agents-md

AGENTS.md read the way Claude Code reads CLAUDE.md, as a plugin, under one option, instructionFiles:

• claude-md: only CLAUDE.md is loaded, by the engine, as today. The plugin adds nothing.
• claude-md-or-agents-md (the default): a project with no instruction files of its own gets its AGENTS.md files instead, loaded exactly where and how CLAUDE.md would be. "Of its own" is read off what the engine loaded for the context: a CLAUDE.md, .claude/CLAUDE.md or CLAUDE.local.md in any directory from the root down to the working directory leaves the whole project to the engine, and the plugin stays out (the organization's managed file, the person's ~/.claude/CLAUDE.md, a .claude/rules file and an added directory's CLAUDE.md do not count, as the nested walk does not see them either). With none, every AGENTS.md and .claude/AGENTS.md on that path joins the instruction files the engine renders, and a Read under a subdirectory attaches that directory's AGENTS.md unless a CLAUDE.md there claims it.
• claude-md-and-agents-md: every AGENTS.md is loaded beside CLAUDE.md, up and down the tree; a file CLAUDE.md already @-imports, or is a link to, is not loaded a second time (compared by path, then by content).
• managed-only: the project's checked-in and private instruction files and the person's own are dropped from the context; the organization's managed CLAUDE.md and the engine's memory stay. The engine's nested CLAUDE.md attachments on Read are not an event yet and still arrive. (The engine's claudeMdExcludes setting also exists, for user, project and local files, and applies to the AGENTS.md files this plugin reads too.)

How the files reach the model is the engine's doing, not the plugin's: prompt.context hands a hook the instruction files behind claudeMd ({ path, kind, content, parent? }, kinds managed, user, project, local, memory, in load order) and a hook answers the list changed. The engine then renders claudeMd from the answered files with its own preamble and framing, announces them by name, and keeps only the managed ones for an agent that omits project instructions (Explore, Plan, a custom agent with omitClaudeMd). So an AGENTS.md this plugin adds as a project file is, to everything downstream, a project instruction file: same place in the context, same framing, same omission rules, same announcement. An organization's prepended plugin on prompt.context sits above this one and has the last word on the files.

hooks/register.ts is the module; everything under hooks/ is its parts, importing claude-code and one another alone. tests/ runs under claude plugin test <this folder>.

Setting the option

As a built-in its option is the /config row "Project instructions", a picker over the four values, each described there. By hand it is

{
  "pluginConfigs": {
    "agents-md@builtin": {
      "options": { "instructionFiles": "claude-md-and-agents-md" }
    }
  }
}

in user settings (~/.claude/settings.json), --settings, or managed settings; a project's .claude/settings.json is not read for plugin options. Changing it reloads the module, and the next context the engine builds (the next turn after the reload, a new conversation, /clear, a compaction) carries the new mode's files. A hand-typed value outside the four is told once in the transcript and reads as the default. /plugin lists the plugin among the built-ins, where a person can turn it off; with it off the engine reads CLAUDE.md alone. No hooks setting or CLI mode turns it off (disableAllHooks, allowManagedHooksOnly and --bare govern settings hooks and installed plugins, not built-ins); where the engine loads no instruction files (--bare without --add-dir, --safe-mode, CLAUDE_CODE_DISABLE_CLAUDE_MDS) its walk finds none and it adds none, CLAUDE.md and AGENTS.md alike.

The option was first keyed projectInstructions, with the values claude, agents-fallback, both and none. A value still stored under that key is honoured for now while instructionFiles reads as its default: none as managed-only, claude as claude-md, agents-fallback as claude-md-or-agents-md, both as claude-md-and-agents-md, any other value as claude-md (which adds nothing, never as the default, which loads AGENTS.md); the first session.start of a load says in the transcript how it was read. Once instructionFiles is set to anything but its default, the old key is not read and the transcript says to remove it.

Run from this folder instead (claude --plugin-dir mods/agents-md), the same entry is keyed "agents-md".

What it hooks

event	what the hook does
session.start	in every mode: passes the start straight through and floats the usage row for the configured mode, never awaited; the first start of a load logs how a stored projectInstructions value is read. The session's start never waits on this plugin
prompt.context	under claude-md-or-agents-md and claude-md-and-agents-md: walks $.fs.ancestors for the AGENTS.md files above the working directory and answers them as project instruction files, each @ import its own entry after its file, each placed where a project file of its directory stands (root first, before the first deeper project file, else after the last project file, before memory); files the engine already holds by path or by content are left out; under claude-md-or-agents-md it answers nothing when the project has a CLAUDE.md of its own (among the handed files, else found by a $.fs.ancestors walk, so a CLAUDE.md the engine loaded and then withheld still counts), and names the files it loaded in the debug log ($.ui.log with to: "debug": no CLAUDE.md found; AGENTS.md loaded: <paths>, nothing in the transcript) once, and again after a move to another project root; handed unknown files (a hook above rewrote the claudeMd text) it adds nothing; the first context of a load sends the load row (counts) and the feature mark; under managed-only (matcher: a project, local or user file present): answers the list without those kinds
agent.spawn on fork: true	under claude-md-or-agents-md and claude-md-and-agents-md: a fork the Agent tool starts shares its parent's prompt prefix, so the parent loop's delivered nested files are copied to the fork's loop and not attached to it again (a /fork or /subtask fork does not raise agent.spawn yet and starts from an empty set, as every fork did before; a fork started in the same tool batch as a Read inherits that Read's file although its prefix holds a placeholder for it)
tool.call on Read	under claude-md-or-agents-md and claude-md-and-agents-md, for a file under the session's project root ($.session.root(), read live, so /cd, a host's directory change and worktree moves are followed and a moved root starts the delivered sets and the fallback decision over; a file elsewhere gets nothing, as the engine attaches no nested CLAUDE.md there; and nothing anywhere in a run where the engine attaches nothing to a turn, --bare with its CLAUDE_CODE_SIMPLE or CLAUDE_CODE_DISABLE_ATTACHMENTS, read on every Read through $.env.get as the engine reads them on every turn): walks only the directories strictly between the root and the read file ($.fs.ancestors with below: root, as the engine walks only those for a nested CLAUDE.md, never up to the filesystem root again) and attaches their AGENTS.md files not yet given to that agent loop, not already among the context's instruction files (by path or, for a project file, by text) and not claimed by a CLAUDE.md of the same directory (or imported by one), as context after the tool result, framed Contents of <path>: byte for byte as the engine frames a nested CLAUDE.md, whatever its size; each file once per loop and conversation (the context's recomputation after a compaction or /clear starts the count over), the context's files never; a Read that attached files sends the nested row. A ~ or ~/ path is read under the home directory as the Read tool reads it

What it calls on $

fs.ancestors (with each found file's parts: the file and its imports apart; with below on a Read; it finds nothing on a thin client, whose workspace files are remote, as the engine's own walk does), session.root, session.cwd, env.get (HOME and USERPROFILE, once per load, the profile first on a Windows spelling of the working directory, so a ~/ path the model hands a Read resolves where the Read tool reads it; CLAUDE_CODE_SIMPLE and CLAUDE_CODE_DISABLE_ATTACHMENTS on every Read), ui.log, telemetry.log and telemetry.mark.

$.telemetry is the telemetry plugin's noun; where that plugin is not seated the calls find no noun and are dropped without a trace, and nothing else changes.

What it logs

Counts and closed choices only; no path and no file text. Each row goes through $.telemetry.log, so it exists only where the telemetry plugin does:

event	when	properties
agents_md_mode	once per fresh load, at session.start	mode (claude-md | claude-md-or-agents-md | claude-md-and-agents-md | managed-only), is_interactive
agents_md_load	the first context of a load, under claude-md-or-agents-md and claude-md-and-agents-md	mode, file_count (AGENTS.md files handed to the engine), import_count (their @ imports), total_content_length, yielded (claude-md-or-agents-md stood down for a CLAUDE.md of the project's own), walk_failed; with it one $.telemetry.mark for feature agents_md: ok, or sad with reason walk_failed
agents_md_nested	a Read that attached nested files	mode, file_count

Where it still differs from CLAUDE.md

All of these apply only to the modes that load AGENTS.md, claude-md-or-agents-md (the default) and claude-md-and-agents-md. Each names a loader fact a plugin cannot reach through the events it has today.

1. Nested files attach on a text Read only. The engine also attaches a directory's CLAUDE.md for a file @-mentioned in the prompt, for the IDE's opened file or selection, and for the Read tool's notebook, image and PDF results.
2. A nested file the plugin attaches is not registered in the loop's read-file state, so after a compaction the engine does not restore it among the recently read files (the plugin attaches it again at the next Read under that directory instead), and a change to it mid-session is not re-announced.
3. /cd carries the new tree's CLAUDE.md in its own notice; the plugin's files for the new tree arrive in the same next request through the engine's instructions announcement instead.
4. Paths compare by spelling; the engine resolves a symlinked alias of the working directory before deciding a file is inside it.
5. --add-dir directories contribute no AGENTS.md, where the engine can load their CLAUDE.md.
6. /memory and the # shortcut do not know AGENTS.md files, and the engine's own initial-load row does not count them (this plugin's agents_md_load row does).
7. An @ import outside the working directory inside an AGENTS.md is honoured only once the approval the engine asks for a CLAUDE.md's external imports has been given (without it the import is left out, as a CLAUDE.md's is); the approval dialog itself is raised for CLAUDE.md imports alone.
8. A subagent that is not a fork gets a nested AGENTS.md at its own first Read under that directory even when its parent's loop was already given it; the engine does not hand such a subagent the nested CLAUDE.md again. A fork matches the engine on both sides.

Testing

claude plugin test mods/agents-md

tests/register.test.ts covers the default mode: a project with AGENTS.md alone gets it as a project instruction file and one debug-log line naming it, with nothing in the transcript, a project with a CLAUDE.md of its own is left to the engine without a walk, a failed walk leaves the context as handed, and the start hands $.telemetry the mode row alone where a test seats a provider for that noun, and goes on untouched where none is seated.