render_preview

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

Beyond the readOnlyHint/openWorldHint annotations, it discloses that the default capture includes live state machines and that `parameters` overrides apply only to this frame, which is genuinely useful behavioral context. It says nothing about width handling, revision conflicts, or session scoping, but the additions it does make are substantive.

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, front-loaded with the core action, and each sentence carries information about defaults or behavior. The slash-separated parameter list is compact rather than padded, though it reads slightly telegraphic.

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 read-only render tool with no output schema, the description covers the key semantic choices (live vs. deterministic, frame-local overrides). However, with four of seven parameters undocumented and no mention of the returned image encoding or size, an agent still has gaps.

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 0% across 7 parameters, so the description must carry the load. It explains timeMs, timelineIds, and the frame-local nature of parameters well, but width, sessionId, requestId, and expectedRevision are left entirely undefined.

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 opens with a concrete verb+resource: "Return an actual PNG frame." The word "actual" implicitly contrasts it with evaluate_frame-style numeric evaluation, but it never names a sibling, so the differentiation is inferable rather than explicit.

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?

It clearly states two usage modes: no arguments captures the current live state including state machines, and timelineIds yields deterministic time-based previews. That is a real when-to-use rule. It stops short of naming alternatives or exclusions (e.g., when to prefer evaluate_frame or export_svg).

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