llmbelt 0.2.0

A tiny, dependency-free tool belt for LLMs: token counting, cost estimation, retries, prompt templates, and text chunking.

llmbelt 🧰

A tiny, zero-dependency tool belt for working with LLMs. The small utilities you end up re-writing on every project — token counting, cost estimation, retries, prompt templates, and text chunking — in one clean import.

• 🪶 Zero required dependencies — pure standard library.
• 🔌 Provider-agnostic — works with Anthropic, OpenAI, Gemini, or anything else.
• 🧪 Fully tested across Python 3.9–3.12.

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Install

pip install llmbelt

# Optional: exact token counts for OpenAI-family models
pip install "llmbelt[tiktoken]"

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Usage

Count tokens

from llmbelt import count_tokens, truncate_to_tokens

count_tokens("Hello, world!")              # exact if tiktoken installed, else estimated
count_tokens("Hello", model="gpt-4o")      # use a model-specific encoding

# Trim text to fit a budget (great before sending context to an API)
truncate_to_tokens(long_document, max_tokens=4000)

Estimate cost

from llmbelt import estimate_cost, Price

estimate_cost(input_tokens=1_500, output_tokens=800, model="gpt-4o-mini")   # -> USD

# Bring your own prices (the built-in table is approximate — always verify):
my_prices = {"my-model": Price(input_per_1m=2.0, output_per_1m=6.0)}
estimate_cost(1000, 500, "my-model", pricing=my_prices)

Retry with backoff

from llmbelt import retry

@retry(attempts=5, exceptions=(ConnectionError, TimeoutError))
def call_api():
    ...   # retried with exponential backoff + jitter on failure

# Works on async functions too — awaited, with non-blocking asyncio.sleep backoff
@retry(attempts=5, exceptions=(ConnectionError, TimeoutError))
async def call_api_async():
    ...

Extract JSON from a model reply

from llmbelt import extract_json

extract_json('Sure!\n```json\n{"ok": true}\n```')   # -> {"ok": True}
extract_json('The score is {"value": 0.9}.')         # -> {"value": 0.9}
extract_json("no json here", default=None)           # -> None (else raises ValueError)

Prompt templates

from llmbelt import PromptTemplate

t = PromptTemplate("Translate {text} into {language}.")
t.render(text="hello", language="French")   # "Translate hello into French."
t.render(text="hello")                      # KeyError: Missing template variables: ['language']

Chunk text for RAG

from llmbelt import chunk_text, chunk_by_tokens

chunks = chunk_text(document, chunk_size=1000, overlap=100)
# overlapping chunks so answers aren't split across a boundary

# Budget by tokens instead of characters (exact with tiktoken installed):
chunks = chunk_by_tokens(document, chunk_size=500, overlap=50)

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API reference

Function	Description
count_tokens(text, model=None)	Exact (tiktoken) or estimated token count
estimate_tokens(text)	Dependency-free heuristic count
truncate_to_tokens(text, max_tokens, model=None)	Trim text to a token budget
estimate_cost(input_tokens, output_tokens, model, pricing=None)	USD cost estimate
retry(attempts, base_delay, backoff, jitter, exceptions, ...)	Backoff retry decorator (sync and async)
PromptTemplate(template)	Templating with missing-variable validation
chunk_text(text, chunk_size, overlap)	Overlapping text chunks (by character)
chunk_by_tokens(text, chunk_size, overlap, model=None)	Overlapping text chunks (by token budget)
extract_json(text, default=...)	Parse the first JSON value out of an LLM reply

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Development

git clone https://github.com/YoungAlpaccino/llmbelt
cd llmbelt
pip install -e ".[dev]"
pytest          # run tests
ruff check .    # lint

Publishing to PyPI (maintainer notes)

python -m build
twine upload dist/*

Before first publish: confirm the name llmbelt is free on PyPI. If taken, rename in pyproject.toml, the src/ folder, and imports (a single find-and-replace).

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License

MIT — see LICENSE. Use it anywhere, including commercially.