Agent Output Guard
Insert a deterministic validation layer between agents so outputs are checked before your main agent commits code, sends messages, or triggers side effects—without spending tokens on another LLM pass.
Overview
Agent Output Guard is a Ship-phase MCP server that validates and verifies other agents’ data before your workflow acts on it, with zero LLM spend for the check itself.
What is this MCP server?
- Validates and verifies data from other agents before downstream actions
- Marketed as zero LLM costs—rule-based verification rather than another model call
- npm @agenson-horrowitz/agent-output-guard-mcp v1.0.8, stdio transport
- GitHub: agenson-tools/agent-output-guard-mcp
- Registry server version 1.0.8 on MCP schema 2025-12-11
- Package and server version 1.0.8
- Transport type: stdio
- npm identifier: @agenson-horrowitz/agent-output-guard-mcp
What problem does it solve?
Multi-agent setups routinely forward unverified JSON or facts, and paying another LLM to double-check every handoff is slow and expensive.
Who is it for?
Indie builders running chained agents who need a cheap structural and policy check before tool calls that mutate repos, APIs, or customer data.
Skip if: Teams that only use a single agent with no intermediary outputs, or need full penetration testing rather than output verification.
What do I get? / Deliverables
After wiring the stdio MCP server into your agent chain, risky actions wait on deterministic validation of upstream agent output instead of blind trust.
- Stdio MCP validation step in multi-agent workflows
- Blocked or flagged actions when intermediary agent data fails checks
- Verification path that avoids additional LLM token usage for the guard itself
Recommended MCP Servers
Journey fit
Shipping safely means reviewing automated outputs before they hit production; this guard belongs on Ship because it blocks bad agent data at the last mile of multi-step flows. Review is the shelf for pre-action verification—schema checks and sanity rules on peer agent output fit review better than generic Build integrations.
How it compares
Deterministic agent-output verifier MCP, not an LLM-based reviewer skill or document ingestion parser.
Common Questions / FAQ
Who is Agent Output Guard for?
It is for developers composing multiple MCP or agent steps who need a non-LLM validation gate before executing commands on verified-looking but untrusted data.
When should I use Agent Output Guard?
Use it right before side-effecting steps—merges, deployments, billing calls—when another agent produced the payload and you want verification without another model invocation.
How do I add Agent Output Guard to my agent?
Install @agenson-horrowitz/agent-output-guard-mcp from npm, add it as a stdio MCP server in Claude Code or Cursor, and place it in the workflow between producer and consumer agents per the GitHub README.