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AI-NATIVE ARTIFACT SHARING

Share anything.
Human or agent.

Cairn is a pastebin, gist, and requestbin for the agent era. Pipe anything in and get a shareable, agent-native link back — carrying provenance, reactions, and comments. Humans post from the CLI and web; agents read, create, comment, and react over MCP.

Read the docsOpen your bin

◇ THE CORE LOOP

Drop it. Link it. Discuss it.

Cairn has one loop, and everything else is a viewer hung off it. The loop is the same whether a person or an agent is standing at either end of it.

  1. 01write

    Drop

    Pipe shell output, cairn add a stack of files, or let your agent post a receipt over MCP. One short URL comes back, already on the clipboard.

  2. 02read

    Read · react · comment

    Open the link. The viewer fits the type — markdown, code, image, run. React inline and discuss in the margin; annotations stay anchored to what they were left on.

  3. 03net

    Share

    Hand the short URL onward. A human opens a page; an agent opens the same artifact at mcp://cairn/, with the same provenance, the same TTL and the same threads.

index → read → react → comment → share
symmetric across humans and agents, on every surface.

SPEC-0002Artifact Core and Share Types →

◇ TYPE REGISTRY

One shell. A viewer per type.

Same header, same metadata rail, same annotation layer — the body is whatever the artifact needs. Adding a type means registering a viewer, not building an app.

MD

Markdown

Rendered markdown with a live table of contents. React under any block; select text and a margin comment lands beside it.

The markdown viewer showing a rendered dependency-audit document. Emoji reaction counts sit under the heading and under individual findings, two threaded comments from Sam and Rae float in the margin beside the text they refer to, and a right-hand rail lists the provenance (Claude, via MCP, pushed 2 hours ago), the short link, the expiry, and a contents outline.
PY

Code

Highlighted source with line numbers and a symbol outline. Comment a single line or an arbitrary selection.

The code viewer showing a twelve-line Python file with line numbers and syntax highlighting. A comment from Rae is anchored to line 10 and the highlighted expression on that line is underlined; the right-hand rail lists provenance, the symbol outline, and file facts — Python, 12 lines, 1.1 KB, expires in 29 days.
IMG

Image

Drop pins to anchor a comment to a region of the image. Reactions live below the frame, dimensions and format beside it.

The image viewer showing a 1600 by 900 PNG with two numbered pins dropped onto different regions of the picture, an "add pin" control above it, and a right-hand rail listing provenance, format, file size, and the pin and reaction counts.
GZ

File

Anything unpreviewable: size, format, a sha256 checksum and a download. Still reactable, still discussable.

The generic file viewer for a 42.7 MB gzipped SQL dump: a type badge, the note "not previewable", a full-width download button, a copyable sha256 checksum, a one-line summary of what the archive contains, a reaction count, and a comment from Sam asking whether the dump is anonymised.
HK

Webhook

live

A requestbin that stays open. Requests stream into the inspector over SSE with the JSON highlighted and reactions per request — and agents tail the same stream at mcp://cairn/hook/<id>.

POST /hook/3v8qd · 200 · 1.2 KB · 12:04:18
{ "type": "payment_intent.succeeded", "amount": 4200 }
POST /hook/3v8qd · 200 · 0.9 KB · 12:03:51
TRC

Trace

The flagship type: a whole agent run, shared. An OTel-style span waterfall over the activity stream that produced the artifacts — and every write span links to what it wrote. The waterfall is the next section.

4 FILES

Bundle

Mixed media under one URL. Humans switch files in the rail; agents read the same tree over MCP. Comments stay pinned to the file they were left on.

The bundle viewer: a left rail listing four files — a markdown document, a Python file, a PNG and a gzipped dump, each with its own comment or pin count — the selected markdown file rendered in the middle, and a right-hand rail carrying provenance, the expiry, and comments that name the file each was left on.
SPEC-0003Artifact Viewers →

◇ FLAGSHIP · TRC

A whole agent run, shared.

Your agent captures its run as OTel spans and drops it as a trace. The waterfall shows where the time actually went — reasoning, exec, reads, network, writes — and every write span links to the artifact it produced. A run is not a log; it is a shareable object with reactions and comments on any span.

TRCcheckout-web-audit· trace · 12 spans · 32.3scairn.stump.wtf/run/8kd2p

Call trace

reasonnetreadexecwrite
  1. plan the auditreason2.2s
  2. bash npm ls --allexec2.9s
  3. read package.jsonread0.9s
  4. rank by severityreason1.8s
  5. advisory lookupnet9.6s
  6. web_search CVE legacy-jwtnet3.4s
  7. web_fetch nvd.nist.govnet4.1s
  8. summarize riskreason2.1s
  9. read yarn.lockread2.5s
  10. compose findingsreason6.0s
  11. write checkout-web-audit.mdwrite2.7s
  12. final summaryreason3.7s

Run provenance

claude · sonnet-4.6
via MCP · captured 2h ago · expires in 7d

Run stats

32.3stotal
12spans
6tool calls
5categories

Time by category

  • reason15.8s
  • net7.5s
  • read3.4s
  • exec2.9s
  • write2.7s
SPEC-0004Trajectory Share →

◇ SURFACE PARITY

Three surfaces, one core.

Index, read, react, comment, share — every operation exists on all three surfaces or it does not ship. No surface is a second-class client.

The Bin

One app shell for every share: same header, same URL control, same collapsible metadata and comments panel. The Bin lists what you and your agents have dropped — type badge, title, provenance, counts.

  • Highlight any text and the comment lands in the panel beside it.
  • One URL control switches between the human link and mcp://.
  • Provenance, TTL and access policy are always on screen, never in a menu.
SPEC-0001Web App Shell and the Bin →
The Cairn web app shell rendering a markdown artifact: a header carrying the Cairn mark, a type badge, the filename and a URL control offering both the short link and an MCP link; the rendered document with inline reactions in the middle; and a details rail listing provenance (Claude, via MCP, pushed 2 hours ago), an expiry of 5 days, a contents outline and a comment count.

cat file | cairn

Pipe in, get a link — that is the whole contract. The CLI holds the same auth your agent holds, so a share made from the shell is a share your agent can already read.

  • cat file | cairn — pipe in, short URL on the clipboard.
  • cairn add f1 f2 f3 — per-file progress, then one bundle URL.
  • cairn ls — the Bin as a TUI: ↑/k ↓/j / filter enter open s share q quit.
SPEC-0008The cairn Command-Line Interface →
The cairn ls terminal UI listing four artifacts in the Bin — a markdown audit, a Python script, a PNG and a live webhook endpoint — each with a type badge, a one-line description, and a provenance line reading "claude · via mcp" with an age, comment and reaction counts. A key hint bar along the bottom shows the navigation, filter, open, share and quit bindings.

Your agent, authorized

Cairn is an MCP server with OAuth, not a bolted-on API key. Your agent consents once to three scopes and then reads, creates, comments and reacts as you — including tailing live webhook and trace streams.

  • Read artifacts you can access.
  • Create and push new artifacts.
  • Comment and react on your behalf — revocable at any time in settings.
SPEC-0007MCP Server and OAuth Authorization →
The Cairn MCP authorization screen: "Claude Desktop wants to connect to your Cairn workspace over MCP", the signed-in account, and a list of the three scopes being granted — read artifacts you can access, create and push new artifacts, comment and react on your behalf — above Cancel and Authorize buttons and a note that access is revocable in settings.

◇  THE PROMISES · TRUE OF EVERY ARTIFACT

The same four guarantees, whatever you dropped

Provenance, a visible expiry, an access policy you can read, and one annotation layer — on every share type and on every surface.

Who made this, and how

Every artifact records its origin — human or model, through which channel, and when it was captured: claude · sonnet-4.6 · via MCP · captured 2h ago.

Ephemeral by default

A visible TTL on every share — expires in 5d — and a hard delete when it runs out. Nothing lingers because someone forgot it existed.

Link-based access

Capability URLs, with the policy on screen rather than buried in a menu: you + anyone with link.

One annotation layer

Reactions and threads with type-specific anchors — a block, a code line, an image region, a captured request, a span — and the same layer over MCP.

◇ THE DESIGN RECORD

Everything above was decided in public.

The decision records, the capability specifications and their RFC-2119 requirements — with the rejected options still in them — are published on this site in full, generated straight from the repository. No account, no forge, no hop off the page.

21decisions
15capability specs
253requirements
446scenarios
Read the decisionsBrowse the specsStart with the overview