ynab-budget-mcp: Instructions file for Codex

AGENTS.md

ynab-budget-mcp AGENTS.md is an instructions file for Codex, OpenCode from Orlando-Villanueva/ynab-budget-mcp. It costs 560 tokens per session, scanned A, original, MIT.

A set of AGENTS.md instructions for developing the YNAB MCP server, including its purpose, files, setup, commands, and environment configuration.

In plain words
What is it for?
Use it when modifying the YNAB server, especially its TypeScript source, YNAB client, MCP protocol code, or tests.
Why use it?
It gives coding agents project-specific guidance so they know how the repository is organised and how to start and test it.

Instructions file for CodexOpenCode

Written for Codex and OpenCode: the file is AGENTS.md. Also seen: mentions AGENTS.md.

This is Orlando-Villanueva/ynab-budget-mcp's own configuration. It tells Codex and OpenCode how to work on ynab-budget-mcp itself, so it is not a mod to install elsewhere. Copy it as a starting point and replace the rules that are about this project. Everything ynab-budget-mcp configures →

Reuse

Borrowing it

Nothing to install: this file belongs to Orlando-Villanueva/ynab-budget-mcp. 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/Orlando-Villanueva/ynab-budget-mcp/main/AGENTS.md
Clone the repo
git clone --depth 1 https://github.com/Orlando-Villanueva/ynab-budget-mcp

Made for: Codex, OpenCode.

Wrote this? Show the measurements

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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.

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Per session 560 This file is loaded in full into every session.
When invoked 560 The same file — it is already loaded in full.
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 $0.00560 $0.00560
Opus 5 $0.00280 $0.00280
Sonnet 5 $0.00112 $0.00112
Haiku 4.5 $0.00056 $0.00056

Measured 11d ago against content hash 237b496c17a2, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-11, from the pricing page.

Security

Grade A, and why

ynab-budget-mcp AGENTS.md 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 11d 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.

AGENTS.md · 59 lines

How it starts

The opening of the file, as written. The whole thing — 59 lines — stays where its author put it; the contents beside it link to each section on GitHub.

AGENTS.md

Purpose

This repository contains a local MCP server for YNAB. It lets MCP-capable agents query budgeting data through curated tools instead of raw shell commands.

Project Shape

  • Runtime: Node.js 22.9+
  • Language: TypeScript executed directly with Node's --experimental-transform-types
  • Package manager: npm
  • Test runner: node:test
  • Dependencies: intentionally minimal; prefer built-in Node features unless a dependency is clearly justified

Core Files

  • README.md: setup, usage, MCP client configuration, and smoke-test instructions
  • src/index.ts: process entrypoint that constructs the client, registers tools, and starts the stdio server
  • src/mcp.ts: lightweight MCP/JSON-RPC server implementation over stdio
  • src/tools.ts: public ynab_* tool definitions, input validation, summaries, and error wrapping
  • src/ynab/client.ts: YNAB API client, auth, query building, delta caching, and error mapping
  • src/ynab/normalize.ts: milliunit-to-currency normalization helpers
  • test/*.test.ts: protocol, client, and tool behavior tests

Commands

  • Start server: npm run start
  • Run tests: npm test

Environment

  • Required env var: YNAB_ACCESS_TOKEN
  • Keep secrets in .env or local environment variables
  • Never hardcode tokens or include them in test fixtures, prompts, logs, or committed files

Implementation Rules

  • Keep the tool surface curated and read-only by default; guarded assignment preview/apply is the sole experimental opt-in write workflow
  • Do not add generic raw endpoint passthrough tools unless explicitly requested
  • Prefer /v1/plans endpoints over legacy /budgets paths
  • Preserve raw milliunit values and add normalized *_currency fields where helpful
  • Keep caching in-memory only unless persistent caching is explicitly requested
  • Use clear structured errors for auth failures, rate limits, not founds, and upstream failures

Editing Guidance

  • Prefer small, focused changes
  • Maintain the current layered structure: MCP transport, tool layer, YNAB client, normalization helpers
  • Add or update tests with behavior changes
  • Prefer built-in Node APIs over pulling in new packages
  • Avoid writing to stdout outside MCP protocol responses; use stderr for diagnostics

Read the full file on GitHub · 59 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. 11d ago First seen · 59 lines · 560 tokens per session scan A 237b496c17a2

Subscribe to this mod's changes

ynab-budget-mcp AGENTS.md is an instructions file published in the GitHub repository Orlando-Villanueva/ynab-budget-mcp (0 stars, last pushed 20d ago), licensed MIT. It adds 560 tokens to every session, about $0.0028 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 2026-08-31.

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