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familysearch-mcp

familysearch-mcp

by ianderso
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Python
Remote

get_descendancy

Read-only

Walk a person's descendants forward through generations to find records that name an ancestor when their own record is missing. Living descendants are marked restricted.

Instructions

Walk a tree person's descendants forward through the generations.

Useful for the sideways search: when a person's own record cannot be found, a descendant's obituary, probate or pension file often names him.

Living descendants are withheld and come back marked as restricted.

The shared tree is community-edited: anyone can change a profile, and conflations of same-named people are common. This is a hint where to look, not evidence: follow it to a record and cite that.

Requires an access 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": {
      "person_id": "<person_id>"
    },
    "name": "get_descendancy"
  }
}

Input Schema

NameRequiredDescriptionDefault
person_idYesFamilySearch person id to walk forward from.
generationsNoGenerations to return, 1 to 4. FamilySearch limits this one more tightly than ancestry, because a descendancy fans out.

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.1.0

TDQS

A4.4/5.0
Behavior5/5

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

Adds substantial behavior beyond the readOnly/openWorld annotations: living descendants are withheld and returned as restricted, the tree is community-edited with common same-name conflations, results are a hint rather than evidence, and an access token is required. This is exactly the context annotations cannot carry.

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 and proceeds in short, purposeful blocks, each earning its place. Slightly longer than strictly necessary but no filler.

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?

With no output schema, the description carries the return-value caveats (restricted living descendants) and the read caveat (hint, not evidence), plus the auth requirement. Nothing an agent needs before calling 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%, so person_id and generations are already documented in the schema. The description adds no parameter-level detail (no format, no syntax), so the baseline 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 ('walk a tree person's descendants forward') with the traversal direction made explicit, which cleanly distinguishes it from the sibling get_ancestry. An agent can tell what it does 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 a concrete use case for when this is valuable ('when a person's own record cannot be found, a descendant's obituary, probate or pension file often names him'), which is genuinely actionable. It stops short of naming alternatives explicitly or stating when not to use it.

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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