How to Choose Safe Codex Subagents
Choose a bounded job, inspect actual permissions and require evidence before relying on a delegated result.
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Start with the work that can be separated
A useful specialist has one clear question and an output the parent can check. For a bug fix, mapping a relevant code path and reviewing a supplied patch can be separate tasks. Two agents independently rewriting the same files create a different coordination problem. Begin with a small scope rather than a long catalog of impressive role names.
Here, safe means a more controlled selection and review process. No role name, instruction file or tool can guarantee an agent will never make a mistake. Match the data and action permissions to the job, and keep responsibility for the final decision with the person or parent workflow.
Know the technical boundary
The official subagent documentation states that custom agents inherit the parent permissions, provider and MCP configuration. A custom file can reduce supported capabilities; a written request to avoid edits does not create a separate read-only sandbox. Choose the parent permission mode before delegation.
Current documentation uses standalone custom-agent TOML files with a name, description and developer instructions. Check the installed client before using a file from an older collection. The configuration reference describes current settings and legacy aliases. Documentation checked October 15, 2026.
Review a candidate before using it
| Question | What to inspect | Reason to pause |
|---|---|---|
| Who maintains it? | Repository owner, license, specific commit or release, recent changes. | Unclear origin or a bundle that changes without review. |
| What will it do? | The full instructions and referenced files. | A narrow description hides installation or publishing steps. |
| What can it access? | Parent permissions, tools, connectors and selected data. | The job needs little data but the environment exposes much more. |
| What can it change? | File writes, network calls, credentials and external actions. | A review role is told to alter production or send private data. |
| How will it report? | Evidence references, checks actually run and unresolved issues. | It is instructed to claim success without examining the result. |
A bounded review example
Suppose a change fixes an empty-search result. Ask a reviewer to inspect the supplied patch, the relevant caller and tests, and return concrete correctness findings with file references. Explicitly exclude unrelated modules, credentials and external publishing. Keep implementation separate until the evidence is reviewed.
For a static review, disabling shell execution and unnecessary connected capabilities can reduce the available surface. If running tests is part of the actual question, decide the necessary environment and permissions before the task begins. Do not describe an instruction-only restriction as a technical control.
Build a file you can review
Use the Codex Subagent Configuration Builder to choose a focused role, enter the allowed scope and question, and set a return format. It leaves model settings inherited and offers supported capability reductions. Read the resulting TOML before downloading.
The tool does not install the file or start an agent. Compare it with your client schema, choose the parent permissions and supply a bounded handoff when you decide to use it. Keep a copy of the reviewed version so a later change to the instructions does not silently change the task you approved.
Accept evidence rather than confidence
- Check that the result answers the original question and stays inside the stated scope.
- Follow important file references and reproduce a critical finding where practical.
- Separate a code reading, a passing test and a verified production result; they establish different things.
- Ask which files, settings and cases were not examined. An honest limitation is useful information.
- Review changes before merging or publishing. A specialist summary is an input to that decision.
When one agent is enough
Keep short dependent work together when dividing it would create more handoff effort than value. Delegation is useful when independent evidence can be gathered in parallel; it is not a quality badge. Use fewer overlapping roles and a clear final reviewer instead of assuming that more agents mean more certainty.
If a candidate includes a skill bundle, inspect its scripts and dependencies with the skill-audit method and the local text checker. A clean text report still needs a provenance and behavior review.
Frequently asked questions
Does calling an agent a reviewer make it read-only?
No. Instructions and technical permissions are different. Inspect the parent environment and available capabilities.
Should I copy every role from a public collection?
Choose only the roles useful for your task, inspect their exact files and preserve the reviewed version.
Does this article activate agents?
No. It explains selection and review. The linked builder creates text only.
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