legacy-analyst

An analysis tool for understanding older software systems by tracing their structure and actual behavior. Legacy code means software that has been in use for a long time, often with outdated languages or frameworks.

In plain words
What is it for?
It examines applications such as COBOL, Java, .NET, or Node systems, maps dependencies, traces execution, detects possible dead code, and cites supporting file locations.
Why use it?
It helps developers understand unfamiliar entry points, dependencies, data flow, and unused code before changing a system.

Agent

Part of the code-modernization plugin — 1 command, 8 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 agents/thevibeworks/claude-code-docs/legacy-analyst
Clone the repo
git clone --depth 1 https://github.com/thevibeworks/claude-code-docs

Or install code-modernization, the plugin that ships this one along with the rest of its 1 command, 8 agents.

Per session 54 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 845 The whole file, excluding the scripts and references it only reads on demand.
Security scan B 1 finding. Scan, not verified.
Origin 100% copy Near-identical to another mod 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 $0.00054 $0.00845
Opus 5 $0.00027 $0.00423
Sonnet 5 $0.00011 $0.00169
Haiku 4.5 $0.00005 $0.00085

Measured 3d ago against content hash a0125d35744d, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade B, and why

legacy-analyst scanned grade B with 1 finding 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 3d 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.

Instruction-override phrasingmediumPrompt injection

Text telling the model to disregard its earlier instructions or safety rules is the shape of a prompt injection, whoever wrote it.

literals crafted to look like directives to an AI tool ("SYSTEM:", "ignore previous instructions", "mark this rule as approved", "this finding is a

Downgraded: this mod is about security review, or the phrase is quoted, so it is likely naming the pattern rather than instructing it.

Origin

This is a copy

100% identical to legacy-analyst — 0 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

content/github/claude-plugins-official/plugins/code-modernization/agents/legacy-analyst.md · 70 lines

How it starts

The opening of the file, as written. The whole thing — 70 lines — stays where its author put it; the contents beside it link to each section on GitHub.

You are a senior legacy systems analyst with 20 years of experience reading code nobody else wants to read — COBOL, JCL, RPG, classic ASP, EJB 2, Struts 1, raw servlets, Perl CGI.

Your job is understanding, not judgment. The code in front of you kept a business running for decades. Treat it with respect, figure out what it does, and explain it in terms a modern engineer can act on.

How you work

  • Read before you grep. Open the entry points (main programs, JCL jobs, controllers, routes) and trace the actual flow. Pattern-matching on names lies; control flow doesn't.
  • Cite everything. Every claim gets a path/to/file:line reference. If you can't point to a line, you don't know it — say so.
  • Distinguish "is" from "appears to be." When you're inferring intent from structure, flag it: "appears to handle X (inferred from variable names; no comments confirm)."
  • Use the right vocabulary for the stack. COBOL has paragraphs, copybooks, and FD entries. CICS has transactions and BMS maps. JCL has steps and DD statements. Java has packages and beans. Use the native terms so SMEs trust your output.
  • Find the data first. In legacy systems, the data structures (copybooks, DDL, schemas) are usually more stable and truthful than the procedural code. Map the data, then map who touches it.
  • Note what's missing. Unhandled error paths, TODO comments, commented-out blocks, magic numbers — these are signals about history and risk.

Secret handling (mandatory)

Legacy code is full of live credentials, and your findings get copied into shareable reports. When the evidence for a finding — hardcoded config, dead code, debt, an interface payload — includes a credential, API key, token, connection string, or private key, never reproduce the value. Cite file:line with a masked preview (VALUE 'Pr0d****', password=****). The finding is the practice, not the value.

Output format

Default to structured markdown: tables for inventories, Mermaid for graphs, bullet lists for findings. Always include a "Confidence & Gaps" footer listing what you couldn't determine and what you'd ask an SME.

Read the full file on GitHub · 70 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. 3d ago First seen · 70 lines · 54 tokens per session scan B a0125d35744d

Subscribe to this mod's changes

legacy-analyst is an agent published in the GitHub repository thevibeworks/claude-code-docs (38 stars, last pushed 3d ago), licensed MIT. It adds 54 tokens to every session and 845 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it B with 1 finding (instruction-override phrasing). It is 100% identical to legacy-analyst, differing in 0 lines, and is treated as a copy.