parallel-change

parallel-change is a command for coding agents from studioKjm/ai-harness-template. It costs 45 tokens per session (794 once invoked), scanned A, original, MIT.

A command-line planner for changing databases, APIs, or code interfaces without breaking the existing version. It uses three stages: expand, migrate, and contract.

In plain words
What is it for?
Use it to create and track migration plans, move traffic or data to the new version, and remove the old version after the change is safe.
Why use it?
It reduces downtime and service failures when a change is incompatible with the old interface.

Command

Part of the harness plugin — 44 commands, 11 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 commands/studiokjm/ai-harness-template/parallel-change
Clone the repo
git clone --depth 1 https://github.com/studioKjm/ai-harness-template

Or install harness, the plugin that ships this one along with the rest of its 44 commands, 11 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 parallel-change

README.md
[![agentmods](https://agentmods.dev/badge/commands/studiokjm/ai-harness-template/parallel-change.svg)](https://agentmods.dev/commands/studiokjm/ai-harness-template/parallel-change)
Your own site
<a href="https://agentmods.dev/commands/studiokjm/ai-harness-template/parallel-change"><img src="https://agentmods.dev/badge/commands/studiokjm/ai-harness-template/parallel-change.svg" alt="Measured on agentmods" height="20"></a>
Per session 45 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 794 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 5.1 $0.00045 $0.00794
Opus 5 $0.00023 $0.00397
Sonnet 5 $0.00009 $0.00159
Haiku 4.5 $0.00005 $0.00079

Measured 5d ago against content hash 0df2cbef5e4c, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-05, from the pricing page.

Security

Grade A, and why

parallel-change 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 5d 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.

methodologies/parallel-change/commands/parallel-change.md · 104 lines

How it starts

The opening of the file, as written. The whole thing — 104 lines — stays where its author put it; the contents beside it link to each section on GitHub.

/parallel-change — Plan Manager

호환 깨는 변경을 다운타임 0으로 처리하는 상태머신

When to use

  • DB 스키마 변경 (컬럼 타입·이름·제약 변경)
  • API 시그니처 변경 (필수 파라미터 추가/제거)
  • 함수/타입 시그니처 breaking change
  • /diff-spec이 🔴 Breaking-change indicator를 띄웠을 때

Prerequisites

  • Parallel Change methodology active: /methodology compose ouroboros parallel-change

Subcommands

/parallel-change new <id> [--title TITLE]    Create new plan in phase=expand
/parallel-change list                         List all plans + current phase
/parallel-change show <id>                    Print full plan

For phase transitions, use the dedicated commands:

  • /expand — register/verify expand phase
  • /migrate-traffic — advance to migrate
  • /contract — advance to contract

Instructions

Delegate to the Python script. Do not hand-edit plan YAML files — they are state-machine artifacts owned by the dispatcher.

Step 1 — Locate the script

.harness/methodologies/parallel-change/scripts/pc.py

Step 2 — Resolve subcommand

python3 .harness/methodologies/parallel-change/scripts/pc.py new <id> --title "<title>"
python3 .harness/methodologies/parallel-change/scripts/pc.py list
python3 .harness/methodologies/parallel-change/scripts/pc.py show <id>

Step 3 — Plan ID convention

Use pc-<YYYY-MM-DD>-<short-slug> format. Example:

pc-2026-04-28-refund-amount-enum
pc-2026-04-28-orders-api-v2

Step 4 — After creating a plan

Guide the user through the next step:

  1. Register the old signature (what's being replaced):

    pc.py set-old <id> --symbol "Refund.amount" --pattern 'Refund\.amount\b'
    
  2. Implement the new signature alongside the old, then register:

    pc.py set-new <id> --symbol "Refund.amount_type" --pattern 'Refund\.amount_type\b'
    
  3. When ready to transition: /migrate-traffic (will validate expand criteria)

Step 5 — Caller pattern guidance

The caller_pattern is a regex passed to ripgrep/grep. Common examples:

Target type Pattern example
Property access Refund\.amount\b
Function call \boldFunction\s*\(
API endpoint POST\s+/api/v1/refunds
DB column \brefunds\.amount\b
Type/Class name \bOldType\b

Read the full file on GitHub · 104 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. 5d ago First seen · 104 lines · 45 tokens per session scan A 0df2cbef5e4c

Subscribe to this mod's changes

parallel-change is a command published in the GitHub repository studioKjm/ai-harness-template (43 stars, last pushed 3mo ago), licensed MIT. It adds 45 tokens to every session and 794 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 2026-08-30.