familysearch-mcp

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get_collection_fields

Read-only

Decode a collection's indexed record field codes into readable labels like Father's Name and Event Place before interpreting its records.

Instructions

Decode the field codes a collection's indexed records use.

An indexed record labels its values with codes rather than words — PR_FTHR_NAME, EVENT_PLACE, PR_NAME_SURN_ORIG. The codes are per-collection, and this is the dictionary that turns them into "Father's Name", "Event Place" and so on. Read it before interpreting a record from a collection you have not worked with.

Works without a token.

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": {
      "collection_id": "<collection_id>"
    },
    "name": "get_collection_fields"
  }
}

Input Schema

Name	Required	Description	Default
`collection_id`	Yes	Numeric collection id, e.g. '1417683' for the 1880 US census. Find one with search_collections.

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Sep 30, 2026

TDQS

A4.1/5.0

Behavior4/5

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

Annotations cover the safety profile (readOnlyHint=true, openWorldHint=true), and the description still adds real behavioral context: the codes are per-collection and it 'Works without a token', which tells the agent this call is safe pre-auth. It does not describe the return shape in detail, but that is a minor gap given 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?

Front-loads the purpose, then justifies it with concrete code examples and a when-to-use rule. The code examples (PR_FTHR_NAME, EVENT_PLACE) earn their place by making the concept tangible, though the three-line structure is slightly looser than a single tight sentence.

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?

For a single-param, no-output-schema tool, the description covers the essential gap: what the tool returns conceptually (a per-collection code-to-label dictionary) and when it is needed. Nothing critical for correct invocation is missing.

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% and the single collection_id param is already documented with an example ('1417683') and a pointer to search_collections. The description adds no parameter-level detail beyond the schema, so the baseline of 3 applies.

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 ('Decode the field codes a collection's indexed records use') and the value proposition is concrete: turning codes like PR_FTHR_NAME into 'Father's Name'. An agent can distinguish this from siblings such as get_collection or search_collections without opening the 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 usage context: 'Read it before interpreting a record from a collection you have not worked with.' This is an actionable when-to-use rule. It stops short of naming the alternative sequence explicitly (e.g. get_collection vs this), so it is not a full when/when-not routing statement.

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