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

Beyond the readOnlyHint/idempotentHint annotations, it discloses the return payload (a stored JPEG, up to 3 MB, delivered as image content) along with its timestamp or slide number, and it defines the access scope (the account's own analyses and every shared library card). It also flags a behavioral exception — Threads analyses return no frames. The trailing "Read-only" merely restates the annotation, which is the only redundancy.

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?

The trigger condition is front-loaded in the first clause, and each subsequent sentence carries distinct information (parameters, return payload, scope, exception). The opening sentence is dense with parentheticals, but nothing is genuinely redundant apart from "Read-only."

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 no output schema, the description still tells the agent exactly what comes back (image content plus timestamp/slide number) and its size ceiling, which is what an agent needs before committing to an image-returning call. Combined with the parameter sourcing and the Threads exclusion, nothing material is missing for a 3-parameter read 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?

Schema description coverage is 0%, so the description must carry the burden, and it explains the provenance of ref_type/ref_id (from search_library or get_reference_analysis) and where frame_index values come from (the part=frames listing). It does not define the enum values job vs library_reel or state whether frame_index is zero- or one-based, leaving small gaps for a 3-parameter tool.

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?

"Use this when you need to see an actual frame of an analyzed video (or a slide of a carousel), not only its text description" states a concrete verb (fetch a stored frame image) and resource, and explicitly contrasts with text-only siblings like get_analysis. An agent can distinguish it from search_library or analysis_card purely from this sentence.

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 gives both the trigger condition and the alternatives: use this when text description is insufficient, and for Threads post analyses use get_analysis instead because they have no frames. It also tells the agent where the parameters come from (search_library, get_reference_analysis, and a frame list obtained with part=frames).

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