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

With no annotations provided, the description carries the disclosure burden. It clearly states the tool returns direct download URLs rather than a file and highlights the no-watermark behavior. It does not cover auth, error handling, or invalid-input behavior, but for a simple download tool this is reasonably transparent.

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 concise sentences each contribute useful information: the action, the output/no-watermark detail, and the input constraint with an example. There is no filler or repetition.

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 tool with one required parameter and no output schema, the description covers purpose, input requirements, an example, and the return value. It could mention what happens for invalid or non-video posts, but that is a minor gap given the tool's simplicity.

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 already documents the url parameter at 100% coverage, giving a baseline of 3. The description adds value by requiring that the post contain a video and by providing an example URL, which helps the agent understand the expected input format beyond the schema.

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 names a specific action (download), a specific resource (video from a Threads post URL), and the output type (direct video download URLs). It is clearly distinguishable from sibling tools, which focus on exports, profile reading, or post generation.

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 gives clear context for use: it applies when given a Threads post URL that contains a video, and it includes a concrete URL example. It does not explicitly list excluded cases or alternatives, so it falls short of a 5.

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