foundry-implementation

A set of implementation rules for Rust command-line programs, including a standard sequence for validation, operations, responses, and errors.

In plain words
What is it for?
It guides async command handlers, early validation, serialized response fields, and contextual filesystem errors.
Why use it?
It gives commands a consistent structure and adds useful context when an operation fails.

Cursor rule for Cursor

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.

agentmods
npx agentmods add rules/cafreeman/foundry-mcp/foundry-implementation
Clone the repo
git clone --depth 1 https://github.com/cafreeman/foundry-mcp

Made for: Cursor.

Per session 0 Nothing until a file matches its globs; then the whole rule loads.
When invoked 967 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
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 $0.00000 $0.00967
Opus 5 $0.00000 $0.00483
Sonnet 5 $0.00000 $0.00193
Haiku 4.5 $0.00000 $0.00097

Measured yesterday against content hash 2f67b2cf0c5d, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

foundry-implementation 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.

.cursor/rules/foundry-implementation.mdc · 154 lines

How it starts

The opening of the file, as written. The whole thing — 154 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Foundry Implementation Patterns

CLI Command Structure

Standard Pattern

// All commands: async fn execute(args: XxxArgs) -> Result<XxxResponse>
pub async fn execute(args: CreateProjectArgs) -> Result<CreateProjectResponse> {
    validate_args(&args).context("Invalid arguments")?;
    let result = perform_operation(&args).context("Operation failed")?;
    Ok(build_response(result))
}

Response Format (REQUIRED)

#[derive(Serialize, Debug)]
pub struct CommandResponse {
    // Core data (project, spec, etc.)
    pub next_steps: Vec<String>,        // REQUIRED: Workflow guidance
    pub validation_status: String,      // REQUIRED: "complete", "partial", "failed"

    #[serde(skip_serializing_if = "Option::is_none")]
    pub workflow_hints: Option<Vec<String>>,  // OPTIONAL: LLM guidance
}

Error Handling

Context Pattern

use anyhow::{Context, Result};

// Add meaningful context to all operations
std::fs::create_dir_all(&project_dir)
    .context(format!("Failed to create project directory: {}", project_dir.display()))?;

// Validate early, fail fast
validate_project_name(&args.project_name)
    .context("Invalid project name format")?;

Validation Functions

pub fn validate_project_name(name: &str) -> Result<()> {
    if name.is_empty() || !name.chars().all(|c| c.is_alphanumeric() || c == '-' || c == '_') {
        anyhow::bail!("Project name must use kebab-case (alphanumeric and hyphens only)");
    }
    Ok(())
}

User Memory Compliance

Function Returns (Memory #7066344)

  • ONLY return what's needed - avoid unused return values
  • Use #[serde(skip_serializing_if = "Option::is_none")] for optional fields
  • Focus responses on immediate workflow needs

Content Creation (Memory #7065075)

  • NEVER implement automatic content generation or summarization
  • ALWAYS require LLMs to provide complete content as arguments
  • CLI validates format and length, but NOT content quality
// ✅ Good: LLM provides content
pub struct CreateProjectArgs {
    pub project_name: String,
    pub vision: String,      // LLM-provided content
    pub tech_stack: String,  // LLM-provided content
}

// ❌ Bad: CLI generates content
pub fn generate_summary_from_vision(vision: &str) -> String {
    // Never implement this
}

Read the full file on GitHub · 154 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 First seen · 154 lines · 0 tokens per session scan A 2f67b2cf0c5d

Subscribe to this mod's changes

foundry-implementation is a cursor rule published in the GitHub repository cafreeman/foundry-mcp (4 stars, last pushed 5mo ago), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 967 tokens. 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 2026-08-31.