fdsn_get_arrivals_by_id

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

Annotations already establish the tool as read-only, idempotent, and non-destructive. The description adds valuable behavioral context beyond that: the eventid is an opaque, provider-specific string that must not be invented or reformatted, and datacenter options (INGV, EMSC, GFZ, USGS, others). It also notes the output includes linked pick data, which is useful. This goes beyond the baseline, though it does not cover all edge cases like error handling.

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 appropriately concise, front-loaded with the core purpose, then usage guidance, a key warning about eventid, and datacenter options. Each sentence earns its place without redundancy. The structure guides the agent from what to when to how, with no wasted content.

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?

Given the tool's simplicity (2 parameters, output schema available, annotations covering safety), the description is complete. It covers purpose, usage conditions, parameter semantics, and datacenter choices. The critical eventid provenance requirement is essential for correct invocation and is clearly stated. No significant gaps remain for an agent to select and use the tool correctly.

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?

With a schema description coverage of 0%, the description fully compensates by explaining both parameters. For eventid, it clarifies its opaque nature, provenance from fdsn_query_earthquakes, and the strict requirement to copy verbatim. For datacenter, it lists valid options and the default (INGV), providing crucial meaning that the bare schema lacks.

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 identifies the tool's function: 'Get all seismic phase arrivals for an earthquake event, including linked pick data (station, time, phase).' It specifies the resource (seismic phase arrivals) and the action (get), and explicitly distinguishes this from sibling tools by focusing on arrivals and phase data. The use case is further clarified with examples like 'recorded phases, station readings, or seismic wave arrivals.'

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 states when to use the tool ('Use this when asked about recorded phases, station readings, or seismic wave arrivals') and provides a critical prerequisite: the eventid must be copied verbatim from a prior fdsn_query_earthquakes result. However, it does not explicitly mention when not to use it or contrast with sibling tools like fdsn_get_earthquake_by_id, so it misses the top score.

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