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

Annotations already declare read-only, idempotent, non-destructive behavior, and the description adds materially: hard area caps per source (2x2 km IGN, 20x20 km Sentinel-2), the least-cloudy-scene selection rule with default 60-day/20% cloud window, return format and CRS, embedded licence, and the non-obvious quirk that 'download links build their file when opened; no file is saved'. The instruction never to pass those links to open_gis_file is exactly the kind of cross-tool caveat only a description can carry.

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?

Front-loaded with the use case, then constraints, with zero filler sentences — every clause carries a decision rule. It is a single dense paragraph with semicolon-chained clauses, which makes it slightly harder to scan than a short bulleted structure would be.

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?

Covers selection logic, geographic and size limits, defaults, scene-picking behavior, output format and CRS, and edge-case exclusions — everything an agent needs to choose between sources and avoid misuse. With an output schema present, it correctly does not spend words on return-value structure beyond the GeoTIFF/preview note.

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 100%, so the schema already documents every parameter including defaults and enums; the description nonetheless adds meaning the schema lacks, notably the area-size limits tied to each source and the default-source decision rule. It does not add syntax detail for date/bbox formats beyond the schema, so it stays just above baseline.

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?

States a specific verb and resource (retrieve a satellite/aerial image of an area as a file for QGIS) and enumerates the product variants (true colour, false colour, NDVI). It clearly separates itself from siblings by naming the file-consumer (QGIS) and the things it is not (street-level photos, weather, explanations of NDVI).

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?

Explicitly states when to use it, when not to ('Not for street-level photos, live weather or a picture more recent than a few days; to explain what NDVI or a band is, answer without this tool'), and gives routing rules between the two sources including which is the default in which geography and product combination. It even gives an alternative action (answer directly) instead of calling a tool.

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