fix: migrate to AGENTS.md (#764)

Migrate from `codex.md` to `AGENTS.md`

README.md

@@ -227,13 +227,13 @@ Key flags: `--model/-m`, `--approval-mode/-a`, `--quiet/-q`, and `--notify`.
 
 ## Memory & project docs
 
-Codex merges Markdown instructions in this order:
+You can give Codex extra instructions and guidance using `AGENTS.md` files. Codex looks for `AGENTS.md` files in the following places, and merges them top-down:
 
-1. `~/.codex/instructions.md` - personal global guidance
+1. `~/.codex/AGENTS.md` - personal global guidance
-2. `codex.md` at repo root - shared project notes
+2. `AGENTS.md` at repo root - shared project notes
-3. `codex.md` in cwd - sub-package specifics
+3. `AGENTS.md` in the current working directory - sub-folder/feature specifics
 
-Disable with `--no-project-doc` or `CODEX_DISABLE_PROJECT_DOC=1`.
+Disable loading of these files with `--no-project-doc` or the environment variable `CODEX_DISABLE_PROJECT_DOC=1`.
 
 ---
 
@@ -446,7 +446,7 @@ Below is a comprehensive example of `config.json` with multiple custom providers
 
 ### Custom instructions
 
-You can create a `~/.codex/instructions.md` file to define custom instructions:
+You can create a `~/.codex/AGENTS.md` file to define custom guidance for the agent:
 
 ```markdown
 - Always respond with emojis

codex-cli/src/cli.tsx

@@ -68,7 +68,7 @@ const cli = meow(
     --auto-edit                Automatically approve file edits; still prompt for commands
     --full-auto                Automatically approve edits and commands when executed in the sandbox
 
-    --no-project-doc           Do not automatically include the repository's 'codex.md'
+    --no-project-doc           Do not automatically include the repository's 'AGENTS.md'
     --project-doc <file>       Include an additional markdown file at <file> as context
     --full-stdout              Do not truncate stdout/stderr from command outputs
     --notify                   Enable desktop notifications for responses
@@ -144,7 +144,7 @@ const cli = meow(
       },
       noProjectDoc: {
         type: "boolean",
-        description: "Disable automatic inclusion of project-level codex.md",
+        description: "Disable automatic inclusion of project-level AGENTS.md",
       },
       projectDoc: {
         type: "string",

codex-cli/src/utils/config.ts

@@ -211,12 +211,22 @@ export type AppConfig = {
 export const PRETTY_PRINT = Boolean(process.env["PRETTY_PRINT"] || "");
 
 // ---------------------------------------------------------------------------
-// Project doc support (codex.md)
+// Project doc support (AGENTS.md / codex.md)
 // ---------------------------------------------------------------------------
 
 export const PROJECT_DOC_MAX_BYTES = 32 * 1024; // 32 kB
 
-const PROJECT_DOC_FILENAMES = ["codex.md", ".codex.md", "CODEX.md"];
+// We support multiple filenames for project-level agent instructions.  As of
+// 2025 the recommended convention is to use `AGENTS.md`, however we keep
+// the legacy `codex.md` variants for backwards-compatibility so that existing
+// repositories continue to work without changes.  The list is ordered so that
+// the first match wins – newer conventions first, older fallbacks later.
+const PROJECT_DOC_FILENAMES = [
+  "AGENTS.md", // preferred
+  "codex.md", // legacy
+  ".codex.md",
+  "CODEX.md",
+];
 const PROJECT_DOC_SEPARATOR = "\n\n--- project-doc ---\n\n";
 
 export function discoverProjectDocPath(startDir: string): string | null {
@@ -257,7 +267,8 @@ export function discoverProjectDocPath(startDir: string): string | null {
 }
 
 /**
- * Load the project documentation markdown (codex.md) if present. If the file
+ * Load the project documentation markdown (`AGENTS.md` – or the legacy
+ * `codex.md`) if present. If the file
  * exceeds {@link PROJECT_DOC_MAX_BYTES} it will be truncated and a warning is
  * logged.
  *