VesselAPI MCP Server

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get_vessels_in_radius

Retrieve vessels with AIS positions within a radius of a point during a specified time window (default 2 hours, max 4).

Instructions

Find vessels with an AIS position within a radius of a point during the time window (default the last 2 hours, at most 4 hours). The radius is in METRES, not nautical miles or kilometres.

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": {
      "latitude": "<latitude>",
      "longitude": "<longitude>",
      "radius": "<radius>"
    },
    "name": "get_vessels_in_radius"
  }
}

Input Schema

Name	Required	Description
`limit`	No	Results per page, 1 to 50. Defaults to 20.
`radius`	Yes	Search radius in METRES, maximum 100000 (100 km). One nautical mile is 1852 metres.
`timeTo`	No	End of the time window, RFC3339. Defaults to now. The window may not exceed 4 hours.
`latitude`	Yes	Center latitude
`timeFrom`	No	Start of the time window, RFC3339. Defaults to 2 hours ago. The window may not exceed 4 hours.
`longitude`	Yes	Center longitude
`nextToken`	No	Pagination token from previous response

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedv2.2.0Oct 30, 2026
- removedInput schema / additionalProperties
```
Removed value: -false
```

Changed7 schema fields changedv2.0.0Aug 20, 2026

changedInput schema / properties / limit / description

Previous value: -"Max results per page"New value: +"Results per page, 1 to 50. Defaults to 20."

addedInput schema / properties / limit / maximum
```
Added value: +50
```
addedInput schema / properties / limit / minimum
```
Added value: +1
```

changedInput schema / properties / limit / type

Previous value: -"number"New value: +"integer"

changedInput schema / properties / radius / description

Previous value: -"Radius in nautical miles"New value: +"Search radius in METRES, maximum 100000 (100 km). One nautical mile is 1852 metres."

changedInput schema / properties / timeFrom / description

Previous value: -"Start time filter in RFC3339 format (defaults to 2 hours ago)"New value: +"Start of the time window, RFC3339. Defaults to 2 hours ago. The window may not exceed 4 hours."

changedInput schema / properties / timeTo / description

Previous value: -"End time filter in RFC3339 format (defaults to current time)"New value: +"End of the time window, RFC3339. Defaults to now. The window may not exceed 4 hours."

Addedv1.3.0May 6, 2026

TDQS

A3.6/5.0

Behavior3/5

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

With no annotations, the description carries the full behavioral burden; it partially discharges this by disclosing the 2-hour default and 4-hour maximum window and the AIS-position basis. It says nothing about pagination behavior, result volume, or whether a point with no nearby vessels yields an empty set versus an error.

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?

Two sentences, front-loaded with the core operation and followed by the single most consequential gotcha (radius units). No filler.

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 7-parameter query tool with no output schema and no annotations, the description covers the key semantics an agent needs: what qualifies as a match, the time-window bounds, and the radius unit. Pagination and return shape are left to the schema, which is reasonable since nextToken is documented there.

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 coverage is 100%, so all seven parameters including limit, timeFrom/timeTo, and nextToken are already documented. The description's unit warning ('METRES, not nautical miles or kilometres') restates the schema's own emphasis but is useful reinforcement rather than new information, so baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('Find vessels with an AIS position within a radius of a point') plus the temporal scope, which naturally distinguishes it from get_vessels_in_area (polygon) and get_vessel_position (single vessel). It does not explicitly name a sibling, so it falls short of a 5.

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

Usage Guidelines3/5

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

Provides concrete usage constraints — the time window defaults to 2 hours and may not exceed 4 hours — which tells the agent how the tool behaves, but there is no explicit guidance on when to pick this over get_vessels_in_area or get_vessel_positions_batch.

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