What is fast-mcp-scala CLAUDE.md?

Project instructions for fast-mcp-scala, a Scala 3 library for building MCP servers. They cover its typed and annotation-based APIs, Mill build commands, and tests for JVM and Scala.js.

Use them when adding MCP tools, resources, or prompts, changing shared JVM and Scala.js code, or running compilation, tests, and formatting checks.

They help agents use the correct Scala, build, formatting, and cross-platform conventions.

How TJC-LP/fast-mcp-scala configures Claude Code

Reuse

Borrowing it

Nothing to install: this file belongs to TJC-LP/fast-mcp-scala. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file

curl -O https://raw.githubusercontent.com/TJC-LP/fast-mcp-scala/main/CLAUDE.md

Clone the repo

git clone --depth 1 https://github.com/TJC-LP/fast-mcp-scala

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.

README.md

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Your own site

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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.

Your own site · 80×15

<a href="https://agentmods.dev/instructions/tjc-lp/fast-mcp-scala/claude-md"><img src="https://agentmods.dev/badge/instructions/tjc-lp/fast-mcp-scala/claude-md.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 6,496 This file is loaded in full into every session.

When invoked 6,496 The same file — it is already loaded in full.

Security scan C 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.

Model	Per session	Once invoked
Fable 5.1	$0.06496	$0.06496
Opus 5	$0.03248	$0.03248
Sonnet 5	$0.01299	$0.01299
Haiku 4.5	$0.00650	$0.00650

Measured 2d ago against content hash c933e5277942, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-10, from the pricing page.

Security

Grade C, and why

fast-mcp-scala CLAUDE.md scanned grade C 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 2d 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.

Recursive force deletehighDestructive command

rm -rf with a variable or a broad path is one typo away from removing the wrong tree.

rm -rf out/fast-mcp-scala && ./mill fast-mcp-scala.compile

CLAUDE.md · 365 lines

How it starts

The opening of the file, as written. The whole thing — 365 lines — stays where its author put it; the contents beside it link to each section on GitHub.

CLAUDE.md - fast-mcp-scala Development Guide

Project Overview

fast-mcp-scala is a high-level Scala 3 library for building Model Context Protocol (MCP) servers. It provides two registration paths:

Annotation-driven (@Tool, @Resource, @Prompt + scanAnnotations) — zero-boilerplate on JVM, Scala.js/Bun, and Scala Native
Typed contracts (McpTool, McpPrompt, McpStaticResource, McpTemplateResource) — explicit, first-class values, all three platforms

Both paths converge on the same McpServer trait and support @Param metadata on parameters/fields.

Three platforms: JVM (stdio + HTTP), Scala.js/Bun (stdio + HTTP), and Scala Native (stdio only, EXPERIMENTAL — published as fast-mcp-scala_native0.5_3; zio-http has no Native artifacts, so McpServerApp[Http] fails to compile there by design).

Build System

Build tool: Mill 1.1.8 (configured in .mill-version) Scala: 3.9.0 (LTS) Plugins: mill-bun-plugin 0.3.1 (Scala.js + Bun integration; explicit scalaJSVersion, managed Bun 1.4.1, frozen js/bun.lock)

Common Commands

# Aggregates (JVM + Scala.js + Scala Native)
./mill fast-mcp-scala.compile                       # Compile all platforms
./mill fast-mcp-scala.test                          # All tests, all three platforms
./mill fast-mcp-scala.reformat                      # Auto-format every Scala source
./mill fast-mcp-scala.checkFormat                   # Scalafmt check (CI uses this)

# Single-platform
./mill fast-mcp-scala.jvm.test                      # JVM tests only
./mill fast-mcp-scala.js.test                       # Scala.js conformance tests only (Bun)
./mill fast-mcp-scala.js.bunLock                    # Regenerate js/bun.lock after changing bunDevDeps
./mill fast-mcp-scala.scalaNative.test              # Scala Native tests (links a native binary)
./mill fast-mcp-scala.scalaNative.nativeLink        # Standalone LLVM binary of AnnotatedServer
./mill fast-mcp-scala.jvm.test.testOnly com.tjclp.fastmcp.macros.ToolProcessorTest   # class selectors go through testOnly

# Publish
./mill fast-mcp-scala.jvm.publishLocal              # Publish JVM artifact to ~/.ivy2/local
./mill fast-mcp-scala.js.publishLocal               # Publish Scala.js artifact to ~/.ivy2/local
./mill -i __.publishLocal                           # Publish all three artifacts

Read the full file on GitHub · 365 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.

2d ago Changed · +19 lines · +668 tokens per session c933e5277942
3d ago Changed · +19 lines · +1,201 tokens per session d8b38140c266
5d ago Changed · +1 lines · +96 tokens per session 2d86e4911f93
6d ago Changed · +11 lines · +423 tokens per session 1f92df906159
11d ago First seen · 315 lines · 4,108 tokens per session scan C 43379860ded7

Subscribe to this mod's changes

fast-mcp-scala CLAUDE.md is an instructions file published in the GitHub repository TJC-LP/fast-mcp-scala (24 stars, last pushed yesterday), licensed MIT. It adds 6,496 tokens to every session, about $0.0325 per session on Opus 5. A static security scan graded it C with 1 finding (recursive force delete). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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Working notes and architecture documentation for the new esbuild-based build system in build/next. Use when making changes to the new build pipeline (transpile/bundle commands, NLS plugin, source-map handling, resource copying, or self-hosting watch tasks).

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fast-mcp-scala: Instructions file for Claude Code