ASPERN: counterparty checks for agents

The policies a decision can be made under

list_policies

Read-onlyIdempotent

The policies evaluate_action can be run under, in full: every rule, its id and the sentence it checks. Published deliberately, including to the agents being evaluated — a rule nobody can read is a rule nobody can correct. Free.

Input Schema

Name	Required	Description	Default
No arguments

Output Schema

Name	Required	Description
`data`	Yes	Each policy with its slug, version, intent, ceiling, coverage floor and rules.
`meta`	No	How current this answer is and what it was read from: `freshness` and the ages behind it. Present on every answer from this server, whatever the tool.
`says`	No	What these policies are and are not. They are rules a decision is checked against, never a ranking of the agents evaluated under them.
`default`	No	The slug of the policy used when a call names none. Read it rather than assume: the default is an operator setting and can change without any tool changing.
`warnings`	No	Anything the server wants a caller to know about THIS answer before acting on it. Empty is the normal case and is not a guarantee.

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedOct 15, 2026

addedOutput schema / properties / meta

Added value: +{
+  "description": "How current this answer is and what it was read from: `freshness` and the ages behind it. Present on every answer from this server, whatever the tool.",
+  "type": "object"
+}

addedOutput schema / properties / warnings

Added value: +{
+  "description": "Anything the server wants a caller to know about THIS answer before acting on it. Empty is the normal case and is not a guarantee.",
+  "items": {
+    "type": "string"
+  },
+  "type": "array"
+}

Changed2 schema fields changedSep 29, 2026

addedOutput schema / properties / default / description

Added value: +"The slug of the policy used when a call names none. Read it rather than assume: the default is an operator setting and can change without any tool changing."

addedOutput schema / properties / says / description

Added value: +"What these policies are and are not. They are rules a decision is checked against, never a ranking of the agents evaluated under them."

AddedSep 27, 2026

TDQS

A3.8/5.0

Behavior4/5

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

Annotations already declare readOnly, idempotent, openWorld, and non-destructive, so the safety profile is covered. The description adds genuinely non-annotated context: the response is complete ('in full'), it is deliberately published to the evaluated agents, and it carries no cost ('Free'). It does not, however, describe pagination or size limits for a full rulebook.

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?

The operational content is front-loaded: what is returned, then the completeness and cost notes. The closing aphorism ('a rule nobody can read is a rule nobody can correct') is rhetorical rather than informational, but it is short and does justify the deliberate-publication behavior.

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

Completeness4/5

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

With an output schema present and annotations carrying the safety profile, the description only needs to say what the tool is for and what it returns, which it does well. The only gap is workflow placement relative to evaluate_action and the check_* family, which an agent would still have to infer.

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?

There are zero parameters and the empty schema is fully self-describing, so the baseline is 4. The description adds nothing parameter-related, but nothing is needed.

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

Purpose4/5

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

The description states the resource (the policies), the scope ('in full'), and the exact payload ('every rule, its id and the sentence it checks'), and it ties the resource to the sibling evaluate_action, which is the key disambiguator among 28 tools. The verb is only implicit ('the policies... can be run under'), so it reads as a resource description rather than an action, but an agent can still tell precisely what it returns.

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

Usage Guidelines3/5

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

By naming evaluate_action the description implies when this is relevant (fetching the rulebook that evaluate_action checks against), and 'Free' hints it is cheap to call. However, it never states when to call this versus the other check_/evaluate_ siblings, nor any sequencing guidance such as 'call before evaluate_action'.

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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