Arc & Ledger Tax Tools

Screen an ITIN reason and application path

check_itin_eligibility

Read-only

Use this when someone asks whether a federal tax purpose may support an ITIN application or what a Form W-7 path generally requires. Returns a reason-specific screen, whether a return is commonly attached, current document-handling cautions, and official sources. Entity ownership or a bank request alone does not establish personal ITIN eligibility.

Input Schema

TableJSON Schema

Name	Required	Description
`reason`	Yes	Why you think a US taxpayer ID may be needed. file_us_tax_return = you must file a US return; owner_of_us_llc = you own a US LLC or corporation, which does not by itself establish a personal ITIN need; claim_treaty_benefit = a treaty claim may require a TIN; spouse_or_dependent = a US return may need a spouse or dependent TIN; third_party_withholding = a payer has a reporting or withholding requirement; open_us_bank_or_other = another reason.
`has_ssn`	Yes	Whether you already have, or are eligible for, a US Social Security Number. If yes, you cannot get an ITIN.
`is_foreign_national`	No	Whether you are a non-US citizen without US immigration status that grants an SSN. Defaults to true.

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.

Changed2 schema fields changedJul 26, 2026

changedInput schema / properties / reason / description

Previous value: -"Why you need a US taxpayer ID. file_us_tax_return = you must file a US return; owner_of_us_llc = foreign owner of a US LLC/corp needing an ID for filings; claim_treaty_benefit = reduce withholding under a tax treaty; spouse_or_dependent = of a US filer; third_party_withholding = a payer/bank needs your ID (W-8BEN); open_us_bank_or_other = other reason."New value: +"Why you think a US taxpayer ID may be needed. file_us_tax_return = you must file a US return; owner_of_us_llc = you own a US LLC or corporation, which does not by itself establish a personal ITIN need; claim_treaty_benefit = a treaty claim may require a TIN; spouse_or_dependent = a US return may need a spouse or dependent TIN; third_party_withholding = a payer has a reporting or withholding requirement; open_us_bank_or_other = another reason."

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

A4.1/5.0

Behavior4/5

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

Annotations already indicate readOnlyHint=true and destructiveHint=false. The description adds behavioral details beyond this, such as 'Returns a reason-specific screen, whether a return is commonly attached, current document-handling cautions, and official sources,' which aligns with a read-only screening tool and provides useful transparency.

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 description is concise (three sentences) and front-loaded with the primary usage case. It efficiently conveys key information without redundancy, though could be slightly more structured with bullet points for better readability.

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?

Given the tool has an output schema (not shown but indicated as true), the description sufficiently covers the tool's purpose, usage, and key outputs. It provides enough context for an agent to invoke correctly, leaving only minor gaps in explicit output details.

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 having a detailed description. The tool description does not add additional parameter semantics beyond the schema; it summarizes the purpose but does not enhance parameter understanding. Baseline score of 3 is appropriate given complete schema 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's purpose: screening ITIN eligibility and application paths. It uses specific verbs ('screen') and resources ('ITIN reason', 'Form W-7 path'), and the description distinguishes it from sibling tools like check_5472_obligation or check_fbar_fatca by focusing on ITIN eligibility.

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 ('when someone asks whether a federal tax purpose may support an ITIN application') and provides a negative use case ('Entity ownership or a bank request alone does not establish personal ITIN eligibility'). While it does not name alternative sibling tools directly, the context is clear enough for selection.

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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