Atlas MCP

atlas-mcp

Pre-action authorization for AI agents, as an MCP server.

Before an agent deletes data, deploys, or spends money, it asks Atlas. Atlas checks the request against a signed delegation chain and answers permit, deny or escalate, with a receipt. After acting, the agent reports what really happened with atlas_commit_effect. Every step lands in a hash-chained, ML-DSA-65-signed audit log.

$ npx -y @corpussanctum/atlas-mcp demo

You (alice) delegate to claude: database work in STAGING only.

Claude: delete rows in staging -> PERMIT rcpt_ec14… authorized by 1-link delegation chain from user:alice

Claude: delete rows in PRODUCTION -> DENY rcpt_876f… effect targets environment 'production'; delegated authority (grant grt_c9c8…) only permits staging

Claude: write to staging (grant says writes need a human) -> ESCALATE rcpt_a8d7… action 'db.write' requires human approval

Quickstart (5 minutes)

1. Register the server.

Claude Code:

claude mcp add atlas -- npx -y @corpussanctum/atlas-mcp

Claude Desktop (claude_desktop_config.json), or any MCP client:

{ "mcpServers": { "atlas": { "command": "npx", "args": ["-y", "@corpussanctum/atlas-mcp"] } } }

Codex (~/.codex/config.toml):

[mcp_servers.atlas]

command = "npx" args = ["-y", "@corpussanctum/atlas-mcp"]

2. Delegate authority. You, the principal, issue a grant to the agent:

npx -y @corpussanctum/atlas-mcp grant --principal user:alice --subject agent:claude \

--allow 'db.*' --env staging --escalate db.write --ttl-hours 8

prints the grant JSON; note its "id" (grt_…)

3. Tell the agent the rules. Add to CLAUDE.md / AGENTS.md (see examples/CLAUDE.md.snippet):

Before any destructive, production, deploy or spending action, call atlas_authorize with agent agent:claude, principal user:alice, delegation_chain ["grt_…"], the action and every effect. Proceed only on permit. Afterwards call atlas_commit_effect.

4. Approve escalations as the human. Approval is deliberately not an MCP tool, so an agent cannot approve itself:

npx -y @corpussanctum/atlas-mcp resolve rcpt_a8d7… approve

npx -y @corpussanctum/atlas-mcp verify # check the audit chain and signatures

Tools

How decisions work

• A grant says: grantor → subject may do allow actions (minus deny), only in environments, only on resources, with escalate actions needing a human. Grants are signed by the local issuer key and recorded in the audit log.
• A chain runs principal → agent → sub-agent. It must be unbroken, unexpired, unrevoked, and may only narrow from link to link. A child grant that widens its parent is rejected.
• Intersection semantics: every link must independently allow the action and each effect. Revoking any link kills everything below it, including receipts already issued but not yet committed (they become revoked).
• Fail closed: unknown grants, bad signatures, missing environments under an environment-restricted grant, a request with no effects under an environment- or resource-restricted grant, and malformed requests all deny. The server trusts its own recorded copy of a grant, never the caller's.
• Receipts expire after 15 minutes. A permit/approval covers the stated effects only.

Enforce it: the Claude Code hook

The MCP tools are a gate the agent *chooses* to call. The hook makes the check unskippable for Claude Code: it runs outside the model on every gated tool call, so the agent cannot forget, or talk its way past, a deny.

npm i -g @corpussanctum/atlas-mcp       # a global install avoids npx startup cost on every tool call

atlas-mcp hook init --principal user:alice

hook init writes ~/.atlas-mcp/hook.json, issues a starter grant (30 days; environments dev and staging; shell.deploy and shell.delete ask first), and prints the settings.json block to paste into ~/.claude/settings.json.

What happens on each tool call

The PostToolUse and PostToolUseFailure hooks then commit the receipt (success or failure) to the signed audit log, even when the command outlived the receipt's 15 minutes; a call whose grant was revoked while it ran is recorded as a violation. Check it any time with atlas-mcp verify. If you set the hook up before PostToolUseFailure was part of the printed block, add it, or failed calls go unrecorded.

Tuning

Edit ~/.atlas-mcp/hook.json:

{

"agent": "agent:claude-code", "principal": "user:alice", "delegation_chain": ["grt_…"], "default_environment": "dev", "environments": [{ "match": "(?<![a-z])(prod|production|live)(?![a-z])", "environment": "production" }], "rules": [{ "tool": "^Bash$", "match": "^make release", "action": "shell.deploy", "effect_type": "deploy" }], "on_permit": "defer" }

on_permit: "allow" lets an Atlas permit skip Claude Code's own prompt. The default, defer, keeps Claude Code's prompts as a second layer.

What it does not do (read this)

• Classification is pattern matching. A command Atlas doesn't recognise is plain shell.exec, and environment is inferred from words in the command (prod, production, staging, also inside names such as PROD_DB_URL or db_prod). ./deploy.sh or a connection string with no environment word passes as dev. Add rules and environments for your own tooling. This is a speed bump against mistakes and a record for audit, not a defence against an agent actively hiding its intent.
• Effects are as classified, not observed. The audit log records what Atlas judged the call would do, not what the process really did.
• Hook failures. The hook answers deny when it can catch its own error (missing config, bad grant). A hard crash or timeout is not blocked by Claude Code unless your build supports "onFailure": "block" on the hook handler (documented for recent versions); add it to both hook entries if yours does.
• Permission modes. Claude Code's docs don't say whether a hook deny survives --permission-mode bypassPermissions. We tested it on Claude Code 2.1.296 (Claude Code): a denied command did not run under bypassPermissions (the control command ran and was committed). Retest after upgrading Claude Code.
• Self-protection is partial. Reads and edits of ~/.atlas-mcp, commands and MCP tool arguments that name it, and the atlas-mcp grant, revoke, resolve and hook init commands are refused, but a shell can reach a file or a binary by many routes. Reads are only checked if Read|Grep|Glob are in your PreToolUse matcher: if you set the hook up before this was added, update the matcher to the one hook init prints. Run agents as a different OS user from the one that owns the data directory if that matters to you.
• Claude Code only. Other clients need their own enforcement point.

Read this before you rely on it

• This is a gate the agent consults, not a sandbox. On its own, an MCP tool cannot stop an agent that decides not to call it, or that lies about its effects. v0.1 gives you a signed, verifiable record and a decision to enforce *with*: for Claude Code, use the hook above to make it binding; elsewhere pair it with a tool proxy or network/credential isolation. atlas_commit_effect catches and records the mismatches it is told about.
• The issuer key sits unencrypted in ~/.atlas-mcp/issuer.json (mode 0600). Protect the directory like an SSH key. Anyone who can read it can forge grants.
• The audit log detects edits, removals and reordering; truncation only partly. A signed head (audit.head) records the newest entry, so verify notices entries cut from the end, and Atlas refuses to authorize on top of a shortened log. Someone who deletes the head file as well leaves a shorter log that still verifies (with a warning). For stronger evidence, copy audit.head somewhere the agent's account cannot write.
• Local operator approval = local shell access. There is no remote approval channel in v0.1.
• Not a compliance certification. Cryptographic choices follow the parent project's assumptions; no external audit has been done.

Data and config

ATLAS_MCP_DATA_DIR (default ~/.atlas-mcp) holds issuer.json, audit.jsonl and its signed head audit.head. Nothing leaves the machine.

Docker

docker build -t atlas-mcp .

docker run -i --rm -v atlas-data:/data atlas-mcp

Relationship to Atlas Protocol

atlas-protocol is the full governance gatekeeper (Telegram operator relay, 96-rule policy engine, agent identity registry, behavioral baselines, proximity). atlas-mcp is its smallest useful piece, extracted so you can install it in one line.

Development

npm install && npm test

Apache-2.0.