fdsn_get_focalmechanism_by_id

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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and destructiveHint=false, covering safety and idempotency. The description adds valuable behavioral context by noting that moment tensor data is returned 'when available' and that the eventid is opaque and must not be invented or reformatted—this is crucial for correct use beyond what annotations convey.

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 composed of four concise sentences, each adding unique value: purpose, return data, usage context, eventid caution, and datacenter options. There is no redundancy or filler, and the key information is front-loaded.

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 and the presence of annotations and output schema, the description covers the essential aspects: what it does, what it returns, prerequisites for eventid, and available datacenters. It doesn't detail error handling for invalid eventids, but that is a minor gap given the overall completeness.

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 description coverage is 0%, but the description compensates thoroughly. It explains that eventid is an opaque, provider-specific string that must be copied verbatim from a query result, which is essential guidance for the required parameter. It also lists valid datacenter options (INGV, EMSC, GFZ, USGS, etc.), giving meaningful semantics for the optional parameter.

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 'Get focal mechanism and moment tensor data for an earthquake event' and lists the specific outputs (nodal planes, principal axes, moment tensor components). This distinguishes it from sibling tools like fdsn_get_arrivals_by_id and fdsn_get_allmagnitudes_by_id, which cover other data types.

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 says 'Use this for understanding the rupture geometry and seismic source characteristics,' providing clear when-to-use context. It also mandates that the eventid must be copied verbatim from a prior fdsn_query_earthquakes result, which establishes a prerequisite and prevents misuse. However, it doesn't explicitly name alternative tools for other use cases.

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