sncro-relay: Instructions file for Claude Code

CLAUDE.md

sncro-relay CLAUDE.md is an instructions file for Claude Code from scottconfusedgorilla/sncro-relay. It costs 635 tokens per session, scanned A, original, MIT.

A repository guide for sncro-relay, an open-source service that connects browser-side agents and application framework plugins through a relay. It documents the folders, Python technologies, local setup, tests, and demo app.

In plain words
What is it for?
It is for running the relay and demo locally, understanding the FastAPI and Flask components, and running the pytest test suite.
Why use it?
It gives an agent the project context needed to work in the repository without first rediscovering its structure and development commands.

Instructions file for Claude Code

Written for Claude Code: the file is CLAUDE.md.

This is scottconfusedgorilla/sncro-relay's own configuration. It tells Claude Code how to work on sncro-relay 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 sncro-relay configures →

Reuse

Borrowing it

Nothing to install: this file belongs to scottconfusedgorilla/sncro-relay. 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/scottconfusedgorilla/sncro-relay/master/CLAUDE.md
Clone the repo
git clone --depth 1 https://github.com/scottconfusedgorilla/sncro-relay

Made for: Claude Code.

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Per session 635 This file is loaded in full into every session.
When invoked 635 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 $0.00635 $0.00635
Opus 5 $0.00318 $0.00318
Sonnet 5 $0.00127 $0.00127
Haiku 4.5 $0.00064 $0.00064

Measured 9d ago against content hash 14540a4e8790, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-09, from the pricing page.

Security

Grade A, and why

sncro-relay 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 · 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.

sncro-relay

This is the open-source half of sncro. It contains the MCP relay, the browser-side agent, and the framework plugins.

Repo layout

  • relay/ — FastAPI app. Mounts an MCP server at /tools/mcp, exposes long-poll endpoints for agent.js under /session/{key}/*, serves agent.js from /static/.
  • middleware/ — framework plugins that customers install into their apps. sncro_middleware.py (FastAPI) and sncro_flask.py (Flask).
  • trysncro/try.sncro.net, a deliberately-broken demo app used for end-to-end testing.
  • tests/ — pytest suite. 44 tests covering the relay, both plugins, and end-to-end flows.

The dashboard, auth, admin, billing, and landing page live in a separate private repo.

Tech stack

  • Python 3.11+, FastAPI, Starlette
  • MCP server via the mcp Python SDK
  • Flask (for the Flask plugin and its tests)
  • slowapi for rate limiting
  • pytest for tests

Running locally

pip install -r requirements.txt
pytest                          # 44 tests should pass
uvicorn relay.main:app --reload # run the relay on localhost:8000

Running the demo

pip install -r trysncro/requirements.txt
DEBUG=true uvicorn trysncro.app:app --port 8001
# Browse to http://localhost:8001

Testing

pytest at the repo root. The suite is fast (< 5s). No integration tests that hit real services.

Commit style

Commits that deploy a new relay build are prefixed with the build number, e.g. (build 093) Advertise tools/listChanged on the MCP server. Security-related work is labeled with a phase letter (A through I so far). See git log --oneline for the shape.

Security

Every Critical/High from the blackhat/2 static review has a line-verified fix. See SECURITY.md for the reporting path and the threat model.

Guidelines when adding new features:

  • If it touches the enable flow, the CSRF / clickjacking defences apply
  • If it adds an endpoint, consider whether it needs a rate limit
  • If it handles user-supplied strings, validate them against a regex at the boundary
  • If it renders user-supplied content, use DOM APIs (not innerHTML + string) on the client side and autoescape on the server side

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. 9d ago First seen · 59 lines · 635 tokens per session scan A 14540a4e8790

Subscribe to this mod's changes

sncro-relay CLAUDE.md is an instructions file published in the GitHub repository scottconfusedgorilla/sncro-relay (0 stars, last pushed 3mo ago), licensed MIT. It adds 635 tokens to every session, about $0.0032 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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