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

With no annotations provided, the description carries the full burden and does well: it discloses normalization behavior (scaling/letterboxing to a single size), the default sizing rule (first clip's size), and an audio-tolerance behavior (silent track injected for clips lacking audio, guaranteeing an audio stream). It stops short of disclosing failure modes, input source expectations, or what the tool returns.

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 short sentences, zero filler, and the most important fact (what the tool produces) leads. Each sentence contributes a distinct, non-redundant piece of information.

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 3-parameter tool with no annotations and no output schema, the description covers the transformation behavior well but leaves the return value entirely unstated — an agent cannot tell whether it receives a URL, a file handle, or a job id. Input-source expectations for the URLs are also unaddressed, which matters for a media-merge operation.

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 compensate. It gives real meaning to width/height ('the first clip's size unless width/height are given'), which effectively explains the default-0 sentinel, but it never explains the `urls` array beyond the 2-10 count — no URL format, no ordering statement — nor whether width and height must be supplied together or how aspect ratios are reconciled.

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?

States a specific verb ('Join'), resource ('videos'), the ordering semantics ('end to end'), the output format ('one MP4'), and an operational bound ('2-10'). This is distinguishable at a glance from siblings like video_trim, video_speed, or video_convert, which each alter rather than merge a single clip.

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 2-10 clip constraint implicitly bounds when the tool is applicable, and 'join end to end' implies the merging use case. However, there is no explicit when-to-use versus alternatives, no statement about prerequisites (e.g., clip compatibility, hosted vs local URLs), and no when-not guidance.

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