Arc & Ledger Tax Reference

Check FBAR and FATCA obligations

check_fbar_fatca

Read-only

Use to screen general FBAR and Form 8938 thresholds from aggregate balance, filing status, residence, and account-count facts. Do not request account numbers, institution names, or statements.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "max_aggregate_foreign_balance_usd": "<max_aggregate_foreign_balance_usd>",
      "filing_status": "<filing_status>",
      "lives_abroad": "<lives_abroad>"
    },
    "name": "check_fbar_fatca"
  }
}

Input 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

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	Official IRS or FinCEN authority to review before relying on the result.
`server_version`	No	Server release that produced this response (matches GET /version).

Schema Changelog

Changes observed during successful MCP inspections.

First observedJul 28, 2026

TDQS

A4.2/5.0

Behavior4/5

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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the tool is known to be safe and non-destructive. The description adds value by specifying the type of data to avoid requesting (account numbers, etc.), which is a behavioral constraint beyond the annotations. 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?

The description is only two sentences, no wasted words. It front-loads the purpose and includes a useful constraint. Every sentence earns its place.

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 5 parameters, 100% schema coverage, and an output schema existing, the description covers the essential context: what inputs to provide and what to avoid. It does not need to explain outputs since the output schema handles that. Minor gap: no mention of potential limitations or edge cases, but still complete enough for this tool's complexity.

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 description coverage is 100%, so the schema already documents all 5 parameters well. The description does not add new parameter-specific details but summarizes the key inputs (aggregate balance, filing status, residence, account-count). This adds minimal additional meaning beyond the schema, so score is baseline 3.

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 screens general FBAR and Form 8938 thresholds from specific facts. It uses a specific verb 'screen' and identifies the resource 'thresholds'. The sibling tools include other check tools, and this one is clearly distinct due to its focus on FBAR/FATCA.

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 states when to use the tool (to screen thresholds from aggregate balance, filing status, residence, and account-count facts) and includes a negative guidance ('Do not request account numbers, institution names, or statements'). However, it does not explicitly mention alternatives or when not to use it, which would elevate it to a 5.

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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