Frame breakdown

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

Annotations only supply readOnlyHint=true, so the description carries most of the burden and does so well: it defines ordering (oldest first), the meaning of each timing field, that steps>1 indicates catch-up, and that longTaskMs is browser-reported main-thread stall. The headless-mode caveat is a genuinely non-obvious behavioral trait. It stops short of covering pagination/limits or cost.

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 tightly packed sentences with zero filler: the return shape and field semantics lead, then the usage hint and the headless caveat close. Every clause carries information an agent needs.

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?

There is no output schema, so the description must explain return values, and it names and interprets every reported field, plus the headless-mode semantic caveat. For a read-only diagnostic tool with one well-documented parameter, nothing material is missing.

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 single 'count' parameter has 100% schema description coverage ('Default 60'), so the schema already documents it. The description never mentions count, its default, or the 240 cap, adding no meaning beyond the schema. Baseline 3 applies when the schema does the heavy lifting.

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 makes clear this returns recent per-frame timing data ('Recent frames, oldest first') and enumerates exactly which fields come back, so an agent knows the resource and granularity. It does not explicitly contrast itself with close siblings like game_profile or game_state, but the frame-level scope is distinct enough to route correctly.

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?

'Use it to explain stutter' gives a concrete when-to-use context that an agent can act on. It adds a meaningful when-not caveat ('in headless mode times reflect stepping, not real play'), though it names no explicit alternative tool for profiling vs. frame inspection.

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