ecfr-mcp

compare_versions

Read-only

Compare CFR section text at two dates to identify changes from regulatory amendments. Returns side-by-side parsed text for diffing.

Instructions

Compare the text of a CFR section at two different dates.

Useful for understanding what changed in a regulatory amendment. Returns the parsed text at both dates side by side. You can then diff the paragraphs to identify specific changes.

Dates must be in YYYY-MM-DD format and within the eCFR's tracking range (January 2017 to present). Both dates must not exceed the title's up_to_date_as_of value.

This tool always returns the section-level XML parsed -- pass a small section_id like '15.305', not a whole part. Whole-part comparisons can exceed 100 KB per side.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`chapter`	No
`date_after`	Yes
`section_id`	Yes
`date_before`	Yes
`title_number`	No

Output Schema

TableJSON Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedv1.0.7Aug 20, 2026

addedInput schema / properties / chapter / anyOf

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

addedInput schema / properties / section_id / anyOf

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

First observedv0.2.6May 16, 2026

TDQS

A4.6/5.0

Behavior5/5

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

The description goes well beyond the annotations. It discloses that the tool returns parsed section-level XML side by side, warns about size limits for whole-part comparisons, and specifies the date range and validation constraints. This additional behavioral context (e.g., 'always returns', 'can exceed 100 KB per side') is valuable for the agent, and there is no contradiction with the readOnlyHint and destructiveHint annotations.

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 efficient: four sentences, front-loaded with the primary purpose, then usage context, constraints, and a warning. Each sentence adds necessary information without redundancy. It is concise yet thorough, making it easy for an agent to parse quickly.

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's complexity and the existence of an output schema, the description covers the essential contextual details: what it returns, how to pass parameters, and key limitations. It does not explain the exact output structure (handled by schema) or the order of date_before vs date_after, but that is minor. Overall, it is sufficiently complete for an agent to call the tool correctly.

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?

With 0% schema description coverage, the description must compensate for parameter meaning. It explains section_id format ('like '15.305'', small section only) and date format and range, which are the core parameters. It does not elaborate on chapter or title_number, but these have defaults and are somewhat inferable from the CFR context. Thus, it adds meaningful semantics for the most critical parameters but not all.

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 compares the text of a CFR section at two different dates. It uses a specific verb ('Compare') and resource ('CFR section'), and the purpose is further clarified as understanding regulatory amendments. It distinguishes itself from siblings like get_version_history by focusing on text comparison rather than just version lists.

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 provides clear usage context ('Useful for understanding what changed in a regulatory amendment') and includes practical constraints (date format, range, up_to_date_as_of limit). However, it does not explicitly name alternatives or state when not to use this tool, so it falls short of the highest level which requires explicit when/when-not guidance.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

Deploy Server