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sentinel: Instructions file for Claude Code

CLAUDE.md

sentinel CLAUDE.md is an instructions file for Claude Code from patsypppe/sentinel. It costs 925 tokens per session, scanned A, original, MIT.

A set of instructions for working on the Sentinel repository, which contains a Go MCP server and a Python test harness. MCP is a standard way for software tools to communicate with AI clients.

In plain words
What is it for?
Use it when changing or testing the Sentinel broker or its conformance harness, especially work governed by the repository’s MCP specification.
Why use it?
It gives coding agents the repository’s rules and constraints, including how stateless behaviour, retries, and deterministic results must work.

Instructions file for Claude Code

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

This is patsypppe/sentinel's own configuration. It tells Claude Code how to work on sentinel 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 sentinel configures →

not rated 1repo changed 8d ago A scan 925 tokens original MIT
View source ↗ patsypppe/sentinel
Reuse

Borrowing it

Nothing to install: this file belongs to patsypppe/sentinel. 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/patsypppe/sentinel/main/CLAUDE.md
Clone the repo
git clone --depth 1 https://github.com/patsypppe/sentinel

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.

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README.md
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Your own site
<a href="https://agentmods.dev/instructions/patsypppe/sentinel/claude-md"><img src="https://agentmods.dev/badge/instructions/patsypppe/sentinel/claude-md/github.svg" alt="Measured on agentmods" height="20"></a>

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.

agentmods 80×15 button for sentinel CLAUDE.md

Your own site · 80×15
<a href="https://agentmods.dev/instructions/patsypppe/sentinel/claude-md"><img src="https://agentmods.dev/badge/instructions/patsypppe/sentinel/claude-md.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 925 This file is loaded in full into every session.
When invoked 925 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 $0.00925 $0.00925
Opus 5.5 $0.00370 $0.00370
Sonnet 5.5 $0.00185 $0.00185
Haiku 4.5 $0.00093 $0.00093

Measured 8d ago against content hash f6be89eab338, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

sentinel 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 8d 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 · 70 lines

How it starts

The opening of the file, as written. The whole thing — 70 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Sentinel — working instructions

Two products in one repository:

  • broker/ — a Go MCP server built natively on the stateless MCP 2026-07-28 specification.
  • harness/ — sentinel, a Python conformance harness that grades any MCP server.

The spec is docs/HANDOFF.md (SN-HND-001). Where this repository and the MCP specification disagree, the spec wins.

The four rules

  1. Stateless. Handles are data, never credentials. No session, nothing keyed by connection. Cross-call state is a server-minted handle passed as an ordinary tool argument. Possession of a handle is not authentication — every resolution re-verifies principal and tenant.
  2. No server-initiated requests. MRTR only, and it must be idempotent. resultType: "input_required" + inputRequests; the client retries with inputResponses. Correlation is the sealed requestState, never the JSON-RPC id. A duplicate retry returns the recorded result and performs zero additional side effects.
  3. Deterministic where the spec asks for determinism. 100 tools/list calls → one SHA-256. Every list/read result carries ttlMs and cacheScope. Mcp-Method required on every POST; Mcp-Name on tools/call, resources/read, prompts/get only.
  4. Every invocation is audited; no token is trusted that was not issued for this server. Validate the audience exactly. Never forward an inbound token downstream. If the audit write fails, the invocation fails.

Never cut

resultType + serverInfo on every result · handle binding · MRTR idempotency · the audit row · the non-conformant fixture server.

Single-source files (audit the security posture by reading three files)

File Sole authority for
mcp/envelope/errors.go every error code
mcp/handles/resolve.go making a handle usable
mcp/authz/audience.go accepting a token

Hard constraints

  • Structs, never map[string]any for anything serialized deterministically. json.RawMessage for pass-through — a number through any becomes float64 and breaks hashes.
  • Error codes -32020…-32099 are reserved for the spec, and -32000…-32019 is the sub-range it retired — new implementations SHOULD NOT use it at all. Ours live at 1000…1019, outside the JSON-RPC reserved range entirely.
  • The harness must never import broker internals and must run against any endpoint URL.
  • The probe is a deliberately literal MCP client. No MCP SDK — an SDK that helpfully adds Mcp-Method makes the rule requiring Mcp-Method untestable.
  • An unverifiable MUST returns INDETERMINATE, never a false pass.
  • No model API key is required anywhere. Broker serves tools; it does not call models.
  • Do not add: a web framework, an ORM, or a JSON-RPC library that hides the envelope.

Read the full file on GitHub · 70 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. 8d ago Changed f6be89eab338
  2. 2mo ago First seen · 70 lines · 925 tokens per session scan A 39cc4702a610

Subscribe to this mod's changes

sentinel CLAUDE.md is an instructions file published in the GitHub repository patsypppe/sentinel (1 stars, last pushed 5d ago), licensed MIT. It adds 925 tokens to every session, about $0.0037 per session on Opus 5.5. 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.

Goaudit-logconformance-testingdeveloper-toolsenvoyjson-rpc
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