ecfr-mcp

get_ancestry

Read-only

Retrieve the breadcrumb hierarchy path for a CFR section, part, or appendix, showing its title-to-section ancestry to identify the regulation it belongs to.

Instructions

Get the breadcrumb hierarchy path for a section, part, or appendix.

Returns ancestors from title down to the target node: title > chapter > subchapter > part > subpart > section. Useful for understanding where a section sits in the CFR hierarchy and what regulation it belongs to.

part/section/appendix accept int or string.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`date`	No
`part`	No
`section`	No
`appendix`	No
`title_number`	No

Output Schema

TableJSON Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

Changed3 schema fields changedv1.0.7Aug 20, 2026

addedInput schema / properties / appendix

Added value: +{
+  "anyOf": [
+    {
+      "type": "string"
+    },
+    {
+      "type": "integer"
+    },
+    {
+      "type": "null"
+    }
+  ],
+  "default": null,
+  "title": "Appendix"
+}

addedInput schema / properties / part / anyOf

Added value: +[
+  {
+    "type": "string"
+  },
+  {
+    "type": "integer"
+  },
+  {
+    "type": "null"
+  }
+]

addedInput schema / properties / section / anyOf

Added value: +[
+  {
+    "type": "string"
+  },
+  {
+    "type": "integer"
+  },
+  {
+    "type": "null"
+  }
+]

First observedv0.2.6May 16, 2026

TDQS

A3.9/5.0

Behavior4/5

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

The readOnlyHint and destructiveHint annotations already establish a safe read operation. The description adds useful behavioral context by specifying that the result is an ancestor chain from title down to the requested node. It does not contradict the annotations.

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 compact and front-loaded, with the core action and hierarchy shape stated early. The final sentence about accepted types is somewhat redundant with the schema but not excessive.

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

Completeness3/5

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

The description covers the return shape and intended use, and the output schema covers return values. However, with five optional-looking parameters and no required fields, it does not fully explain invocation constraints such as whether exactly one of part/section/appendix should be supplied or how date affects the ancestry path.

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

Parameters2/5

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

Schema description coverage is 0%, so the description must compensate, but it only restates that part/section/appendix accept int or string, which is already visible in the schema. It does not explain the date or title_number parameters, nor clarify how many targets should be supplied.

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 uses a specific verb and resource: 'Get the breadcrumb hierarchy path' for a section, part, or appendix. It clarifies the output shape ('title > chapter > subchapter > part > subpart > section') and distinguishes this ancestry lookup from the sibling structure/content tools.

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?

It gives a clear use case: 'useful for understanding where a section sits in the CFR hierarchy and what regulation it belongs to.' However, it does not explicitly name alternative sibling tools or state when not to use this tool.

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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