pix_get_custom_data

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

Annotations already establish readOnly, idempotent, non-destructive behavior. The description adds non-obvious behavior: results are time-ordered, kind filters event vs marker, and omitting data_type_id returns the fullest lane. This is useful beyond the structured hints.

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 sentences cover definition, motivation, and usage without repeating schema or annotations. The VSync explanation is slightly elaborate but earns its place by clarifying the tool's latency-analysis purpose.

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?

The description provides strong purpose and domain context and points to the discovery sibling. However, for an 8-parameter tool with no schema descriptions, omitting pagination/timeout/filter semantics leaves a material gap even though parameter titles give some hints.

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?

Only data_type_id and kind receive explanation; start_time, end_time, limit, cursor_position, and timeout_seconds are not described in the schema or the description. With 0% schema description coverage, the description needs to compensate for these parameters and does not.

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 first sentence states the exact deliverable: one custom data lane's events and markers in time order. It distinguishes the tool's scope from siblings like pix_list_custom_data_types, which enumerates available lanes/types rather than returning lane content.

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 monitor-lane/VSync example gives a concrete use case involving pix_get_gpu_frames, and the final sentence tells the agent to use pix_list_custom_data_types to discover available lanes. It lacks explicit when-not-to-use statements, but the context is clear.

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