codex/codex-rs/execpolicy/README.md

codex-execpolicy

Overview

• Policy engine and CLI built around prefix_rule(pattern=[...], decision?, match?, not_match?).
• This release covers the prefix-rule subset of the execpolicy language; a richer language will follow.
• Tokens are matched in order; any pattern element may be a list to denote alternatives. decision defaults to allow; valid values: allow, prompt, forbidden.
• match / not_match supply example invocations that are validated at load time (think of them as unit tests); examples can be token arrays or strings (strings are tokenized with shlex).
• The CLI always prints the JSON serialization of the evaluation result.
• The legacy rule matcher lives in codex-execpolicy-legacy.

Policy shapes

• Prefix rules use Starlark syntax:

prefix_rule(
    pattern = ["cmd", ["alt1", "alt2"]], # ordered tokens; list entries denote alternatives
    decision = "prompt",                 # allow | prompt | forbidden; defaults to allow
    match = [["cmd", "alt1"], "cmd alt2"],           # examples that must match this rule
    not_match = [["cmd", "oops"], "cmd alt3"],       # examples that must not match this rule
)

CLI

• From the Codex CLI, run codex execpolicy check subcommand with one or more policy files (for example src/default.codexpolicy) to check a command:

codex execpolicy check --policy path/to/policy.codexpolicy git status

• Pass multiple --policy flags to merge rules, evaluated in the order provided, and use --pretty for formatted JSON.
• You can also run the standalone dev binary directly during development:

cargo run -p codex-execpolicy -- check --policy path/to/policy.codexpolicy git status

• Example outcomes:
  • Match: {"match": { ... "decision": "allow" ... }}
  • No match: {"noMatch": {}}

Response shapes

• Match:

{
  "match": {
    "decision": "allow|prompt|forbidden",
    "matchedRules": [
      {
        "prefixRuleMatch": {
          "matchedPrefix": ["<token>", "..."],
          "decision": "allow|prompt|forbidden"
        }
      }
    ]
  }
}

• No match:

{"noMatch": {}}

• matchedRules lists every rule whose prefix matched the command; matchedPrefix is the exact prefix that matched.
• The effective decision is the strictest severity across all matches (forbidden > prompt > allow).

Note: execpolicy commands are still in preview. The API may have breaking changes in the future.