simplifier

A method for simplifying a copied legacy system while keeping its structure and behavior. It uses characterization tests, which record and replay existing behavior, to check each change.

In plain words
What is it for?
Use it after the system has been moved to its target platform and its recorded behavior tests pass, working through one verified simplification at a time.
Why use it?
It removes unnecessary code or dependencies without relying on assumptions about what the old system does.

Skill for Claude CodeCodex

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 skills/adambien/airails/simplifier
Any agent
npx skills add AdamBien/airails --skill simplifier
Clone the repo
git clone --depth 1 https://github.com/AdamBien/airails

Made for: Claude Code, Codex.

Per session 146 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 837 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 $0.00146 $0.00837
Opus 5 $0.00073 $0.00418
Sonnet 5 $0.00029 $0.00167
Haiku 4.5 $0.00015 $0.00084

Measured 2d ago against content hash 484377132812, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

simplifier 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.

migrations/simplifier/SKILL.md · 52 lines

How it starts

The opening of the file, as written. The whole thing — 52 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Simplifier

The middle mode between rehost and rearchitect: the system keeps its structure, loses its noise. Every pass is semantics-preserving — and proven so, not assumed: the characterization suite is the green bar every pass must hold. This skill owns the pass discipline; what to transform and what replaces a dependency comes from the composed stack ecosystem.

Preconditions

  • The system runs on the target platform (1:1 lift completed).
  • Characterization recordings exist and replay green. No green bar, no simplification — run /characterization-tests first.

Pass Loop

  1. Pick one pass: a single transformation over a bounded scope, or a single dependency removal. Never batch.
  2. Apply it.
  3. Verify with the stack's own build/check loop, then replay the characterization suite.
  4. Green → commit the pass. Diff → reconcile (an accepted behavior change is a human decision, per characterization-tests) or revert the pass entirely.
  5. Log the pass in migration/SIMPLIFICATION.md — one line: date, pass, result.
  6. Repeat until the catalog finds no high-impact transformation and the dependency list is settled.

Code Passes

The transformation catalog and its impact-to-risk ordering come from the composed stack ecosystem:

  • Java — java-distiller: modern syntax, API upgrades, pattern adoption, dead-code removal.
  • Web frontend — web-conventions + web-components: semantic HTML, modern CSS over framework classes, custom elements over framework widgets, standards-based routing and state.

Constraint on top, any stack: preserve the public surface and the structure — packages, components, routes stay where they are. Internals may simplify, dead code may go; moves, splits, and merges are carving, and carving is /bc-carver + /sbce territory.

Dependency Passes

One dependency per pass. The ladder shape is stack-neutral — platform first, then copied source, then keep with justification; the rungs are the stack's:

Stack Ladder Manifest
Java Java SE → MicroProfile/Jakarta EE → copied source (zjson pattern) pom.xml
Web frontend Web platform, Baseline (fetch, querySelector, custom elements, modern CSS) → vendored source package.json, script tags

Read the full file on GitHub · 52 lines

Files

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.

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 · 52 lines · 0 tokens per session scan A 484377132812

Subscribe to this mod's changes

simplifier is a skill published in the GitHub repository AdamBien/airails (47 stars, last pushed 13d ago), licensed MIT. It adds 146 tokens to every session and 837 once invoked, about $0.0007 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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