start_session

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

Annotations declare readOnlyHint=false, openWorldHint=true, idempotentHint=false, destructiveHint=false. The description adds beyond annotations the performance benefit (10-50x faster), the scrcpy-server dependency, and that starting a session is a stateful operation (implicit via 'session is active'). This adds meaningful behavioral context.

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?

Two sentences that are efficient and front-loaded with the core purpose. The first sentence states the primary function and benefit; the second adds a critical prerequisite. Minimal waste, though the performance claim (10-50x) is slightly verbose but informative.

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?

With a full output schema, 100% parameter coverage, and detailed annotations, the description's job is largely done. It covers the key value proposition (speed gain), the prerequisite, and clearly explains what starting the session enables. Complete enough for an agent to correctly decide when to invoke this tool.

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?

The schema description coverage is 100%, so all three parameters (maxFps, serial, maxSize) are documented in the schema with defaults and ranges. The description adds no additional parameter detail beyond what the schema already provides, so baseline 3 is appropriate. The description mentions none of the parameters explicitly.

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 verb+resource: 'Start a scrcpy session for fast input control and screenshots.' It explicitly distinguishes from siblings like start_video_stream by referencing scrcpy and naming the specific operations (tap/swipe/text/screenshot) that become faster. The performance benefit (10-50x) adds concrete differentiation.

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 explains when to use it (when faster input control and screenshots are desired) and notes the prerequisite 'Requires scrcpy-server to be installed.' While it doesn't explicitly name stop_session as the counterpart, the clear pairing with stop_session is implied and the prerequisite condition provides practical guidance.

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