---
title: "ACP: the Atomic Content Protocol"
url: https://stacklist.com/card/70ff5d46-8612-4292-9f4d-5f3b9fb06a62
source_url: "https://stacklist.com/acp"
stack: https://stacklist.com/stack/c252b545-15f1-411c-bb29-d4d420615f73
summary: "Atomic Content Protocol (ACP) is a standardized format for structuring content with YAML frontmatter that carries identity, provenance, and relationships, reducing token consumption by 98% through enriched metadata. ACP v0.2 ships as a production-ready open standard readable by any LLM, MCP server, or text editor, solving the format problem that MCP left unsolved."
tags: "atomic-content-protocol, knowledge-representation, mcp, token-economy, semantic-metadata"
key_entities: "John McCarthy (person), Atomic Content Protocol (technology), Model Context Protocol (technology), Knowledge representation and reasoning (concept), Semantic network (concept), Stacklist (organization)"
classification: "reference"
content_hash: "sha256:050b2ee7dc190567143b24b0f974b32fe41bff1cd6a603a5232a15811f9d6041"
acp_version: "0.2"
token_counts_approximate: 1307
visibility: public
agent_accessible: true
status: "final"
---

# ACP: the Atomic Content Protocol

Atomic Content Protocol MCP is the pipe. ACP is the payload. MCP standardised how agents connect to data. ACP standardises what the data looks like when it arrives: Markdown with YAML frontmatter that carries its own identity, provenance, and relationships. Read the spec See an ACO Open standard. Readable by any LLM, any MCP server, any text editor. --- id : 01a03d62-f05a-7639-a015-be6d5d18218a acp_version : "0.2" object_type : aco source_type : link source_url : https://en.wikipedia.org/wiki/Knowledge_... created : 2026-08-26T09:24:49Z content_hash : sha256:c8dc3f6156b9a0bbf70a2ea468635356... language : en classification : reference token_counts : cl100k : 9357 approximate : 11643 tags : [knowledge-representation, ontologies, reasoning] key_entities : - {type: person, name: John McCarthy, confidence: 0.95} - {type: concept, name: Semantic network, confidence: 0.90} summary : > Knowledge representation and reasoning is a field of artificial intelligence focused on modelling information in structured formalisms so that computer systems can solve complex tasks. provenance : summary : {model: claude-opus-4-6, confidence: 0.85} visibility : private agent_accessible : true --- # Knowledge representation and reasoning Knowledge representation and reasoning (KRR) is the field of artificial intelligence dedicated to representing information... A real ACO, returned by the Stacklist MCP server today. Not a mockup. the problem An agent can reach your content. It still has to read all of it. MCP solved the connection. It did not change what arrives at the other end: a wall of text with no identity, no history, and no idea what it relates to. Every read pays full price, and every agent has to work it out again from scratch. Full cost, every read 11,643 tokens. Then 11,643 again. No provenance Who made it, when, how sure. No relationships What it supersedes or contradicts. No access rules Private, public, agent-readable. None of this is a model problem. It is a format problem. the object What an ACO carries. Six required fields. Everything else optional. An ACO is a valid .md file that any text editor, static site generator, or LLM reads without special tooling. Identity id · acp_version · object_type A UUID, the spec version, and what kind of object this is. Provenance source_type · source_url · author · created Where it came from, who made it, and when. Integrity content_hash SHA-256 of the body. Change the content, change the hash. Economy token_counts Per-tokeniser counts, so an agent can budget before it reads. Classification tags · classification · key_entities · language Machine-generated at enrichment, each entity confidence-scored. Field provenance provenance.<field> Per field: which model produced it, when, and how confident. Access visibility · agent_accessible · status Who may read it, and whether agents are among them. relationships[] — typed, directional edges (references, derived-from, supersedes, contradicts) — is specified in the schema and not yet populated in production. the token economy 11,643 tokens become 200. Enrichment writes a summary, tags, entities and counts into the frontmatter once. After that an agent can decide whether to read the body at all — and usually does not need to. Measured, not modelled: these are the figures the Stacklist MCP server returned for one Wikipedia article. Raw page 11,643 tokens As an ACO ~200 tokens 98% fewer tokens per read Break-even after one read. Every read after that is profit. what is real ACP v0.2 ships today. Every capsule created in Stacklist is a real ACO, enriched at write time and readable over MCP. The protocol is not waiting on a launch: it is what the product already stores. Source types, all live link manual selected_text llm_capture uploaded_md converted_pdf converted_doc converted_video uploaded_image MCP tools that read and write ACOs enrich capsule save_markdown save_llm_output get_card_content search_semantic_similar Verified against @stacklist/mcp-server 2.0.0 on 26 August 2026. The ACO in the hero came back from a live enrich call, not a design file. the standard Four primitives. Two levels. No more. A tiny mandatory core keeps the spec implementable and the edge cases few. Containers do not nest. Collections do not recurse. That constraint is deliberate and can be relaxed later. ACO The unit. Markdown plus YAML frontmatter: self-describing, addressable, portable. live today Container An ordered, addressable group of ACOs with its own metadata and access rules. specified Collection A group of Containers with rollup counts. The second and final level. specified Owner The identity anchor. The root of a knowledge graph, public or private. specified Core relationship edges references derived-from supersedes supports contradicts part-of related x- extensions Closed core set, extensible with an x- prefix. The edge vocabulary is specified and not yet populated in production. A public ACO registry — enrich once, everyone benefits — is the phase after that. Read the spec. Then read an object. ACP is an open standard. Stacklist is the first network built on it. Read the spec Connect the MCP server Markdown in, Markdown out. Your objects are portable by construction.