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Michael Bolin cafb07fe6e feat: add justification arg to prefix_rule() in *.rules (#8751 )

Adds an optional `justification` parameter to the `prefix_rule()`
execpolicy DSL so policy authors can attach human-readable rationale to
a rule. That justification is propagated through parsing/matching and
can be surfaced to the model (or approval UI) when a command is blocked
or requires approval.

When a command is rejected (or gated behind approval) due to policy, a
generic message makes it hard for the model/user to understand what went
wrong and what to do instead. Allowing policy authors to supply a short
justification improves debuggability and helps guide the model toward
compliant alternatives.

Example:

```python
prefix_rule(
    pattern = ["git", "push"],
    decision = "forbidden",
    justification = "pushing is blocked in this repo",
)
```

If Codex tried to run `git push origin main`, now the failure would
include:

```
`git push origin main` rejected: pushing is blocked in this repo
```

whereas previously, all it was told was:

```
execpolicy forbids this command
```

2026-01-05 21:24:48 +00:00

2.9 KiB

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codex-execpolicy

Overview

Policy engine and CLI built around prefix_rule(pattern=[...], decision?, justification?, 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.
justification is an optional human-readable rationale for why a rule exists. It can be provided for any decision and may be surfaced in different contexts (for example, in approval prompts or rejection messages). When decision = "forbidden" is used, include a recommended alternative in the justification, when appropriate (e.g., "Use `jj` instead of `git`.").
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
    justification = "explain why this rule exists",
    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.rules) to check a command:

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

Pass multiple --rules 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 --rules path/to/policy.rules git status

Example outcomes:
- Match: {"matchedRules":[{...}],"decision":"allow"}
- No match: {"matchedRules":[]}

Response shape

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

When no rules match, matchedRules is an empty array and decision is omitted.
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.

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codex-execpolicy

Overview

Policy shapes

CLI

Response shape

2.9 KiB

Raw Permalink Blame History