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

Annotations already establish read-only and idempotent behavior. The description adds meaningful context by specifying 'static map context' and 'No live data is fetched', which is beyond the annotation hints. It does not contradict annotations, but could have added more about error conditions or response structure; however, the output schema covers the latter.

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 sized and front-loaded: the first sentence states the core purpose, followed by usage guidance, exclusions, and prerequisites. Every sentence contributes useful information without redundancy.

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 simple signature (one param, high schema coverage, and presence of an output schema), the description fully covers purpose, usage, exclusions, and prerequisites. It needs no further elaboration on return values because the output schema supplies that.

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 100% for the single parameter, and the schema already describes `stop_id` in detail. The description adds value by stating 'Requires a numeric stop ID' and providing a fallback instruction when only coordinates are available, which helps disambiguate how to obtain the required value.

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 the tool's action: 'Returns static map context for a stop: its marker and polylines for every route that serves it.' It also explicitly distinguishes itself from sibling `get_stop_realtime` by emphasizing 'No live data is fetched.'

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 explicit when-to-use and when-not-to-use guidance: 'Use this when you need to enrich an existing map with route shapes...' and 'Do NOT use this when live arrival times or vehicle positions are needed — use `get_stop_realtime` instead.' It also names a prerequisite for coordinate-based queries: 'call `get_stops_around_location` first if you only have coordinates.'

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