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Plain Claude Code drew AWS diagrams as well as official MCP servers once the prompt was tuned
Plain Claude Code, with no MCP server or skill, matched AWS's and draw.io's official diagram tools in a five-setup test published on dev.to. Every setup improved as the author kept adding instructions, and the finding covers one architecture on Claude Opus 5, graded by the author.
The Engineer · Build desk
What happened
- AWS deprecated its Diagram MCP Server in March 2026 and has since yanked every PyPI release; that deprecation is why the author started testing.
- On a first prompt that only described the architecture, none of the five setups produced a diagram usable without edits, and each failed in a different way.
- AWS's own diagram skill added numbered badges and a data-flow panel that were never requested, and drew a box around every service icon.
- Plain Claude Code's first diagram was fairly tidy, but it colored S3 orange and printed service names in two places.
Compiled by The EngineerSomething wrong?How this is made
Why it matters
- constraint A PNG-only tool cannot meet the author's editability criterion at any prompt quality, so the deprecated AWS server was capped on one of six criteria before its first run.
- decision Teams moving off the deprecated server can trial a written prompt in a plain session against AWS's replacement skill before adopting the skill, since AWS claims only parity for it.
- exposure A comparison of Claude Code add-ons run without --strict-mcp-config also measures the connectors on the tester's claude.ai account, so its supposedly plain baseline is contaminated.
The test harness is careful work. Every session started from `claude --setting-sources project --strict-mcp-config`, adding `--mcp-config mcp.json` for the two MCP servers or `--plugin-dir` for the AWS skill and the draw.io plugin [11]. The strict flag exists for a reason the author ran into. Without it, MCP connectors set up in claude.ai still appear inside the Claude Code session; for the author, that was an AWS documentation search connector [12]. `--safe-mode` turns off CLAUDE.md, skills, plugins and MCP servers in one move. The author tried it and dropped it, because it also turned off the plugins being compared [13].
The author graded on six criteria: reproducibility, cost in tokens and time, faithfulness to the request, readability, a look without AI-style decoration, and editability, meaning a .drawio file [10]. Setups 2 to 5 were asked for draw.io XML. The AWS Diagram MCP Server outputs only PNG, so its prompt ended with a request for a PNG instead [9].
The architecture was a two-AZ web stack. CloudFront fronted an ALB targeting an ECS Fargate service in both AZs, with an Aurora MySQL writer and reader in different AZs [14]. S3 held static files behind CloudFront, CloudWatch collected logs and metrics, and each public subnet had a NAT Gateway [14]. On the first pass the Diagram MCP Server returned a tangled diagram with rounded icons [16]. The draw.io MCP server and plugin came closer, but both ran lines over text. The server added notes nobody requested, and the plugin rounded the corners of its lines [18].
Every first-round fault the author listed was cosmetic or an addition nobody asked for [15]. I think a written instruction can forbid each one. The author's method was to add such an instruction whenever something looked off [1], and by the end every setup had improved a lot [2].
The result transfers only as far as the conditions match. The runs used Claude Code 2.1.278 with Claude Opus 5 in September 2026 [4]. The prompts were written in Japanese and translated for the post [5]. The final prompt was refined against one architecture and the five sets of failures it produced. A team with a larger or different stack would be testing instructions fitted to someone else's diagram. The first-round faults are documented setup by setup. The verdict that plain Claude Code did as well as any of the others is the author's, against criteria the author chose [3].
AWS set a modest bar for its own replacement. The deprecation notice says the diagram skill in the deploy-on-aws plugin "generates equivalent diagrams directly through Claude Code without requiring a running MCP server" [7]. "Equivalent, not better," the author wrote [8].
What to watch
- A rerun of the author's final prompt on a larger or different AWS architecture, or on a later Claude model, would show whether plain-session parity holds outside this one two-AZ stack.
- Changes to the deploy-on-aws diagram skill that go past the 'equivalent' output AWS's deprecation notice promises would reopen the case for the tool over the prompt.