langium

langium is a skill for Claude Code from eclipse-langium/langium-ai. It costs 33 tokens per session (9,757 once invoked), scanned A, original, MIT.

A reference guide to Langium, a framework for building custom programming languages and related editor tools with TypeScript. It explains how language files are read, understood, checked, and connected to editor features.

In plain words
What is it for?
Use it to understand language grammar, generated code, parsing, name resolution, validation, project workspaces, and editor support.
Why use it?
It gives agents and developers a map of the parts involved when they need to navigate, debug, or extend a Langium project.

Skill for Claude Code

Written for Claude Code: user-invocable in frontmatter.

Good fit Use it to understand language grammar, generated code, parsing, name resolution, validation…

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Install with agentmods
npx agentmods add skills/eclipse-langium/langium-ai/langium
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 eclipse-langium/langium-ai --skill langium
Clone the repo
git clone --depth 1 https://github.com/eclipse-langium/langium-ai

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 langium

README.md
[![agentmods](https://agentmods.dev/badge/skills/eclipse-langium/langium-ai/langium.svg)](https://agentmods.dev/skills/eclipse-langium/langium-ai/langium)
Your own site
<a href="https://agentmods.dev/skills/eclipse-langium/langium-ai/langium"><img src="https://agentmods.dev/badge/skills/eclipse-langium/langium-ai/langium.svg" alt="Measured on agentmods" height="20"></a>
Per session 33 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 9,757 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.
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 $0.00033 $0.09757
Opus 5 $0.00016 $0.04879
Sonnet 5 $0.00007 $0.01951
Haiku 4.5 $0.00003 $0.00976

Measured 7d ago against content hash 3973f4c92656, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-06, from the pricing page.

Security

Grade A, and why

langium 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 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.

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.

skills/langium/SKILL.md · 1,089 lines

How it starts

The opening of the file, as written. The whole thing — 1,089 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Langium SKILL.md

A comprehensive guide to understanding how Langium-based projects work — from grammar definition through code generation, runtime parsing, linking, validation, and LSP integration. Reading this document should make an agent fully proficient at navigating, debugging, and extending any Langium DSL project.


Table of Contents

  1. High-Level Architecture
  2. The Grammar Language
  3. Code Generation (Build Time)
  4. Dependency Injection System
  5. Lexing
  6. Parsing: Tokens → CST → AST
  7. The Document Lifecycle (DocumentState Pipeline)
  8. Scope Computation
  9. Scope Provider and Name Resolution
  10. Linking and Cross-Reference Resolution
  11. Validation
  12. Workspace Management
  13. LSP Integration
  14. Common Customization Patterns
  15. End-to-End Runtime Flow

1. High-Level Architecture

Langium is a language engineering framework that takes a .langium grammar file and produces a fully operational TypeScript-based DSL toolkit with LSP support. The architecture has two major phases:

Build timelangium-cli reads .langium grammars and generates:

  • ast.ts — TypeScript interfaces for every AST node, type guards, and an AstReflection class
  • grammar.ts — The grammar serialized as JSON, lazy-loaded at runtime
  • module.ts — A DI module providing Grammar, LanguageMetaData, and AstReflection services

Runtime — A service-oriented architecture driven by dependency injection:

  • All components (parser, lexer, linker, scope provider, validator, LSP handlers) are registered as services
  • Two service layers: shared services (cross-language: workspace, index, document management) and language-specific services (parser, references, validation — one set per language)
  • Users customize behavior by providing partial DI modules that override default service factories

Read the full file on GitHub · 1,089 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 · 1,089 lines · 33 tokens per session scan A 3973f4c92656

Subscribe to this mod's changes

langium is a skill published in the GitHub repository eclipse-langium/langium-ai (30 stars, last pushed 10d ago), licensed MIT. It adds 33 tokens to every session and 9,757 once invoked, about $0.0002 per session on Opus 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.

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