eCFR

get_version_history

Read-only

Get the version history of a CFR section, subpart, or part.

Returns content_versions (each with date, amendment_date, issue_date,
identifier, name, substantive and removed), every version eCFR lists:
all of eCFR's pages are read, so Part 52's 2,264 versions are all
there. Versions are grouped by section, oldest first.

since_date/until_date (YYYY-MM-DD) keep versions dated in that range.
per_page (default 200, max 1000) and page step through long histories;
total_count and total_pages say how many there are.

'substantive' is eCFR's flag: true when the version's text differs from
the one before, including editorial edits such as citation fixes and
the "Link to an amendment published at ..." notice eCFR adds when a
rule is published; false when re-issued with no text change. To see
what actually changed, use compare_versions on the dates.

'removed' true means the section was removed on that date.

Version metadata and text snapshots may include dates before 2017.
Availability varies by title and section. Use the returned history
dates for reads or comparisons; a missing old snapshot produces an
availability error. A 2017-01-01 baseline often means unchanged since
before 2017.

part/subpart/section accept int or string.

Tool call template

This tool declares no required parameters. Add optional parameters from the input schema as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {},
    "name": "get_version_history"
  }
}

Input Schema

Name	Required	Description	Default
`page`	No
`part`	No
`section`	No
`subpart`	No
`per_page`	No
`since_date`	No
`until_date`	No
`title_number`	No

Output Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

First observedOct 21, 2026

TDQS

A4.6/5.0

Behavior5/5

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

Annotations already declare readOnly/openWorld/non-destructive, but the description adds substantial behavior beyond them: full enumeration of every eCFR page (implying latency/cost), grouping and oldest-first ordering, pagination limits with total_count/total_pages, the availability caveat and its error mode, and the meaning of the 2017-01-01 baseline. That is genuinely useful disclosure the agent could not infer.

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?

Front-loaded with purpose and return shape, then ordered into filtering, pagination, field semantics, and caveats. Dense and mostly waste-free, though the Part 52's 2,264-versions illustration and the substantive-flag explanation run longer than needed.

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?

For an 8-parameter read tool with an output schema and permissive annotations, the description covers cost, ordering, pagination, field meanings, and failure modes. Nothing an agent needs to call it correctly is missing.

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 carries the load and does: date format and range semantics for since_date/until_date, per_page default 200 and max 1000, page stepping, and the int-or-string flexibility for part/subpart/section. It leaves title_number (default 48) and the combination rules among part/subpart/section unexplained, so not a 5.

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?

States a specific verb and resource with scope ('version history of a CFR section, subpart, or part') and immediately names the sibling that answers a different question ('To see what actually changed, use compare_versions on the dates'). An agent can separate this from compare_versions or find_recent_changes without opening a schema.

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?

Gives clear operating context: use returned history dates for reads or comparisons, route to compare_versions for diffs, and expect an availability error when a pre-2017 snapshot is missing. It stops short of explicit when-not-to-use conditions or a full sibling comparison (e.g., vs. find_recent_changes), so a 4 rather than 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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