What is costco-mcp CLAUDE.md?

Instructions for a server that connects to Costco’s internal online services through their GraphQL interface. It uses browser-based sign-in and saved refresh tokens to access receipts, orders, and product information without scraping pages at runtime.

Use it when changing the Costco server, its GraphQL client, browser login flow, account token storage, product cache, or MCP tools.

It documents the system’s architecture and authentication rules so agents can work on account handling and API access safely.

How thehesiod/costco-mcp configures Claude Code

Reuse

Borrowing it

Nothing to install: this file belongs to thehesiod/costco-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/thehesiod/costco-mcp/main/CLAUDE.md

Clone the repo

git clone --depth 1 https://github.com/thehesiod/costco-mcp

Made for: Claude Code.

Wrote this? Show the measurements

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README.md

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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/thehesiod/costco-mcp/claude-md"><img src="https://agentmods.dev/badge/instructions/thehesiod/costco-mcp/claude-md.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 2,043 This file is loaded in full into every session.

When invoked 2,043 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.

Model	Per session	Once invoked
Fable 5.1	$0.02043	$0.02043
Opus 5	$0.01022	$0.01022
Sonnet 5	$0.00409	$0.00409
Haiku 4.5	$0.00204	$0.00204

Measured 9d ago against content hash e3c76402f76d, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-09, from the pricing page.

Security

Grade A, and why

costco-mcp CLAUDE.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 9d 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.

CLAUDE.md · 146 lines

How it starts

The opening of the file, as written. The whole thing — 146 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Costco MCP Server

Architecture

MCP server that talks directly to Costco's internal GraphQL API using OAuth2 refresh tokens extracted from a browser session. No scraping, no headless browser at runtime — all API calls are pure HTTP via httpx[http2]. Runs as stdio transport.

src/costco_mcp_server/
  server.py         — MCP tool definitions (FastMCP)
  api.py            — CostcoAPI: GraphQL client, receipt/order/product queries
  auth.py           — CostcoAuth: per-account refresh token persistence + bearer minting
  auth_browser.py   — costco-auth-browser console script (launches Chrome with remote debugging)
  product_cache.py  — SQLite cache for product names + department codes

Key Patterns

Authentication (Azure AD B2C)

Costco's SPA uses Azure AD B2C OAuth2. Tenant + policy + client IDs are public (ship in Costco's own browser JS) and hardcoded in auth.py.
Refresh tokens live in ~/.costco-mcp/accounts/<name>/auth.json. Valid ~90 days.
Bearer tokens (id_token) are minted on demand, cached in memory with a 120-second expiry buffer (_is_token_expired).
No ROPC (resource owner password credentials) — initial auth requires a browser login to Costco's MFA flow. After that, it's pure API via the refresh token.
client-identifier header (api.py:CLIENT_IDENTIFIER) must be the exact value 481b1aec-aa3b-454b-b81b-48187e28f205. Random UUIDs cause 401. This appears to be a static per-app identifier (not per-user), copied from Costco's browser bundle.

Multi-account

Accounts: ~/.costco-mcp/accounts/<name>/auth.json per account. Config (default account + account list) at ~/.costco-mcp/config.json.
Every MCP tool takes an optional account parameter. Omitting it uses the default.
Legacy single-account ~/.costco-mcp/auth.json is auto-migrated to default/ on first load (_migrate_legacy).
_apis dict in server.py caches CostcoAPI instances per account name. save_refresh_token evicts on token update.

Read the full file on GitHub · 146 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.

9d ago First seen · 146 lines · 2,043 tokens per session scan A e3c76402f76d

Subscribe to this mod's changes

costco-mcp CLAUDE.md is an instructions file published in the GitHub repository thehesiod/costco-mcp (2 stars, last pushed 4mo ago), licensed MIT. It adds 2,043 tokens to every session, about $0.0102 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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costco-mcp: Instructions file for Claude Code