assay

Pre-Flight MCP & A2A Security Gate

assay_preflight

Idempotent

Evaluate a remote MCP, A2A, or x402 endpoint before calling or paying it. Probes live JSON-RPC reachability, hashes tools/list (SHA-256), checks expected_tools_hash for silent rug-pull drift, and scans for prompt-injection poisoning. Returns {verdict ('allow'|'warn'|'deny'), reason, receipt ('asr_rcpt_...'), dossier}. Use before tool execution or payment; for post-payment disputes use assay_verify_delivery; for raw telemetry indexing use assay_probe. First 5 calls/IP free.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`target`	Yes	Public HTTPS URL of the remote MCP server, A2A agent, or x402 endpoint to inspect (e.g. 'https://tandem.ac/mcp'). Private and loopback IPs are blocked.
`expected_tools_hash`	No	Optional 64-char SHA-256 hex digest of the canonical MCP tools/list schema from mcp-lock.json. If set and the live hash differs, verdict is 'deny'.

Output Schema

TableJSON Schema

Name	Required	Description	Default
`reason`	No
`dossier`	No
`receipt`	Yes
`verdict`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedOct 17, 2026

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "properties": {
+    "dossier": {
+      "type": "object"
+    },
+    "reason": {
+      "type": "string"
+    },
+    "receipt": {
+      "type": "string"
+    },
+    "verdict": {
+      "type": "string"
+    }
+  },
+  "required": [
+    "verdict",
+    "receipt"
+  ],
+  "type": "object"
+}

Changed6 schema fields changedOct 17, 2026

changedInput schema / properties / expected_tools_hash / description

Previous value: -"expected_tools_hash for assay_preflight"New value: +"Optional 64-char SHA-256 hex digest of the canonical MCP tools/list schema from mcp-lock.json. If set and the live hash differs, verdict is 'deny'."

addedInput schema / properties / expected_tools_hash / maxLength
```
Added value: +128
```
addedInput schema / properties / expected_tools_hash / minLength
```
Added value: +0
```

changedInput schema / properties / target / description

Previous value: -"target for assay_preflight"New value: +"Public HTTPS URL of the remote MCP server, A2A agent, or x402 endpoint to inspect (e.g. 'https://tandem.ac/mcp'). Private and loopback IPs are blocked."

addedInput schema / properties / target / maxLength
```
Added value: +512
```
addedInput schema / properties / target / minLength
```
Added value: +8
```

First observedOct 16, 2026

TDQS

A4.8/5.0

Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Goes well beyond the annotations: it discloses the exact probing behavior (live JSON-RPC reachability), the drift comparison against expected_tools_hash that forces a 'deny' verdict, the outcome vocabulary (allow/warn/deny), and a rate-limit/quotient ('First 5 calls/IP free'). Annotations cover safety/idempotency, and the description adds the operational mechanics without contradicting readOnlyHint=false or destructiveHint=false.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loads the core purpose in the first sentence, then packs checks, return shape, routing, and quota into a dense paragraph. Every clause is informative, though the run-on structure across three sentences makes it slightly cramped rather than perfectly scannable.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Output schema exists so return-value documentation is optional, yet the description still previews the verdict payload. Combined with clear usage routing, behavioral mechanics, and the free-tier limit, an agent has everything needed to select and invoke the tool correctly without opening the schema.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the baseline is 3; the description earns above baseline by supplying the rationale for expected_tools_hash ('silent rug-pull drift') that the schema only describes mechanically, plus the endpoint scope (MCP/A2A/x402) for target. It does not, however, add format or syntax detail beyond the schema.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description names a specific verb (evaluate/inspect) and resource (remote MCP, A2A, or x402 endpoint) and enumerates the concrete checks performed: JSON-RPC reachability, SHA-256 tools/list hashing, drift detection, injection scanning. It also distinguishes itself from siblings by naming assay_verify_delivery and assay_probe as alternatives.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Explicitly states when to use it ('before tool execution or payment') and routes to the alternatives with their own trigger conditions ('post-payment disputes use assay_verify_delivery; for raw telemetry indexing use assay_probe'). Nothing is left to inference.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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