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Two-Step Change Method · jabrena | DecimalAI

codingby jabrena

Two-Step Change Method

jabrena/051-design-two-steps-methods

Source jabrena/plinth ↗License Apache-2.0

Use when a complex or risky code change should be split into Kent Beck's two-step method by first making the change easy through behavior-preserving preparatory refactoring, then making the intended behavior change once the design supports it. This should trigger for requests such as Apply two-step change; Make this risky change safer; Refactor before changing behavior; Separate preparation from behavior change. Part of Plinth Toolkit

SkillScore77Maintained

Automatic

Coding pack

Last verified 8/20/2026

What it changes

Passed 16 of 21 test cases with the skill, and 3 of 21 without it.

Without skill14%

With skill77%

Checks it passed that the model alone missed

Keeps Step 1 strictly behavior-preserving by extracting methods.
Focuses Step 1 on introducing a notifier interface without adding Slack logic.
Recommends creating test seams during Step 1 without modifying inventory logic.

and 34 more in the full report

16 fixed1 passed either way3 still failing2 broke

Pass-rate lift: +64 pp
Tokens: -11%
Agent turns: 0%
Response time: -34%

Model gemini-3.6-flashMeasured 8/20/2026v117 of 22 cases passed with skill · 21 comparable

Tokens, turns and time describe resource use, not a dollar price.

Use this skill

Save it into your project's skills folder. Claude Code picks it up in its next session.

curl -fsSL --create-dirs -o .claude/skills/jabrena-051-design-two-steps-methods/SKILL.md https://app.decimal.ai/s/jabrena-051-design-two-steps-methods/SKILL.md

Want it pinned and updatable? pip install "decimalai>=0.15", then decimalai skills add jabrena-051-design-two-steps-methods, and start Claude Code with claude --plugin-dir "$(git rev-parse --show-toplevel)/.agents"

1 · One-time — install the CLI (docs ↗)

pip install "decimalai>=0.15"

2 · Get the skill — writes .agents/skills/jabrena-051-design-two-steps-methods/ and pins it in .decimal/skills.lock

decimalai skills add jabrena-051-design-two-steps-methods

No CLI? Get the same file — curl · raw file

curl -fsSL --create-dirs -o .claude/skills/jabrena-051-design-two-steps-methods/SKILL.md https://app.decimal.ai/s/jabrena-051-design-two-steps-methods/SKILL.md

Raw file: /s/jabrena-051-design-two-steps-methods/SKILL.md ↗ · machine-readable summary at /s/jabrena-051-design-two-steps-methods.json ↗

Safety checks: 3 of 3 passed

Code scan CleanIntent PassedContent Clean

See it in action

One of 15 test cases the skill fixed. Same model, same prompt, with and without the skill.

1 of 15

Prompt

I need to add support for a new third-party payment gateway in our legacy OrderProcessor.java class. Right now, all payment logic is hardcoded inside a 500-line method with high coupling. Can you walk me through planning and executing this modification safely so we don't break existing functionality while introducing the new gateway?

What was checked, without and with the skill
Checked	Without skill	With skill
Explicitly defines the intended behavior change before describing any preparatory refactoring.	Missed	Passed
Isolates Step 1 as purely behavior-preserving refactoring.	Passed	Passed
Requires running existing tests after Step 1 before making Step 2 behavior changes.	Passed	Passed

case-01 · gemini-3.6-flash · 8/20/2026 · answers are capped and redacted

What's inside

The instructions your model reads when the skill loads.

SKILL.md62 lines2 files

Two-Step Change Method

Guide Java developers through complex or risky changes by keeping design preparation separate from behavior modification. This is an interactive SKILL.

What is covered in this Skill?

Clarifying the intended behavior change before editing
Identifying design obstacles that make the change difficult or risky
Step 1: behavior-preserving preparatory refactoring that makes the change easy
Validation that Step 1 preserves existing behavior
Step 2: the smallest intended behavior change after the design supports it
Verification that Step 2 delivers the intended behavior
Handoff to focused Java, framework, persistence, messaging, API, or testing skills while preserving the two-step sequence

Constraints

Separate behavior-preserving preparation from behavior-changing work, and validate after each step.

MUST: State the intended behavior change before proposing preparatory refactoring
MUST: Keep Step 1 behavior-preserving; do not mix broad refactoring with the intended behavior change
MUST: Verify existing behavior after Step 1 using the project-appropriate tests, build, characterization tests, or manual checks
MUST: Make Step 2 only after the design has been prepared and validated
MUST: Verify the intended behavior after Step 2 with focused tests and relevant build checks
MUST: Record assumptions and risks when preparation cannot be fully separated from behavior change

When to use this skill

Apply two-step change
Make this risky change safer
Refactor before changing behavior
Separate preparation from behavior change
Make the change easy, then make the easy change

Workflow

Define the intended change

Read references/051-design-two-steps-methods.md, inspect the relevant code and tests, and state the exact behavior or capability that must change. Identify why the current design makes the change complex, risky, or hard to verify.

Plan preparatory refactoring

Track record

Benchmark

16 / 21

test cases passed, vs 3 / 21 without

Adoption

Users: 0
Times used: 0

Safety and source details

SkillSafety

✓ 3 of 3 passed

Code scan15 of 15 checks clean

0 critical · 0 warning · 0 info — scanner v4 — 8/3/2026

View 15 scanner checks

live_secretremote_code_executionreverse_shelldata_exfiltrationssrf_metadataagent_snoopinganti_refusaldestructive_commandsobfuscated_unicodeunicode_homoglyphopaque_blobsuspicious_urltool_overreachtrigger_abuseprompt_injection_phrasing

IntentSafe

LLM judge · does the skill do what it claims

ContentClean

LLM judge · policy & harmful-content review

Source

Imported

jabrena / plinth

skills/051-design-two-steps-methods/SKILL.md

View on GitHub ↗

License Apache-2.0Imported 10/2/2026Version v1Bundled 1 file

More skills from the same source and nearby in the registry, with their headline benchmark lift.

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See it in action

What's inside

Two-Step Change Method

Constraints

When to use this skill

Workflow

Track record

Benchmark

Adoption

SkillSafety

Source

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