get_vessel_positions

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

With no annotations, the description carries full responsibility and excels: it discloses the AISStream.io WebSocket source, the required AISSTREAM_API_KEY in .env, the ~8-second listening time, and that it returns a snapshot. These are critical operational details not visible in the schema.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is well-structured into source, region list, args, and returns. The region list is long but necessary for the agent to know valid inputs, and every sentence adds value with no filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

The tool has no output schema, so the description must explain return values. It does so explicitly: dict with vessel_count, underway/anchored breakdown, and per-vessel details like MMSI, name, position, speed, course, and nav status. Combined with prerequisites and latency, the agent has everything needed to invoke and interpret results.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 0%, so the description must explain parameters. It fully documents the region parameter with all valid named regions and suggests list_major_ports() for context, and it explains max_vessels with its default. This adds significant meaning beyond the bare schema.

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

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

The description clearly states it gets live vessel positions from AIS transponder data for a shipping region, using a specific verb and resource. This is distinct from sibling tools like get_port_congestion or get_port_weather, so no confusion arises.

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

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

The description provides clear context for when to use the tool, tying it to route assessment and listing named regions. It also references list_major_ports() for context, but it doesn't explicitly state when not to use the tool or directly name alternatives for the same task.

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