codex-implementer

An agent that uses the Codex command-line tool to implement requested code changes, then seeks confirmation before a review step.

In plain words
What is it for?
Use it to inspect target and related files, follow existing project patterns, generate feature code, show the diff, and run a follow-up review after approval.
Why use it?
It provides a defined path from requirements and project context to implementation, with options to accept, reject, or revise the changes.

Agent

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 agents/sd0xdev/sd0x-harness/codex-implementer
Clone the repo
git clone --depth 1 https://github.com/sd0xdev/sd0x-harness
Per session 25 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 713 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 $0.00025 $0.00713
Opus 5 $0.00013 $0.00357
Sonnet 5 $0.00005 $0.00143
Haiku 4.5 $0.00003 $0.00071

Measured yesterday against content hash 3910a523074b, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

codex-implementer 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 yesterday.

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.

agents/codex-implementer.md · 132 lines

How it starts

The opening of the file, as written. The whole thing — 132 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Codex Implementer

Workflow

sequenceDiagram
    participant U as User
    participant A as Agent
    participant X as Codex
    participant R as Review

    U->>A: Requirement description
    A->>A: Collect context
    A->>X: codex exec (write)
    X-->>A: Changes complete
    A->>A: git diff
    A->>U: Confirm changes?
    alt Accept
        U-->>A: ✅
        A->>R: /codex-review-fast
        R-->>A: Review result
    else Reject
        U-->>A: ❌
        A->>A: git checkout
    else Modify
        U-->>A: 🔄 + suggestions
        A->>X: Regenerate
    end

Context Collection Strategy

1. Target File Analysis

If a target file is specified:

  • Read existing content
  • Analyze imports/dependencies
  • Understand existing structure

2. Related File Search

Search by requirement keywords:

# Search for similar implementations
grep -r "keyword" src/ --include="*.ts" | head -10

# Search for related services
find src/service -name "*.ts" | xargs grep -l "related feature"

3. Project Pattern Recognition

Identify and follow project patterns:

Pattern Files Description
Service src/service/*.service.ts Business logic
Provider src/provider/**/*.ts External service wrapper
Controller src/controller/*.controller.ts API endpoints
Config src/config/*.ts Configuration

Change Confirmation Flow

Display Changes

git diff --stat
git diff
git ls-files --others --exclude-standard  # New files

Confirmation Options

Option Action
✅ Accept Keep changes, run review
❌ Reject git checkout . && git clean -fd
🔄 Modify Collect suggestions, regenerate

Automatic Review

After accepting changes, must execute:

Read the full file on GitHub · 132 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. yesterday First seen · 132 lines · 25 tokens per session scan A 3910a523074b

Subscribe to this mod's changes

codex-implementer is an agent published in the GitHub repository sd0xdev/sd0x-harness (188 stars, last pushed 2d ago), licensed MIT. It adds 25 tokens to every session and 713 once invoked, about $0.0001 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.