--- title: "A blog article is not a product. No, Claude Code can’t understand COBOL applications." url: https://daily.dev/posts/a-blog-article-is-not-a-product-no-claude-code-can-t-understand-cobol-applications--aoszjtzrw source_url: https://swimm.io/blog/can-claude-understand-cobol type: article source: "Swimm" published: 2026-02-25T09:32:16.823Z updated: 2026-02-25T09:40:29.940Z tags: ["claude"] reading_time: 13 upvotes: 1 comments: 0 language: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # A blog article is not a product. No, Claude Code can’t understand COBOL applications. **[Swimm](https://daily.dev/sources/swimm)** · 13 min read · 1 upvotes · 0 comments ## Summary Swimm tested Claude Code (Opus 4.6) against its own deterministic platform on real CMS Medicare COBOL programs to evaluate business rule extraction quality. Results showed Claude covered only 24–35% of paragraphs on the larger program with up to 42% variance between identical runs, missed 27.5% of business rules entirely, dropped critical conditions (e.g., UNITS2 > 0), and hallucinated wrong regulatory dollar amounts. Swimm's deterministic static analysis achieved 100% coverage and accuracy on both programs. The post argues that LLM-based extraction is architecturally unsuited for mainframe modernization because it navigates code probabilistically rather than parsing the full AST, making it unreliable for regulated industries like healthcare and banking where every rule must be exact. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Similar posts on daily.dev - [Swimm 2.0: the understanding platform for AI modernization](https://daily.dev/posts/swimm-2-0-the-understanding-platform-for-ai-modernization-l5otr5ieu) · Swimm · 1 upvotes · 0 comments - [75% faster. 61% cheaper. What Swimm does for Claude Code.](https://daily.dev/posts/75-faster-61-cheaper-what-swimm-does-for-claude-code--r8eygsbeb) · Swimm · 0 upvotes · 0 comments --- Tags: [#claude](https://daily.dev/tags/claude) [View this post on daily.dev](https://daily.dev/posts/a-blog-article-is-not-a-product-no-claude-code-can-t-understand-cobol-applications--aoszjtzrw)