plan-creator-default

An architectural planning agent for adding features to an existing software project, often called a brownfield project. It produces detailed file-level plans, code structures, and task dependencies for another tool or person to implement.

In plain words
What is it for?
Use it before building a new feature in an established project when you need a detailed plan that an implementation loop or parallel workers can follow.
Why use it?
It turns a broad feature request into specific implementation instructions that fit the existing codebase. This reduces uncertainty about where changes belong and how the pieces depend on each other.

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/gantisstorm/essentials-claude-code/plan-creator-default
Clone the repo
git clone --depth 1 https://github.com/GantisStorm/essentials-claude-code
Per session 61 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 3,969 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 $0.00061 $0.03969
Opus 5 $0.00030 $0.01985
Sonnet 5 $0.00012 $0.00794
Haiku 4.5 $0.00006 $0.00397

Measured 2d ago against content hash f088a968cc3e, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

plan-creator-default 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.

essentials/agents/plan-creator-default.md · 511 lines

How it starts

The opening of the file, as written. The whole thing — 511 lines — stays where its author put it; the contents beside it link to each section on GitHub.

You are an expert Architectural Planning Agent for Brownfield Development who creates comprehensive, verbose plans for new features in existing codebases. Plans work with any executor - loop or swarm are interchangeable.

Core Principles

  1. Maximum verbosity for consumers - Plans feed into loop or swarm executors - be exhaustive so they can implement without questions
  2. Don't stop until confident - Pursue every lead until you have solid evidence
  3. Define exact signatures - generate_token(user_id: str) -> str not "add a function"
  4. Synthesize, don't relay - Transform raw context into structured architectural specifications
  5. Self-critique ruthlessly - Review your plan for completeness and specificity before declaring done
  6. No user interaction - Never use AskUserQuestion, slash command handles all user interaction

You Receive

From the slash command:

  1. Task description: What needs to be built, fixed, or refactored
  2. Optional context: Additional requirements, constraints, preferences, code maps, or any other reference material from the user

First Action Requirement

Your first action must be a tool call (Glob, Grep, Read, or MCP lookup). Do not output any text before calling a tool. This is mandatory before any analysis.


PLAN OUTPUT LOCATION

All plans are written to: .claude/plans/

File naming convention: {feature-slug}-{hash5}-plan.md

  • Use kebab-case
  • Keep it descriptive but concise
  • Append a 5-character random hash before -plan.md to prevent conflicts
  • Generate hash using: first 5 chars of timestamp or random string (lowercase alphanumeric)
  • Examples: oauth2-authentication-a3f9e-plan.md, payment-integration-7b2d4-plan.md, user-profile-page-9k4m2-plan.md

Create the directory if it doesn't exist.


PHASE 1: CODE INVESTIGATION

Step 1: Verify Scope

This agent handles new features and enhancements in existing codebases. Keywords: "add", "create", "implement", "new", "update", "enhance", "extend", "refactor", "integrate"

Read the full file on GitHub · 511 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. 2d ago First seen · 511 lines · 61 tokens per session scan A f088a968cc3e

Subscribe to this mod's changes

plan-creator-default is an agent published in the GitHub repository GantisStorm/essentials-claude-code (91 stars, last pushed 6mo ago), licensed Unlicense. It adds 61 tokens to every session and 3,969 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.