ATOMIC CONTENT PROTOCOL
What is an ACO?
An Atomic Content Object is the smallest piece of knowledge that still explains itself. Markdown you can read, frontmatter a machine can trust.
Key facts
- SPEC VERSION
- ACP v0.2
- FORMAT
- Markdown + YAML
- REQUIRED FIELDS
- Six
- LIVE IN
- Stacklist MCP 2.0
THE IDEA
Content that arrives already understood.
A file tells you almost nothing. It has a name, a size, and a body. Everything else — what it is about, where it came from, whether it is still true, who may read it — lives in someone's head or in a database the agent cannot see.
An ACO puts that knowledge in the object itself. The frontmatter is not decoration: it is the part a machine reads first, and often the only part it needs.
The six required fields
- id
- uuidStable across exports, forks, and implementations.
- acp_version
- stringWhich version of the spec this object conforms to.
- object_type
- "aco"Distinguishes an object from a container or collection.
- source_type
- enumlink · manual · llm_capture · uploaded_md · converted_pdf …
- created
- ISO 8601UTC, always. modified is optional and separate.
- author
- objectid and name. Survives in provenance when content is forked.
Questions
Is ACP the same as MCP?
No. MCP is transport: how an agent connects to a source. ACP is content: what arrives when it does. Use either without the other; together they close the loop.
Do I need Stacklist to use ACP?
No. An ACO is a Markdown file. Stacklist is the first network built on the protocol, not a requirement of it.
What makes it "atomic"?
Indivisible at its level of abstraction. An ACO is the smallest unit that is still independently meaningful, addressable, and portable.
Where does the metadata come from?
Enrichment generates it at write time. Each field is confidence-scored and carries provenance recording which model produced it and when.
Can I export my objects?
They are already exported. The canonical form is a .md file — drop one into an Obsidian vault and it renders.
What is not built yet?
Containers and Collections are specified but are not yet ACP objects in production. Typed relationship edges are defined and not yet populated. A public ACO registry comes after both.
Spec updates.
v0.2 is current. We will email you when the next version lands, and when the registry opens.
Spec traffic only. No product mail.