Deterministic serialization for multi-agent LLM sessions - 3.45x fewer tokens than JSON, up to 9.9x for non-English content

Multi-agent LLM systems -” several models exchanging messages within

one session -” pay for context, not intelligence. Every round trip in

natural language or verbose JSON burns tokens re-stating structured

context that a fixed, external schema could carry in a fraction of

the size.

I got tired of watching this happen in my own pipelines, so I built a

small serialization protocol to fix it. Sharing it here in case it's

useful to others hitting the same wall.

Move inter-agent messages from natural language / JSON to short,

positional ASCII identifiers (P1:A2:X0:V4

), resolved against an

external, versioned dictionary.json

. A deterministic Python layer

handles encode/decode -” no model involved in reconstructing meaning,

so there's no hallucination risk on the decode side.

def encode(payload: dict, schema: dict) -> str:
    parts = []
    for field_name, field_id in schema["fields"].items():
        if field_name not in payload:
            continue
        value = str(payload[field_name])
        value_id = schema["values"][field_name][value]
        parts.append(f"{field_id}{value_id}")
    return ":".join(parts)

Unknown fields or values raise an explicit error instead of guessing -”

the whole point of an external schema is that the model never has to

improvise meaning on decode.

Conceptually this is closer to Protocol Buffers than to prompt

engineering: a fixed contract, not a clever prompt.

Measured on cl100k_base

(industry-standard reference tokenizer):

3.45x fewer tokens than JSON. Full reproducible benchmark script

is in the repo -” run it yourself against your own tokenizer before

trusting these numbers for a cost projection.

Tokenizer vocabularies are trained predominantly on English text, so

non-Latin scripts pay a real, measurable tax. Same sentence, same

meaning, measured multiplier vs. the SCP ID-stack:

Because the ID-stack costs the same regardless of source language (9

tokens either way -” it's just ASCII after encoding), SCP's savings

scale disproportionately for non-English multi-agent deployments.

That's not a marketing angle, it's just what the tokenizer does.

cl100k_base

as a common reference point. If you're deploying against a different model family, re-run the benchmark script against that tokenizer before relying on these numbers.Anthropic and OpenAI both offer ~90% discounts on cached input tokens.

Three conditions determine whether SCP's savings actually materialize

in a caching setup:

python mvp/encoder_decoder.py encode '{"system": "Quantumoan", "version": "4", "action": "paradigm_shift", "target": "cognitive_profiles_alignment"}'

python mvp/encoder_decoder.py decode "P1:V4:A2:X0"

Repo (AGPLv3): https://github.com/andrey-architect/scp-protocol

Would genuinely like to know where this breaks -” issues and PRs welcome.