APIbase

Macrostrat Bedrock Geologic Map Units

macrostrat.geology.map_units

Read-onlyIdempotent

Retrieve bedrock geologic map units at a specific latitude and longitude to get formation name, dominant lithology, description, age range, and recommended map color for surface geology analysis.

Instructions

Get the bedrock geologic map unit(s) at a specific point location (surface geology): formation/unit name, dominant lithology, description, age range, and recommended map color, sourced from compiled state/national geologic maps. Data: macrostrat.org/api/v2 /geologic_units/map, no auth required, CC BY 4.0.

Input Schema

Name	Required	Description
`lat`	Yes	Decimal degree latitude (WGS84)
`lng`	Yes	Decimal degree longitude (WGS84)
`scale`	No	Geologic map source scale (default returns the best-available match)

Output Schema

Name	Required	Description	Default
`error`	No	Present only when the call failed. Includes error code, message, request_id, and any provider-specific extras.
`result`	No	Tool response payload. Shape varies per tool — consult the tool description and inputSchema. May be an object, array, string, or number depending on the upstream provider response.

Schema Changelog

Changes observed during successful MCP inspections.

Addedv2.2.0Oct 29, 2026

TDQS

A4.3/5.0

Behavior4/5

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

The annotations already mark this as read-only, idempotent, and non-destructive. The description adds valuable behavioral context beyond those flags: no auth required, CC BY 4.0 licensing, the underlying endpoint, and the data provenance (compiled state/national geologic maps).

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 two sentences with no filler: the first sentence front-loads the operation and returned fields, and the second condenses endpoint, auth, and licensing. Every component earns its place.

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 a simple point lookup with robust annotations, a fully documented schema, and an output schema, the description is complete. It even includes the output field names and data source, so an agent has everything needed to call and interpret the tool correctly.

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?

The input schema covers all three parameters with clear descriptions, so the baseline is 3. The description does not add new parameter-level semantics beyond reinforcing that lat/lng identify a specific point location.

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 names a specific action ('Get') and resource ('bedrock geologic map unit(s) at a specific point location'), and lists the concrete output fields. The point-location/surface-geology framing clearly sets it apart from the sibling macrostrat search tools, which look up units, columns, or fossils by other criteria.

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 clearly establishes when the tool is appropriate: when an agent needs bedrock/surface geology at a single coordinate. It does not explicitly enumerate sibling alternatives or say when not to use them, so it falls just short of 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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