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GSA-TTS

mcp-server-gis-helper

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by GSA-TTS

Validate & Normalize GeoJSON Geometry

gis_validate_geometry
Read-onlyIdempotent

Validate and normalize GeoJSON geometry for GIS servers. Ensures WGS84 coordinates, unwraps Feature wrappers, closes polygon rings, and returns compact GeoJSON ready for downstream queries.

Instructions

Validate and normalize a GeoJSON geometry string for use with GIS servers.

Checks that the geometry is a supported type with valid WGS84 [lon, lat] coordinates, unwraps Feature/FeatureCollection wrappers, and closes any unclosed polygon rings. Returns a compact, single-line GeoJSON string that can be passed directly to the FEMA NFHL (nfhl_screen_flood_zone) or USGS National Map (hydro_find_waterways, etc.) tools.

Use when: you already have coordinates/GeoJSON and want to confirm it's valid and correctly formatted before querying another GIS server. Don't use when: you want to draw a shape interactively (use gis_open_map).

Returns on success: { "valid": true, "geometry": str, # compact GeoJSON string, ready to paste downstream "summary": { # geo_type, crs_epsg, vertex_count, part_count, ... # bbox [minLon,minLat,maxLon,maxLat], approx area/length } }

Error responses:

  • {"valid": false, "error": "..."} — invalid JSON, unsupported type, out-of-range coordinate (e.g. swapped lat/lon), or malformed BoundingBox.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
geometryYesGeoJSON geometry as a JSON string. Supported types: Point, MultiPoint, LineString, MultiLineString, Polygon, MultiPolygon. Also accepts a BoundingBox shorthand: {"type": "BoundingBox", "bbox": [minLon, minLat, maxLon, maxLat]}. A GeoJSON Feature or single-feature FeatureCollection is also accepted and unwrapped to a bare geometry. All coordinates must be WGS84 decimal degrees in [lon, lat] order.

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault

No arguments

Behavior5/5

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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false. The description adds substantial behavioral context: it unwraps Feature/FeatureCollection wrappers, closes unclosed polygon rings, checks WGS84 coordinate validity, returns a compact single-line GeoJSON string, and documents error scenarios. No contradiction with 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 well-structured with clear sections: a leading summary, usage guidance, success return format, and error responses. It is moderately long but every sentence serves a purpose—no fluff or repetition. Front-loaded with the core purpose and quickly readable.

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?

Given the tool's complexity (normalization, validation, coordinate system, wrappers, downstream compatibility), the description covers everything needed: what is validated, what transformations occur, the exact return shape (with a summary sub-object), and possible error messages. It is complete even without relying on the output schema.

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 schema description covers the only parameter (geometry) fully at 100% coverage, including supported types, BoundingBox shorthand, accepted wrappers, and coordinate order. The description adds behavioral normalization details (e.g., closing rings) but that falls under transparency rather than parameter semantics. With high schema coverage, a baseline of 3 is appropriate.

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 begins with a specific verb+resource: 'Validate and normalize a GeoJSON geometry string for use with GIS servers.' It clearly distinguishes itself from siblings by stating when to use it (before querying another GIS server) and when not to (interactive drawing, use gis_open_map). This is a precise, non-tautological purpose statement.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description provides explicit 'Use when' and 'Don't use when' guidance, naming the alternative tool (gis_open_map) for interactive drawing. It also lists downstream GIS tools that consume the output, making the usage context very clear.

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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