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

Annotations already declare readOnlyHint/destructiveHint=false, so the safety profile is covered, and the description still adds a genuine operational gate: the phone must be video_live per list-phones-tool. It also discloses a cost/robustness trait (cheaper than an image), which is real behavioral context beyond the annotations. Return metadata like resolution is not discussed, but width is controllable via schema.

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?

Three short sentences, zero filler, with the action and mechanism front-loaded and the prerequisite placed last where it is easy to check. Nothing is repeated for its own sake.

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 2-parameter read tool with a 100%-covered schema and annotations carrying the safety profile, the description covers action, prerequisite, and relative cost, and notes the return is OCR text. Only marginal gaps remain (e.g., no mention of OCR failure/empty-text behavior), which is acceptable given no output schema exists.

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%, so both parameters (slot, width) are fully documented in the schema itself, including the UUID-vs-display-name rule and the video_live constraint. The description only restates the video_live prerequisite and adds no new parameter syntax or format detail. Baseline 3 applies.

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 — 'Read the on-screen text of a farm phone' — and immediately describes the mechanism ('snapshots the slot and returns the OCR-recognized text'). The clause 'cheaper than an image when you only need the text' implicitly separates it from phone-snapshot-tool, so an agent can distinguish the two without opening schemas.

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?

Gives a clear selection condition versus the imaging sibling ('cheaper than an image when you only need the text') and states a hard prerequisite ('The phone must show video_live: true in list-phones-tool'). It never names phone-snapshot-tool explicitly, so the alternative is inferred rather than spelled out.

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