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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds one real behavioral constraint (input codec/resolution/frame-rate compatibility), but says nothing about output form, input size limits, or processing cost, which matters for a video merge.

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?

It is a single sentence and the operative constraint is placed at the end with an em-dash, which is reasonably front-loaded. The 'client and server side from freedailypro' clause is filler that consumes attention without informing the call.

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 and no return-format annotation, the agent cannot tell what comes back from a merge (a base64 video string? a URL?). The description covers the key compatibility constraint but is silent on output, which is a meaningful gap for a transform 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% for the single parameter filesBase64, so the description carries the burden. It conveys only 'multiple videos' (implying an array of >=2) and never states that inputs must be base64-encoded strings, leaving the parameter format undocumented everywhere.

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 and resource ('merge multiple videos into one'), which is unambiguous against the mostly audio/pdf/image siblings. It does not explicitly differentiate from nearby tools like video_convert or video_trim, and the trailing phrase 'client and server side from freedailypro' adds branding noise rather than clarity.

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 precondition 'requires matching codec/resolution/frame rate across inputs' is genuine usage guidance — it tells the agent when this call will fail. However, there is no explicit when-to-use vs alternatives (e.g., video_convert for format changes) and no statement of when not to use it.

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