cheatsheet-errors

cheatsheet-errors is a skill for Claude Code from mendixlabs/mxcli. It costs 52 tokens per session (2,620 once invoked), scanned A, original, Apache-2.0.

A quick reference for fixing common MDL syntax errors. MDL is the language used by Mendix for describing and checking application logic.

In plain words
What is it for?
It covers undeclared variables, invalid data retrieval sources, list operations, and expression mistakes.
Why use it?
It helps developers move from an error reported by mxcli, the Mendix command-line checker, to a likely correction without searching the full reference.

Skill for Claude Code

Written for Claude Code: installed under .claude/.

Good fit It covers undeclared variables, invalid data retrieval sources, list operations, and expression mistakes.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/mendixlabs/mxcli/cheatsheet-errors
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.

Any agent
npx skills add mendixlabs/mxcli --skill cheatsheet-errors
Clone the repo
git clone --depth 1 https://github.com/mendixlabs/mxcli

Made for: Claude Code.

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 cheatsheet-errors

README.md
[![agentmods](https://agentmods.dev/badge/skills/mendixlabs/mxcli/cheatsheet-errors/github.svg)](https://agentmods.dev/skills/mendixlabs/mxcli/cheatsheet-errors)
Your own site
<a href="https://agentmods.dev/skills/mendixlabs/mxcli/cheatsheet-errors"><img src="https://agentmods.dev/badge/skills/mendixlabs/mxcli/cheatsheet-errors/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for cheatsheet-errors

Your own site · 80×15
<a href="https://agentmods.dev/skills/mendixlabs/mxcli/cheatsheet-errors"><img src="https://agentmods.dev/badge/skills/mendixlabs/mxcli/cheatsheet-errors.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 52 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,620 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe. Third-party audits
  • NVIDIA SkillSpector pass 7 Sept 2026
How audits are shown
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 $0.00052 $0.02620
Opus 5.5 $0.00021 $0.01048
Sonnet 5.5 $0.00010 $0.00524
Haiku 4.5 $0.00005 $0.00262

Measured yesterday against content hash 266df640eb4d, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

cheatsheet-errors 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.

.claude/skills/mendix/cheatsheet-errors/SKILL.md · 310 lines

How it starts

The opening of the file, as written. The whole thing — 310 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Find it fast

sed -n '<from>,<to>p' SKILL.md one section rather than reading the file; ./mxcli syntax <topic> answers how do I write this for a fraction of either.

lines section
26-78 Variable Errors
79-130 Expression Errors
131-178 Control Flow Errors
179-216 Syntax Errors
217-281 Reference Errors
282-297 Studio Pro Error Code Reference
298-309 Quick Validation Checklist

MDL Common Errors Cheatsheet

Quick fixes for common MDL syntax errors.

Variable Errors

"Variable 'X' is not declared"

Problem: Using SET on a variable that wasn't declared.

-- WRONG
if $value > 10 then
  set $IsValid = false;  -- ERROR: $IsValid not declared
end if;

Fix: Add DECLARE before SET.

-- CORRECT
declare $IsValid boolean = true;
if $value > 10 then
  set $IsValid = false;
end if;

"Selected type is not allowed" (CE0053)

Problem: Declaring an object (entity) or list variable. A declare maps to a Create Variable activity, which only accepts primitives (String/Integer/Long/Decimal/Boolean/DateTime/Enumeration). Declaring an object or list is rejected (CE0053/CE0038, plus CE7247 on any later set) — bare or initialized. The as keyword is also a parse error in mxcli. mxcli check flags an object declare as MDL043 and a list declare as MDL040.

-- WRONG: declaring an object — there is no "empty object variable" (MDL043)
declare $Product Module.Product = empty;
declare $Product as Module.Product;         -- AS is also a parse error
-- WRONG: declaring a list (MDL040)
declare $Products list of Module.Product = empty;

Fix: Objects and lists can't be declared — get them from a source that produces one.

-- object: a microflow parameter, a retrieve, a create, or a loop iterator
retrieve $Product from Module.Product where Code = $Code first;  -- retrieve
$Product = create Module.Product (Name = $Name);                   -- create
-- or: create microflow M.Save ($Product: Module.Product) ... / loop $Product in $Products ...

-- list: a parameter, a retrieve, or a create list
$Products = create list of Module.Product;   -- empty list to accumulate into
retrieve $Products from Module.Product where ...;  -- or populate from the database

Read the full file on GitHub · 310 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. yesterday Changed · +6 lines 266df640eb4d
  2. 5d ago Changed · +16 lines 70f319488fab
  3. 8d ago Changed · +1 lines 098e95219929
  4. 15d ago Changed 5e81fe42d282
  5. 1mo ago Changed · +2 lines fac7d09863ad
  6. 1mo ago First seen · 285 lines · 52 tokens per session scan A 0fd51e2baccf

Subscribe to this mod's changes

cheatsheet-errors is a skill published in the GitHub repository mendixlabs/mxcli (130 stars, last pushed yesterday), licensed Apache-2.0. It adds 52 tokens to every session and 2,620 once invoked, about $0.0002 per session on Opus 5.5. 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.

Related

Other skills, from other repositories

codegraph

Analyze indexed codebases via graph database (neug) and vector index (zvec). Covers call graphs, dependencies, dead code, hotspots, module coupling, architecture reports, semantic search, impact analysis, bug root cause from GitHub issues, class diagrams (UML), and PR review (risk scoring, conflict detection…

QwenLM/qwen-code · 0 tokens

stuck

Diagnose frozen, stuck, or slow Qwen Code sessions on this machine. Scans for problematic processes, high CPU/memory usage, hung subprocesses, and debug logs. Use /stuck or /stuck to focus on a specific process.

QwenLM/qwen-code · 57 tokens

structured-debugging

Hypothesis-driven debugging methodology for hard bugs. Use this skill whenever you're investigating non-trivial bugs, unexpected behavior, flaky tests, or tracing issues through complex systems. Activate proactively when debugging requires more than a quick glance — especially when the first attempt at a fix didn't…

QwenLM/qwen-code · 85 tokens

memory-leak-debug

Diagnose memory leaks in the Qwen Code CLI using heap snapshots and the chrome-devtools CLI. Use when investigating high memory usage, unbounded growth, or suspected object retention issues.

QwenLM/qwen-code · 42 tokens

bugfix

Fix a bug from a GitHub issue, following the reproduce-first workflow. Use when the user asks to fix a bug, investigate a GitHub issue, or debug a user-reported problem. Takes a GitHub issue URL or number as input.

QwenLM/qwen-code · 53 tokens

test-failure-explorer

Import and query an existing Vitest 3.2 JSON report to explore test failures, file-level errors and original diagnostic evidence.

QwenLM/qwen-code · 32 tokens