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

Annotations already declare readOnlyHint=true and destructiveHint=false, so safety is covered. The description adds that the result includes the full media set and that the lookup is by two identifiers, which is useful behavioral context beyond the annotations. It does not address not-found behavior, but that is minor for a simple read-only getter.

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?

One clean, front-loaded sentence states the resource, payload, and lookup key without wasted words. Every phrase contributes meaning.

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?

For a two-parameter read-only getter, this description is nearly complete: it names the compound key and promises the full media set. There is no output schema, so slightly more detail on empty or missing results would round it out, but an agent can invoke it confidently in most cases.

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 carry parameter meaning. It tells the agent that source and external id together form the key, which is helpful, but it does not define valid sourceKey values or externalId format. The parameter names still do most of the work.

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 uses a specific verb ('fetch'), a precise resource ('one sighting record'), and distinguishes itself with 'full media set' and the compound lookup key ('source and external id'). This clearly separates it from siblings like search_sightings or get_news.

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 condition for use is implied clearly: call this when you have the source and external id and need a single sighting with its media. It does not explicitly name alternatives or exclusions, but the compound key makes the appropriate context obvious.

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