Assay A2A, MCP & x402 Pre-Flight Verifier & Observatory

dev.agentdietPublished by agentdiet.devOfficial publisherv7.0.17Updated Oct 26, 2026

Live behavioral security verifier, schema auditor, and trust oracle for A2A, MCP & x402 agents.

The publisher's own server: AgentDiet AI Token Diet & Context Window Distiller

VerifiedStreamable HTTPWeb executableFinanceDeveloper ToolsSecurity & Monitoring

Overview

AI-generated overview

Remote verifier that lets an assistant pre-flight check MCP, A2A and x402 endpoints for liveness, schema drift and prompt-injection poisoning before calling…

What you can do
  • Gate a remote MCP, A2A or x402 endpoint before use: probe JSON-RPC reachability, hash the tools/list schema and scan for prompt-injection poisoning, with an optional expected hash that forces a deny verdict on mismatch.
  • Register or refresh an endpoint's public observatory dossier by running a live HTTP, agent-card and JSON-RPC inspection without policy gating.
  • Audit a paid x402 or A2A provider after payment, producing an HMAC-signed receipt that can confirm delivery or prove an SLA breach and bind a transaction hash.
  • Read historical conformance observations and pin or manage SHA-256 tools/list policy hashes in the Assay ledger for a target endpoint.
When to use it
Useful when an agent is about to call or pay third-party MCP, A2A or x402 services and you want a live check of reachability, tool-schema stability and injection risk first, or when you need evidence of delivery or an SLA breach after a payment.
Requirements
A remote streamable HTTP endpoint; no authentication, environment variables or headers are declared. Targets must be public HTTPS origins, since private IPs are rejected. Network access to the Assay service and to the endpoints being probed.
Before you install
Probing submits third-party endpoint addresses to the Assay service, which keeps a public dossier and timestamped observation ledger for them. Verification can bind a payment transaction hash, so treat transaction identifiers as sensitive. Pinning a tools/list hash changes stored policy for that target.

Installation

In SourceWeft

  1. Open Assay A2A, MCP & x402 Pre-Flight Verifier & Observatory in the dashboard and add it to a workspace.
  2. Enable the server for the chats that should use its tools.

Web executable via Streamable HTTP. Remote servers run from the web runtime once configured in a workspace.

Use with an agent

Paste this prompt into Claude Code, Codex, Cursor or another agent — or into SourceWeft chat. The agent reads this server's install guide, shows you its publisher, endpoint and sign-in, and adds it to your client once you agree. Keys never go into a command.

Read https://sourceweft.com/mcp/dev.agentdiet%2Fassay/install.md and connect the MCP server it describes to my client. Before changing any config, show me its publisher, endpoint and sign-in method and wait for my OK. Never put an API key in a command or in a file I would commit; ask me where it should come from.

Read the install guide the agent follows

Other MCP clients

Add this to your client's mcpServers config.

{
  "mcpServers": {
    "assay-a2a-x402-pre-flight-verifier-obser": {
      "type": "http",
      "url": "https://assay.agentdiet.dev/mcp"
    }
  }
}

README

Assay — A2A & MCP Provider Assurance Observatory

[Assay Badge]

Live Observatory: https://assay-207908449630.us-central1.run.app

Assay continuously probes remote MCP, A2A, and x402 endpoints to verify liveness, pin canonical SHA-256 tools/list schema hashes (detecting silent MCP Rug Pulls), and scan for prompt-injection tool poisoning before your agent pays or executes a tool.

MCP Endpoint

  • Streamable HTTP MCP: https://assay-207908449630.us-central1.run.app/mcp
  • Pre-Flight REST API: POST https://assay-207908449630.us-central1.run.app/v1/preflight
  • Live Leaderboard: GET https://assay-207908449630.us-central1.run.app/v1/leaderboard

Source: README.md at commit fd42696

Tools

4

assay_preflight

Pre-Flight MCP & A2A Security Gate

Gate a remote MCP, A2A, or x402 endpoint before calling or paying it by probing live JSON-RPC reachability, hashing tools/list (SHA-256), and scanning for prompt-injection poisoning. When expected_tools_hash is provided, any mismatch against the live tools/list digest forces verdict='deny' to block silent schema rug-pulls; when omitted, verdict reflects liveness and injection safety alone. Read-only gate; first 5 calls/IP are free and quota-exceeded calls return a 402 top-up prompt. Use before tool execution or payment; to register or refresh public leaderboard telemetry use assay_probe; to read or pin stored policy hashes use assay_get_ledger_policy; after payment use assay_verify_delivery. Example: target='https://agentdiet-72343955726.us-central1.run.app/mcp'.

Parameterstargetrequiredexpected_tools_hash

assay_probe

Register & Refresh Endpoint Conformance Telemetry

Register a new remote MCP, A2A, or x402 endpoint or refresh its public Assay Observatory dossier by running a live HTTP, agent-card, and JSON-RPC tools/list inspection without policy gating. Target must be a public HTTPS origin (private IPs are rejected with a 400 error); each call appends a timestamped observation and increments rug_pulls if tools_hash drifted since the prior stored observation. Writes to the public ledger; first 5 calls/IP are free and retries are idempotent on steady schemas. Use to onboard or re-index a server; for pre-call allow/deny gating use assay_preflight; for historical observations or hash pinning use assay_get_ledger_policy; for post-payment disputes use assay_verify_delivery. Example: target='https://agentdiet-72343955726.us-central1.run.app/mcp'.

Parameterstargetrequired

assay_verify_delivery

Verify Post-Payment x402 Delivery & Mint SLA Receipt

Audit a paid x402 or A2A provider after payment to confirm delivery or prove an SLA breach with an HMAC-SHA256 signed receipt. Passing status_code >= 500 forces verdict='sla_breach_confirmed' even if the live re-probe succeeds, while passing tx_hash cryptographically binds your Base or Solana payment signature into the receipt (omitting tx_hash still verifies liveness and issues a probe-bound receipt). Non-destructive; first 5 calls/IP are free and failed target connections do not throw tool errors. Use only after paying a provider; before payment use assay_preflight; for public indexing use assay_probe; for policy history use assay_get_ledger_policy. Example: target='https://agentdiet-72343955726.us-central1.run.app/mcp'.

Parameterstargetrequiredtx_hashstatus_code

assay_get_ledger_policy

Query Historical Ledger & Pin Expected Schema Hashes

Retrieve historical conformance observations and manage pinned SHA-256 tools/list policy hashes in the Assay ledger for a target endpoint. When expected_tools_hash is provided, it pins that 64-hex digest as the target's baseline policy and compares it against the latest stored observation; when omitted, it returns the stored dossier and last 20 drift observations without network probing unless the target is unindexed. Idempotent; first 5 calls/IP are free. Use to audit historical drift or pin mcp-lock.json hashes; for live pre-execution gating use assay_preflight; for live re-indexing use assay_probe; for post-payment SLA receipts use assay_verify_delivery. Example: target='https://agentdiet-72343955726.us-central1.run.app/mcp'.

Parameterstargetrequiredexpected_tools_hash

Version history

2
  1. v7.0.17LatestOct 21, 2026
  2. v0.7.32Oct 19, 2026

Score

100% of the applicable checks met

How complete this listing is, computed from the registry entry, the endpoint and public sources. Not a rating of the server and not a statement that it is safe or working today: reachability is a dated check, and no installs or reviews go into the score.

  • Reached in the last 30 daysRequired25 pts
  • Auth declaredRequired10 pts
  • Tools listedRequired15 pts
  • DescriptionRequired15 pts
  • Logo10 pts
  • Documentation15 pts
  • License10 pts

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