Codex Model Catalog Config

Modify only the user's existing default.json catalog according to the explicit request. Treat the catalog as the source of truth.

Do not inspect or modify config.toml, even if it appears to be missing the catalog setting. Do not create or restore the catalog from the bundled asset during normal model management. Do not create a backup of the old catalog.

Target File

Resolve the Codex home directory in this order:

• Use CODEX_HOME when it is set.
• On Windows, default to %USERPROFILE%\.codex.
• On macOS, default to $HOME/.codex.

The target is exactly:

<CODEX_HOME>/model-catalogs/default.json

If the target does not exist, stop and report that path. Do not search for another catalog or create a replacement elsewhere.

Efficiency Rules

Each entry embeds very large base_instructions / model_messages strings. Never read or print the whole file into the response.

• Inspect with one compact probe that lists only slug, context_window, max_context_window, default_reasoning_level, and whether tool_mode is present. Do not echo base_instructions or model_messages.
• Do not read the raw file and then inspect it a second time. One probe answers both "does the slug already exist" and "which entry do I clone".
• Make the edit in memory and write once. Do not stage intermediate copies or temp files.
• Locate an entry by its "slug" line and the surrounding object braces; do not enumerate every field.
• Keep round trips minimal: one probe, then one write-and-validate step.

Workflow

1. Run one compact probe to confirm the file exists, confirm a top-level models array, list the current slugs, and capture only the fields the request needs.
2. Follow the user's written request only. Do not add unrelated validation, repairs, settings changes, or files.
3. For an added model, ask only for model-specific values that the user omitted. Clone a compatible existing entry when one is available, then change only the requested fields. Reject a duplicate slug.
4. Do not add tool_mode to a new entry. If the chosen source entry has tool_mode, remove it from the new entry even though the source model remains unchanged.
5. For a modified model, require an exact existing slug and change only the requested fields. Preserve every other model and field.
6. For a deleted model, remove only the explicitly named entry. Otherwise, preserve the order and contents of all remaining models.
7. Write the minimal change directly to default.json in a single in-memory edit. Preserve the existing JSON indentation, encoding, newline style, and unrelated content.
8. Re-parse the written file and confirm that the top-level models array is valid and that the intended entries are present. Do not perform unrelated checks.

Do not run the models. Do not call codex exec, codex, or any provider request as part of this skill.

Reporting

Tell the user:

• The default.json path that was modified.
• The model slugs added, changed, or removed.
• The fields changed for each model.
• That the written file parses as valid JSON.

Do not claim that a model works or that a provider supports it. A catalog entry is a local list entry, not proof of provider availability or entitlement.

Boundaries

• Write only default.json. Do not create backups, temp files, or any other file during the change.
• Never modify config.toml.
• Never create a timestamped or other backup of default.json.
• Never replace the user's catalog with assets/default.json.
• Do not require Python, Node.js, or a management script.
• Do not expose credentials or include secrets in output.