PromptMin

Minify LLM prompts to save tokens — without losing meaning.

LLM APIs charge per token, and non-English prompts (especially Spanish) can use 20–30% more tokens than their English equivalents. PromptMin rewrites your prompts into a denser form using curated, domain-aware substitutions, and reports real token savings measured with tiktoken.

Core guarantee. Every substitution rule is validated against tiktoken at runtime. If a rule does not reduce token count, it is skipped. PromptMin never makes your prompt longer.

Why?

Most "token savers" are naive find-and-replace scripts that don't actually save tokens (because BPE tokenizers don't count characters). PromptMin is different:

• Mathematically validated. Rules are only applied when the tokenizer confirms they save tokens.
• Curated, not massive. ~400 high-signal rules beat 100,000 random ones.
• Domain-aware. Activate dictionaries by context (web, backend, ai…) for aggressive but safe compression.
• Multi-tokenizer. Optimize for the model you target: GPT-4o, GPT-4, Claude, Gemini.
• Bilingual. First-class Spanish + English, extensible to any language via YAML.
• Honest benchmarks. Run promptmin benchmark on your own corpus and see real numbers.

Real numbers

Measured on the included corpus examples/corpus_domains.txt (18 mixed EN/ES technical prompts):

Savings by configuration (tokenizer: gpt-4):

Savings by tokenizer (config: lite + all domains):

The newer gpt-4o tokenizer (o200k_base) is already more efficient on raw text than cl100k_base, which is why PromptMin has slightly less margin to optimize on it. This is the honest reality — and exactly why benchmarking matters.

Zero regressions across all modes and all tokenizers. The validator guarantees it.

A note on Spanish prompts and modern tokenizers

If you write prompts in Spanish and target gpt-4o (or any modern o200k_base-family model), always use --translate. Without it, savings are modest (~10-15%). With it, savings jump to ~25-40%.

Why? Modern BPE tokenizers learn very efficient merges for common Spanish constructs like "una función", "la base de datos", "por favor". Substituting a single word ("función" → "func") inside Spanish text often produces zero token savings because the original Spanish merge was already compact. The only reliable way to save tokens on Spanish is to rewrite larger chunks into English at once, so BPE merges align on both sides.

This is why PromptMin v0.3+ uses phrase-level translation patterns (dicts/es_en_phrases.yaml) as the primary strategy for Spanish, applied BEFORE word-level rules. A simple prompt like:

"Por favor, desarrolla una función en Python que consulte la base de datos de usuarios y retorne un JSON con los activos"

goes from 24 → 15 tokens (37.5% saved) on gpt-4o with --translate, vs only 12.5% without.

Install

pip install promptminify

On PyPI the package is promptminify (because promptmin was already taken), but the CLI command and Python import name are both promptmin:

promptmin --help

from promptmin import minify

From source (development)

git clone https://github.com/DelvyG/promptmin.git
cd promptmin
pip install -e ".[dev]"

Usage

CLI

# Inline
promptmin run "Please, I would like you to build a function step by step"

# From file / clipboard / stdin
promptmin run --file prompt.txt
promptmin run --clipboard --out-clipboard
cat prompt.txt | promptmin run

# With domain dictionaries
promptmin run -d web,backend "Improve the user experience and add JWT authentication"

# Target a specific model's tokenizer
promptmin run -T claude "..."
promptmin run -T gpt-4o "..."
promptmin run -T gemini "..."

# List all available tokenizers
promptmin tokenizers

# Spanish with automatic EN technical translation
promptmin run -t "Por favor, desarrolla una función paso a paso para la base de datos"

# Aggressive mode (strips more filler)
promptmin run -m aggressive "..."

# List available domain dictionaries
promptmin domains

# Benchmark on a corpus
promptmin benchmark examples/corpus_domains.txt -d web,backend,devops,data,ai

# Just count tokens
promptmin count "hello world"

As a library

from promptmin import minify
from promptmin.tokens import savings

result = minify(
    "Please improve the user experience on mobile responsive devices",
    domains=["web"],
)
print(result["minified"])
print(savings(result["original"], result["minified"]))
# {'before': 11, 'after': 7, 'saved': 4, 'pct': 36.4}

How it works

┌─────────────┐
│  Your text  │
└──────┬──────┘
       ▼
┌─────────────────────┐
│ 1. Detect language  │  es / en (cheap heuristic)
└──────┬──────────────┘
       ▼
┌─────────────────────────────────────┐
│ 2. Domain dicts (highest priority)  │  e.g. "user experience" -> "UX"
└──────┬──────────────────────────────┘
       ▼
┌─────────────────────────┐
│ 3. Language dict        │  "please" -> "", "configuration" -> "config"
└──────┬──────────────────┘
       ▼
┌───────────────────────────────────┐
│ 4. ES→EN translation (optional)   │  "desarrolla" -> "build"
└──────┬────────────────────────────┘
       ▼
┌─────────────────────┐
│ 5. Stopword strip   │
└──────┬──────────────┘
       ▼
┌─────────────────────┐
│ 6. Whitespace clean │
└──────┬──────────────┘
       ▼
┌──────────────────────────────┐
│  Minified output + stats     │
└──────────────────────────────┘

The validator. Every step applies rules one at a time. Before accepting a substitution, it calls tiktoken.encode() on before/after. If tokens didn't drop, the rule is discarded. This is why PromptMin can't make your prompt worse.

Dictionary architecture

src/promptmin/dicts/
├── en.yaml              General English rules
├── es.yaml              General Spanish rules
├── es_en.yaml           Spanish → English technical translation
└── domains/
    ├── ai.yaml          LLM / RAG / CoT / fine-tuning / embeddings
    ├── backend.yaml     API / JWT / ORM / middleware / queues
    ├── data.yaml        ETL / warehouses / KPIs / schemas
    ├── devops.yaml      CI/CD / Kubernetes / SLO / observability
    └── web.yaml         UX / UI / SPA / PWA / responsive

Each file is plain YAML: "long phrase": "short version". No code required to contribute a new domain — drop a YAML file in dicts/domains/ and it's automatically picked up by promptmin domains.

Roadmap

• Phase 1 — MVP CLI (EN + ES dicts, tiktoken-validated)
• Phase 2 — Benchmark on real corpus, lite / aggressive / translate modes
• Phase 2.5 — Domain dictionaries (web, backend, devops, data, ai)
• Phase 3 — Multi-tokenizer support: GPT-4o / GPT-4 / Claude / Gemini
• Phase 3.5 — Spanish phrase-level translation (es_en_phrases.yaml)
• Phase 3.6 — Official SDK integration for exact Claude/Gemini counts (optional extras)
• Phase 3.6 — More phrase patterns based on real-usage corpora
• Phase 4 — VSCode extension ("Minify Selection" + keybinding)
• Phase 4 — More domains: mobile, security, gamedev, finance
• Phase 4 — Domain auto-detection from prompt content

Contributing

Contributions are very welcome — especially new domain dictionaries and language support. See CONTRIBUTING.md.

The lowest-friction contribution is a new domain YAML: no Python, no tests, just curated phrases.

License

MIT © DelvyG