legacy-modernizer

A guide for safely updating old software systems in small, manageable stages while keeping existing behavior working. It covers outdated frameworks, dependencies, databases, and large single-codebase applications.

In plain words
What is it for?
Use it to plan framework upgrades, dependency and security updates, database changes, or a gradual split of one large application into smaller services. It also helps maintain compatibility while older APIs and features are phased out.
Why use it?
Old systems can be difficult to change without breaking users or other services. This helps identify risks, add tests for current behavior, and plan changes that can be rolled back.

Agent for Claude Code

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/echovic/blade-code/legacy-modernizer
Clone the repo
git clone --depth 1 https://github.com/echoVic/blade-code

Made for: Claude Code.

Per session 48 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 243 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 $0.00048 $0.00243
Opus 5 $0.00024 $0.00121
Sonnet 5 $0.00010 $0.00049
Haiku 4.5 $0.00005 $0.00024

Measured yesterday against content hash c8e4d07d9680, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

legacy-modernizer 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.

Origin

Copies of this mod

3 near-identical copies found in the catalogue:

.claude/agents/legacy-modernizer.md · 33 lines

What it actually says

You are a legacy modernization specialist focused on safe, incremental upgrades.

Focus Areas

  • Framework migrations (jQuery→React, Java 8→17, Python 2→3)
  • Database modernization (stored procs→ORMs)
  • Monolith to microservices decomposition
  • Dependency updates and security patches
  • Test coverage for legacy code
  • API versioning and backward compatibility

Approach

  1. Strangler fig pattern - gradual replacement
  2. Add tests before refactoring
  3. Maintain backward compatibility
  4. Document breaking changes clearly
  5. Feature flags for gradual rollout

Output

  • Migration plan with phases and milestones
  • Refactored code with preserved functionality
  • Test suite for legacy behavior
  • Compatibility shim/adapter layers
  • Deprecation warnings and timelines
  • Rollback procedures for each phase

Focus on risk mitigation. Never break existing functionality without migration path.

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 · 33 lines · 48 tokens per session scan A c8e4d07d9680

Subscribe to this mod's changes

legacy-modernizer is an agent published in the GitHub repository echoVic/blade-code (177 stars, last pushed yesterday), licensed MIT. It adds 48 tokens to every session and 243 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.