codex-plan-apply

codex-plan-apply is a skill for Claude Code, Codex from blake-simpson/belmont. It costs 45 tokens per session (768 once invoked), scanned A, original, Apache-2.0.

A compatibility step that writes approved Belmont planning files after a plan interview. Belmont is a planning workflow that stores product and technical plans in `.belmont/` files.

In plain words
What is it for?
Apply a supplied `BELMONT_PLAN_PACKET` by creating or updating only the named planning files, without editing source code.
Why use it?
It preserves an already-approved plan without restarting the interview or accidentally inventing missing requirements.

Skill for Claude CodeCodex

Part of the belmont plugin — 17 skills, 6 agents shipped together

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/blake-simpson/belmont/codex-plan-apply
Any agent
npx skills add blake-simpson/belmont --skill codex-plan-apply
Clone the repo
git clone --depth 1 https://github.com/blake-simpson/belmont

Made for: Claude Code, Codex.

Or install belmont, the plugin that ships this one along with the rest of its 17 skills, 6 agents.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for codex-plan-apply

README.md
[![agentmods](https://agentmods.dev/badge/skills/blake-simpson/belmont/codex-plan-apply.svg)](https://agentmods.dev/skills/blake-simpson/belmont/codex-plan-apply)
Your own site
<a href="https://agentmods.dev/skills/blake-simpson/belmont/codex-plan-apply"><img src="https://agentmods.dev/badge/skills/blake-simpson/belmont/codex-plan-apply.svg" alt="Measured on agentmods" height="20"></a>
Per session 45 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 768 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00045 $0.00768
Opus 5 $0.00023 $0.00384
Sonnet 5 $0.00009 $0.00154
Haiku 4.5 $0.00005 $0.00077

Measured 4d ago against content hash 1d46e1852596, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

codex-plan-apply scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 4d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

plugin/skills/codex-plan-apply/SKILL.md · 85 lines

How it starts

The opening of the file, as written. The whole thing — 85 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Belmont: Codex Plan Apply

Use this skill only when the user provides a BELMONT_PLAN_PACKET produced by a Codex plan-mode Belmont planning session.

This is a Codex compatibility adapter. Other agents that can ask structured questions and write files in the same session should keep using product-plan and tech-plan directly.

Purpose

Codex plan mode provides keyboard-navigable structured questions, but may not be the right phase for writing planning files. This skill runs after the user leaves plan mode. It persists the already-approved planning output without reopening the interview.

Rules

  1. Do NOT ask product or technical planning questions.
  2. Do NOT infer missing PRD, PROGRESS, TECH_PLAN, or models.yaml content.
  3. Do NOT edit source code.
  4. Only write files under .belmont/.
  5. Only write, create, or update files explicitly listed in the packet.
  6. Preserve existing content unless the packet explicitly says a file should be replaced.
  7. For update operations, edit the named sections only. Never replace a real existing file unless the packet explicitly marks it as a full-file replacement.
  8. If the packet is incomplete, ambiguous, malformed, or lacks target paths, stop and ask the user to rerun the relevant Codex plan-mode skill.

Expected Packet Shape

The packet is plain Markdown in a fenced block:

```BELMONT_PLAN_PACKET
kind: product-plan | tech-plan
mode: create | update
feature_slug: <slug or none>
base_path: .belmont/features/<slug> | .belmont

files:
  - path: .belmont/features/<slug>/PRD.md
    operation: create | replace | update-section
    content: |
      ...
  - path: .belmont/features/<slug>/PROGRESS.md
    operation: create | replace | update-section
    content: |
      ...

post_apply:
  commit_message: belmont: update planning files after product planning
  next_prompt: /plan $belmont:tech-plan <feature>
```

YAML-like structure is preferred, but exact YAML parsing is not required. The key requirement is that each file path, operation, and content block is explicit enough to apply safely.

Read the full file on GitHub · 85 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 4d ago First seen · 85 lines · 45 tokens per session scan A 1d46e1852596

Subscribe to this mod's changes

codex-plan-apply is a skill published in the GitHub repository blake-simpson/belmont (4 stars, last pushed 16d ago), licensed Apache-2.0. It adds 45 tokens to every session and 768 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

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