A mention in one document that points to another, so the agent can pull it into the context window only when the task calls for it. The unit progressive disclosure is built from.
The reason to use a pointer (instead of inlining the content) is cost. A pointer is one line in the context window. The document behind it might be thousands of tokens, but those tokens cost nothing until the agent actually follows the pointer. Inline a 2,000-token runbook in AGENTS.md and every session pays for it; replace it with "deploy process: see internal/deploy.md" and only the sessions that deploy ever load it. The agent follows the pointer with a tool call when the task matches.
A pointer needs two parts to work: a stable path, and enough description for the agent to know when following it is worth it. A bare path is a pointer the agent has no reason to follow; "see internal/deploy.md" with no hint of what's inside gets skipped by a session that needed it. Write the line so it matches how tasks present: "release, deploy, or rollback — read internal/deploy.md first".
Pointers are everywhere once you look: lines in AGENTS.md, skill descriptions (the harness loads the description; the skill body waits behind it), filenames in a directory listing, links between docs.
A pointer can also tie a secondary source back to the primary source it was derived from — the compaction summary that names the original transcript, the doc that names the source file it describes. This makes the secondary source's lossiness recoverable: when the summary turns out not to be enough, the agent follows the pointer and reads the original, instead of working from whatever the summary kept.
Avoid: "reference" — too dry; doesn't convey that following it pulls more context in. "Portal" — too florid.
Usage:
"AGENTS.md is getting huge."
"Most of it should be context pointers, not content. Keep the always-on rules inline; turn the deploy runbook and the style guide into skills and leave a context pointer behind."