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.
npx agentmods add skills/sd0xdev/sd0x-harness/codex-implementnpx skills add sd0xdev/sd0x-harness --skill codex-implementgit clone --depth 1 https://github.com/sd0xdev/sd0x-harnessWhat 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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5 | $0.00058 | $0.01297 |
| Opus 5 | $0.00029 | $0.00648 |
| Sonnet 5 | $0.00012 | $0.00259 |
| Haiku 4.5 | $0.00006 | $0.00130 |
Grade A, and why
codex-implement 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 2d 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.
How it starts
The opening of the file, as written. The whole thing — 161 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Codex Implement Skill
Trigger
- Keywords: codex implement, implement feature, codex write code, implement from spec
When NOT to Use
- Architecture advice only (use
/codex-architect) - Code review (use
/codex-review-fast) - Bug fix (use
/bug-fix) - Simple one-line change (edit directly)
Workflow
Parse args → Decompose → Collect context → Iterate items → Review loop → Done
↕
codex → diff → confirm
↕
reject/modify → codex-reply
Step 1: Parse & Decompose
--spec provided: Read spec/request doc, extract individual items.
Arguments without --spec: Use directly as single item.
No arguments: Ask user for requirement, target file, reference files.
Intent check: identify the feature this work belongs to (from the spec, the task, or the
paths) and read docs/features/<key>/intent-<key>.md if it exists — its INV-* invariants and
Non-goals constrain every item; a planned item that contradicts one stops and asks the user
(cite the line). No identifiable feature → nothing to load; proceed.
Break into implementation items — each one logical unit (interface, method, endpoint), implementable in dependency order, small enough for one Codex call.
Present plan before starting:
| # | Item | Target File | Depends On |
|---|-------------------|----------------------|------------|
| 1 | Define interfaces | src/interface/x.ts | - |
| 2 | Core logic | src/service/x.ts | 1 |
| 3 | Controller/Route | src/controller/x.ts | 2 |
Proceed?
Step 2: Collect Context (Claude, NOT Codex)
Claude researches the codebase before calling Codex:
- Read
.claude/CLAUDE.md(fallbackCLAUDE.md) — tech stack, conventions, test commands - Read target file (if exists) and context files
- Search similar implementations
- Read 2-3 similar files for patterns
What ships with it
1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
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.
- 2d ago First seen · 161 lines · 58 tokens per session scan A d05adc27e759
codex-implement is a skill published in the GitHub repository sd0xdev/sd0x-harness (188 stars, last pushed 2d ago), licensed MIT. It adds 58 tokens to every session and 1,297 once invoked, about $0.0003 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 2026-08-30.
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