadata
model_id	str	Any LiteLLM-compatible model ID (e.g. "gpt-4o", "gemini/gemini-2.5-flash", "anthropic/claude-3-opus")
temperature	float	Sampling temperature (default 0.0 for deterministic output)
max_tokens	int	Maximum tokens to generate (default 1024)
**litellm_kwargs		Extra kwargs forwarded to litellm.completion() (e.g. api_key, api_base, timeout)

Methods

Method	Signature	Description
parse	(query_text: str) -> ParsedQuery	Synchronous query parsing
async_parse	(query_text: str) -> ParsedQuery	Asynchronous query parsing

Properties

Property	Type	Description
schema	type[BaseModel]	The Pydantic schema used for field discovery
model_id	str	The LiteLLM model identifier
system_prompt	str	The generated system prompt (useful for debugging)

ParsedQuery

An immutable (frozen) dataclass returned by parse() / async_parse().

Field	Type	Description
semantic_terms	list[str]	Free-text terms for vector / similarity search
structured_filters	dict[str, Any]	Metadata filters with MongoDB-style operators
confidence	float	0.0 – 1.0 confidence in the parse quality
explanation	str	Human-readable rationale for the decomposition

How It Works

1. Schema introspection — QueryParser inspects the Pydantic model's fields to identify which ones are scalar/filterable (int, float, str, bool, date, datetime). Complex types like list[str] are excluded.

2. System prompt generation — A system prompt is built listing the filterable fields with their types and descriptions, instructing the LLM to output a JSON object with semantic_terms, structured_filters, confidence, and explanation.

3. LLM call — The query text is sent as a user message alongside the system prompt via litellm.completion() (sync) or litellm.acompletion() (async).

4. Response parsing — The LLM's text response is parsed as JSON (handling both raw JSON and Markdown code fences). Values are type-coerced and clamped to produce a valid ParsedQuery.

Supported Filter Operators

The parser instructs the LLM to use MongoDB-style operators:

Operator	Meaning	Example
$eq	Equals	{"vendor": {"$eq": "Acme"}}
$ne	Not equals	{"paid": {"$ne": true}}
$gt	Greater than	{"amount": {"$gt": 1000}}
$gte	Greater than or equal	{"amount": {"$gte": 5000}}
$lt	Less than	{"amount": {"$lt": 100}}
$lte	Less than or equal	{"due_date": {"$lte": "2024-12-31"}}
$in	In list	{"vendor": {"$in": ["Acme", "Globex"]}}
$nin	Not in list	{"vendor": {"$nin": ["Initech"]}}

Development

# Install dev dependencies
uv sync

# Run tests
uv run pytest tests/ -v

# Lint
uv run ruff check langcore_rag/ tests/

# Format
uv run ruff format langcore_rag/ tests/

License

Apache 2.0