legacy-analyst

legacy-analyst is an agent for Claude Code from anthropics/claude-plugins-official. It costs 54 tokens per session (845 once invoked), scanned B, original, Apache-2.0.

A detailed investigation of an old codebase that explains its structure, data, dependencies, and actual behavior. It can analyze technologies ranging from COBOL and JCL to Java, .NET, and Node.

In plain words
What is it for?
It maps dependencies, identifies entry points and dead code, follows data and control flow, and answers what a legacy system really does.
Why use it?
It replaces guesses based on names or documentation with conclusions traced to the code and its execution flow.

Agent for Claude Code ✓ vendor

Written for Claude Code: shipped in a Claude Code plugin.

Part of the code-modernization plugin — 10 commands, 8 agents shipped together

Good fit It maps dependencies, identifies entry points and dead code, follows data and control flow, and answers what a legacy system really does.

Compare 6 agents from other repositories ↓
Install with agentmods
npx agentmods add agents/anthropics/claude-plugins-official/legacy-analyst
About the project

Claude Code Plugins Directory is a marketplace containing plugins for Claude Code, including tools, commands, skills, agents, hooks, and model context servers. Claude Code users browse it to install Anthropic-maintained or approved third-party extensions.

anthropics/claude-plugins-official · 35,987 stars · on GitHub · code.claude.com

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.

Clone the repo
git clone --depth 1 https://github.com/anthropics/claude-plugins-official

Made for: Claude Code.

Or install code-modernization, the plugin that ships this one along with the rest of its 10 commands, 8 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 legacy-analyst

README.md
[![agentmods](https://agentmods.dev/badge/agents/anthropics/claude-plugins-official/legacy-analyst.svg)](https://agentmods.dev/agents/anthropics/claude-plugins-official/legacy-analyst)
Your own site
<a href="https://agentmods.dev/agents/anthropics/claude-plugins-official/legacy-analyst"><img src="https://agentmods.dev/badge/agents/anthropics/claude-plugins-official/legacy-analyst.svg" alt="Measured on agentmods" height="20"></a>
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. A grade says what 26 rules found in the file — not that it is safe.
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 $0.00054 $0.00845
Opus 5 $0.00027 $0.00423
Sonnet 5 $0.00011 $0.00169
Haiku 4.5 $0.00005 $0.00085

Measured 7d ago against content hash a0125d35744d, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-07, 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 7d 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

Copies of this mod

1 near-identical copy found in the catalogue:

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. 7d 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 anthropics/claude-plugins-official (35,987 stars, last pushed yesterday), licensed Apache-2.0. 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). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.