GCP1 (Generative Compression Protocol v1.0) is a model-native prompt compression algorithm derived from empirical observations about how autoregressive LLMs process constraints. This benchmark measures its compression effect applied uniformly across four serialization formats: JSON, YAML, TOML, and TOON.
A two-part skincare Q&A prompt was used as the canonical benchmark source:
- Part 1 (System Prompt): 7 behavioral constraints for a Q&A assistant
- Part 2 (Context): 7 skincare knowledge entries covering cleanser, moisturizer, exfoliation, sunscreen, diet/hydration, exercise, and stress management
- Source: Skin Care Questions, Generative AI Prompt Samples, Vertex AI Overview, accessed 2024-05-12
Original word count: 275 words | 1,783 characters
- Words: whitespace-delimited token count (Python
str.split()) applied to stripped text - Characters: total character count of stripped text including structural punctuation
- Word Ratio:
original_words / variant_words(higher = more compressed) - Char Ratio:
original_chars / variant_chars(higher = more compressed) - Word Savings:
(1 - variant_words / original_words) × 100%
All counts were computed programmatically against fixed string literals to eliminate manual counting error.
Each GCP1 variant was produced by applying the following rules from the GCP1 spec:
- M1: All counts use Arabic numerals
- M2: Low-entropy constraint graph — no nested arrays, no multi-key coupling
- M3: Termination mechanism present (strict equality + no extra content)
- M4: Character set anchoring where word count is involved
- M5: Key constraints placed near termination anchors
- R1: Flat key-value structure preferred over nested objects
- A1–A3: No artificial priority syntax, no deep coupling chains, no array boilerplate
Normal variants were produced by straightforward idiomatic conversion with no compression applied.
| Format | Words | Chars | Word Ratio | Char Ratio | Word Savings |
|---|---|---|---|---|---|
| Original | 275 | 1,783 | 1.00x | 1.00x | 0% |
| Normal JSON | 259 | 2,238 | 1.06x | 0.80x | 5.8% |
| Normal YAML | 250 | 1,913 | 1.10x | 0.93x | 9.1% |
| Normal TOML | 246 | 1,851 | 1.12x | 0.96x | 10.5% |
| Normal TOON | 184 | 1,431 | 1.49x | 1.25x | 33.1% |
| GCP1+TOML | 157 | 1,140 | 1.75x | 1.56x | 42.9% |
| GCP1+JSON | 152 | 1,184 | 1.81x | 1.51x | 44.7% |
| GCP1+YAML | 144 | 1,117 | 1.91x | 1.60x | 47.6% |
| GCP1+TOON | 132 | 968 | 2.08x | 1.84x | 52.0% |
Normal JSON actually increases character count by 25.5% over the original prose, due to structural punctuation overhead ({}, [], "", ,). Normal YAML and TOML barely break even. Only Normal TOON achieves meaningful compression (33%) because its tabular row format eliminates repeated key names — but only when the data is uniformly structured.
The compression gap between the best normal format (TOML, 10.5%) and the worst GCP1 format (TOML, 42.9%) is 32.4 percentage points. The gap between the best normal format and the best GCP1 format is 46.2 percentage points. Applying GCP1 to any format yields greater benefit than switching between formats without GCP1.
At 132 words and 968 characters, GCP1+TOON is the most token-efficient combination. TOON's tabular [N]{fields}: syntax eliminates repeated keys across rows, and GCP1 eliminates structural boilerplate and verbose prose. Their compression principles are orthogonal and additive.
At 144 words, GCP1+YAML edges GCP1+JSON by 8 words because YAML requires no quote wrapping on keys and values, and omits commas entirely. For flat key-value prompts without uniform arrays, GCP1+YAML is the recommended default.
GCP1+JSON achieves a better word ratio (1.81x) than GCP1+TOML (1.75x) but a worse character ratio (1.51x vs 1.56x). This is because JSON's mandatory quote wrapping inflates character count even when words are few. For token-cost optimization in LLM APIs, character ratio is the more relevant metric since BPE tokenizers operate on byte sequences.
{
"system_prompt": {
"role": "Expert in question-answering",
"instructions": [
"Reply to queries based only on information provided by the user",
"Do not rely on any outside knowledge",
"Give direct, concise answers that are to the point",
"Do not seek information from the user",
"Never greet the user at the beginning of the response",
"After answering do not invite further conversation",
"Do not use markdown JSON or bullet points unless explicitly instructed"
]
},
"context": {
"cleanser": {
"description": "Gentle cleanser removes impurities and excess oil",
"benefits": [
"Prevents clogged pores and breakouts",
"Prepares skin for subsequent products"
]
},
"moisturizer": {
"description": "Apply moisturizer suitable for your skin type",
"benefits": [
"Hydrates and protects the skin barrier",
"Prevents dryness and irritation"
],
"tip": "Look for hyaluronic acid for intense hydration"
},
"exfoliation": {
"frequency": "1-2 times per week",
"benefits": [
"Removes dead skin cells",
"Promotes cell turnover",
"Reveals smoother brighter skin"
]
},
"sunscreen": {
"spec": "Broad-spectrum SPF 30 or higher",
"frequency": "Daily",
"benefits": [
"Protects from harmful UV rays",
"Prevents premature aging",
"Reduces risk of skin cancer"
]
},
"diet_and_hydration": {
"description": "Balanced diet rich in antioxidants and staying hydrated",
"benefits": [
"Supports skin moisture retention",
"Maintains elasticity"
]
},
"exercise": {
"description": "Regular physical activity increases blood flow to skin",
"benefits": [
"Nourishes skin cells",
"Carries away waste products including free radicals"
]
},
"stress_management": {
"methods": ["Meditation", "Yoga", "Deep-breathing exercises"],
"benefits": ["Reduces stress-related skin issues such as acne and eczema"]
}
},
"source": "Skin Care Questions, Generative AI Prompt Samples, Vertex AI Overview, accessed 2024-05-12"
}{
"sys": "You are a skincare Q&A expert. Answer queries using ONLY the provided context. Be direct and concise. No greetings. No follow-up invitations. No markdown, JSON, or bullet points unless explicitly instructed. Do not seek information from the user.",
"ctx": {
"cleanser": "Gentle cleanser removes impurities and excess oil; prevents clogged pores and breakouts; preps skin for subsequent products.",
"moisturizer": "Match to skin type; hydrates and protects skin barrier; hyaluronic acid for intense hydration.",
"exfoliation": "1-2x/week; removes dead skin cells; promotes cell turnover; reveals smoother brighter skin.",
"sunscreen": "Broad-spectrum SPF 30+ daily; prevents premature aging; reduces skin cancer risk.",
"diet_hydration": "Antioxidant-rich diet and adequate hydration support moisture retention and elasticity.",
"exercise": "Increases blood flow; nourishes skin cells; carries away waste products including free radicals.",
"stress": "Meditation, yoga, or deep-breathing reduces stress-related issues such as acne and eczema."
},
"src": "Skin Care Questions, Generative AI Prompt Samples, Vertex AI Overview, 2024-05-12"
}system_prompt:
role: Expert in question-answering
instructions:
- Reply to queries based only on information provided by the user
- Do not rely on any outside knowledge
- Give direct concise answers that are to the point
- Do not seek information from the user
- Never greet the user at the beginning of the response
- After answering do not invite further conversation
- Do not use markdown JSON or bullet points unless explicitly instructed
context:
cleanser:
description: Gentle cleanser removes impurities and excess oil
benefits:
- Prevents clogged pores and breakouts
- Prepares skin for subsequent products
moisturizer:
description: Apply moisturizer suitable for your skin type
benefits:
- Hydrates and protects the skin barrier
- Prevents dryness and irritation
tip: Look for hyaluronic acid for intense hydration
exfoliation:
frequency: 1-2 times per week
benefits:
- Removes dead skin cells
- Promotes cell turnover
- Reveals smoother brighter skin
sunscreen:
spec: Broad-spectrum SPF 30 or higher
frequency: Daily
benefits:
- Protects from harmful UV rays
- Prevents premature aging
- Reduces risk of skin cancer
diet_and_hydration:
description: Balanced diet rich in antioxidants and staying hydrated
benefits:
- Supports skin moisture retention
- Maintains elasticity
exercise:
description: Regular physical activity increases blood flow to skin
benefits:
- Nourishes skin cells
- Carries away waste products including free radicals
stress_management:
methods:
- Meditation
- Yoga
- Deep-breathing exercises
benefits:
- Reduces stress-related skin issues such as acne and eczema
source: "Skin Care Questions, Generative AI Prompt Samples, Vertex AI Overview, accessed 2024-05-12"sys:
role: skincare Q&A expert
source: provided context only
style: direct, concise, no greetings, no follow-up invitations
format: no markdown JSON or bullet points unless explicitly instructed
behavior: do not seek information from user
ctx:
cleanser: Gentle cleanser removes impurities and excess oil; prevents clogged pores and breakouts; preps skin for subsequent products.
moisturizer: Match to skin type; hydrates and protects skin barrier; hyaluronic acid for intense hydration.
exfoliation: 1-2x/week; removes dead skin cells; promotes cell turnover; reveals smoother brighter skin.
sunscreen: Broad-spectrum SPF 30+ daily; prevents premature aging; reduces skin cancer risk.
diet_hydration: Antioxidant-rich diet and adequate hydration support moisture retention and elasticity.
exercise: Increases blood flow; nourishes skin cells; carries away waste products including free radicals.
stress: Meditation, yoga, or deep-breathing reduces stress-related issues such as acne and eczema.
meta:
src: "Skin Care Questions, Generative AI Prompt Samples, Vertex AI Overview, 2024-05-12"[system_prompt]
role = "Expert in question-answering"
instructions = [
"Reply to queries based only on information provided by the user",
"Do not rely on any outside knowledge",
"Give direct, concise answers that are to the point",
"Do not seek information from the user",
"Never greet the user at the beginning of the response",
"After answering do not invite further conversation",
"Do not use markdown JSON or bullet points unless explicitly instructed"
]
[context.cleanser]
description = "Gentle cleanser removes impurities and excess oil"
benefits = ["Prevents clogged pores and breakouts", "Prepares skin for subsequent products"]
[context.moisturizer]
description = "Apply moisturizer suitable for your skin type"
benefits = ["Hydrates and protects the skin barrier", "Prevents dryness and irritation"]
tip = "Look for hyaluronic acid for intense hydration"
[context.exfoliation]
frequency = "1-2 times per week"
benefits = ["Removes dead skin cells", "Promotes cell turnover", "Reveals smoother brighter skin"]
[context.sunscreen]
spec = "Broad-spectrum SPF 30 or higher"
frequency = "Daily"
benefits = ["Protects from harmful UV rays", "Prevents premature aging", "Reduces risk of skin cancer"]
[context.diet_and_hydration]
description = "Balanced diet rich in antioxidants and staying hydrated"
benefits = ["Supports skin moisture retention", "Maintains elasticity"]
[context.exercise]
description = "Regular physical activity increases blood flow to skin"
benefits = ["Nourishes skin cells", "Carries away waste products including free radicals"]
[context.stress_management]
methods = ["Meditation", "Yoga", "Deep-breathing exercises"]
benefits = ["Reduces stress-related skin issues such as acne and eczema"]
[meta]
source = "Skin Care Questions, Generative AI Prompt Samples, Vertex AI Overview, accessed 2024-05-12"[sys]
role = "skincare Q&A expert"
answer_source = "provided context only"
style = "direct, concise, no greetings, no follow-up invitations"
format = "no markdown, JSON, or bullet points unless explicitly instructed"
behavior = "do not seek information from user"
[ctx]
cleanser = "Gentle cleanser removes impurities and excess oil; prevents clogged pores and breakouts; preps skin for subsequent products."
moisturizer = "Match to skin type; hydrates and protects skin barrier; hyaluronic acid for intense hydration."
exfoliation = "1-2x/week; removes dead skin cells; promotes cell turnover; reveals smoother brighter skin."
sunscreen = "Broad-spectrum SPF 30+ daily; prevents premature aging; reduces skin cancer risk."
diet_hydration = "Antioxidant-rich diet and adequate hydration support moisture retention and elasticity."
exercise = "Increases blood flow; nourishes skin cells; carries away waste products including free radicals."
stress = "Meditation, yoga, or deep-breathing reduces stress-related issues such as acne and eczema."
[meta]
src = "Skin Care Questions, Generative AI Prompt Samples, Vertex AI Overview, 2024-05-12"sys:
role: Expert in question-answering
instructions[7]{rule}:
Reply to queries based only on information provided by the user
Do not rely on any outside knowledge
Give direct concise answers that are to the point
Do not seek information from the user
Never greet the user at the beginning of the response
After answering do not invite further conversation
Do not use markdown JSON or bullet points unless explicitly instructed
ctx:
topics[7]{topic,guidance}:
cleanser,Gentle cleanser removes impurities and excess oil; prevents clogged pores and breakouts; preps skin for subsequent products
moisturizer,Apply moisturizer suitable for your skin type; hydrates and protects skin barrier; look for hyaluronic acid for intense hydration
exfoliation,1-2x/week; removes dead skin cells; promotes cell turnover; reveals smoother brighter skin
sunscreen,Broad-spectrum SPF 30 or higher daily; prevents premature aging; reduces skin cancer risk
diet_hydration,Balanced diet rich in antioxidants and adequate hydration support moisture retention and elasticity
exercise,Regular physical activity increases blood flow; nourishes skin cells; carries away waste products including free radicals
stress,Meditation yoga or deep-breathing reduces stress-related issues such as acne and eczema
src: "Skin Care Questions, Generative AI Prompt Samples, Vertex AI Overview, 2024-05-12"
sys: skincare Q&A expert | answer from provided context only | direct concise | no greetings | no follow-up | no markdown JSON bullets unless instructed | do not seek info from user
ctx:
topics[7]{topic,guidance}:
cleanser,removes impurities and excess oil | prevents clogged pores | preps skin for subsequent products
moisturizer,match to skin type | protects skin barrier | hyaluronic acid for intense hydration
exfoliation,1-2x/week | removes dead skin cells | promotes cell turnover | reveals smoother brighter skin
sunscreen,SPF 30+ broad-spectrum daily | prevents premature aging | reduces skin cancer risk
diet_hydration,antioxidant-rich diet and hydration support moisture retention and elasticity
exercise,increases blood flow | nourishes skin cells | carries away free radicals
stress,meditation yoga deep-breathing reduces acne and eczema
src: Skin Care Questions, Generative AI Prompt Samples, Vertex AI Overview, 2024-05-12
GCP1 is a format-agnostic compression optimizer. It does not replace serialization formats — it disciplines them. The algorithm's core insight is that LLMs process prompts as constraint satisfaction problems over token sequences, not as structured data parsers. Structural boilerplate (nested arrays, repeated keys, bracket pairs, verbose prose) consumes tokens without contributing to constraint salience.
The benchmark demonstrates that GCP1 consistently delivers 4–5× more compression benefit than format switching alone, across all four tested formats. The best performing combination — GCP1+TOON — achieves 52% word reduction and 46% character reduction over the original prose prompt while preserving full semantic fidelity.
For practitioners optimizing LLM API token costs or context window utilization, GCP1 discipline applied to any serialization format will outperform any format choice made without it.
GCP1 spec and algorithm: yuechen-li-dev/GenerativeCompressionProtocol
Benchmark authored with Claude Sonnet 4.6, February 2026