Arc & Ledger Tax Tools

Check FBAR and FATCA obligations

check_fbar_fatca

Read-only

Use this when a user has foreign bank accounts, assets, or unfiled foreign-account reports and needs to know their US reporting obligations (FBAR / FinCEN 114 and Form 8938 / FATCA), thresholds, penalty exposure, and catch-up options.

Input Schema

TableJSON Schema

Name	Required	Description
`lives_abroad`	Yes	True if your tax home is outside the United States (higher Form 8938 thresholds apply).
`account_count`	No	Number of foreign accounts, if known.
`filing_status`	Yes	Your US tax filing status.
`unfiled_years`	No	How many past years of FBARs you have NOT filed but should have. 0 or omitted if current.
`max_aggregate_foreign_balance_usd`	Yes	The highest combined value of ALL your foreign financial accounts at any point during the year, in USD.

Output Schema

TableJSON Schema

Name	Required	Description
`relay`	Yes	Instruction to the calling assistant: relay figures and dates verbatim (identical on every response).
`next_step`	Yes	A single review link appropriate to this server surface.
`disclaimer`	Yes	General-information disclaimer (identical on every response).
`source_url`	Yes	The arcandledger.com page that backs this answer.
`server_version`	No	Server release that produced this response (matches GET /version).

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedJul 26, 2026

changedOutput schema / properties / next_step / description

Previous value: -"A single human handoff to the firm."New value: +"A single review link appropriate to this server surface."

Changed2 schema fields changedJul 13, 2026

addedOutput schema / properties / relay

Added value: +{
+  "description": "Instruction to the calling assistant: relay figures and dates verbatim (identical on every response).",
+  "type": "string"
+}

changedOutput schema / required

Previous value: -[
-  "disclaimer",
-  "source_url",
-  "next_step"
-]New value: +[
+  "disclaimer",
+  "relay",
+  "source_url",
+  "next_step"
+]

Changed1 schema field changedJul 12, 2026

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "additionalProperties": true,
+  "properties": {
+    "disclaimer": {
+      "description": "General-information disclaimer (identical on every response).",
+      "type": "string"
+    },
+    "next_step": {
+      "description": "A single human handoff to the firm.",
+      "properties": {
+        "label": {
+          "type": "string"
+        },
+        "url": {
+          "type": "string"
+        }
+      },
+      "required": [
+        "label",
+        "url"
+      ],
+      "type": "object"
+    },
+    "server_version": {
+      "description": "Server release that produced this response (matches GET /version).",
+      "type": "string"
+    },
+    "source_url": {
+      "description": "The arcandledger.com page that backs this answer.",
+      "type": "string"
+    }
+  },
+  "required": [
+    "disclaimer",
+    "source_url",
+    "next_step"
+  ],
+  "type": "object"
+}

First observedJul 8, 2026

TDQS

A4.3/5.0

Behavior4/5

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

Annotations already declare readOnlyHint=true. The description adds behavioral context by stating the tool checks obligations, thresholds, and penalties, confirming it is non-destructive. No contradictions.

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

Conciseness5/5

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

A single, well-structured sentence that front-loads the use case and packs all necessary information efficiently without waste.

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?

Given the complexity of FBAR/FATCA, the description covers when to use, what is checked (thresholds, penalties, catch-up), and implies the output will inform obligations. With output schema present, this is complete.

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

Parameters3/5

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

Schema coverage is 100% with each parameter described. The tool description adds minimal extra meaning beyond the schema, meeting the baseline for full coverage.

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 clearly states the tool is for checking US reporting obligations (FBAR/FATCA) for foreign accounts, with specifics on thresholds, penalties, and catch-up options. It distinctively targets foreign account issues, differentiating from sibling tools like check_5472_obligation.

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

Usage Guidelines4/5

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

The description explicitly starts with 'Use this when a user has foreign bank accounts...' providing clear usage context. However, it does not explicitly mention when not to use or compare to alternatives, leaving some room for improvement.

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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