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

Annotations only give the safety profile (non-read-only, non-destructive, non-idempotent). The description adds genuinely new behavioral context: free-plan exports carry a MockClip watermark, the free plan is limited to 2 MCP renders, and callers on the free plan should be told about /pricing. It still says nothing about render latency or how the result is delivered.

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 one dense block of prose with no headings or ordering; critical routing facts (per-screen payload shapes, thread view, compose behavior) are buried mid-paragraph. Nearly every sentence is informative, but the wall-of-text format makes it hard to scan for the relevant clause.

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 23-parameter, deeply nested, no-output-schema render tool, the description covers the high-value semantics (feeds, thread, compose, screens, flow, account) plus plan limits. Less central params (theme, soundSettings, showTaps behaviors beyond the default note) are left to the schema, which is a reasonable division.

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 only 35% across 23 params, so the description has to carry weight, and it does: it explains `script` step semantics (scroll/like/repost/newPosts/reply/pause, offset, top/bottom), that each `reply` step reveals the next `pendingReplies` item, that `composedPost` lands on top of the first feed once the flow leaves compose, that `newPostsLabel` uses `{n}` as the count placeholder, and that `account` is shared across profile header and side menu. This meaningfully exceeds the bare 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?

Opens with a specific verb+resource ("Create a X feed animation") and then enumerates the concrete surfaces it renders (post cards, thread view, compose screen, flow). Against siblings like create_reddit_thread and create_instagram_dm_conversation, the X-feed scope is unambiguous from the name plus first clause alone.

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 explains how to drive each screen (feed screens take `posts`+`script`, thread view takes `post:{...}`, other screens take rows by screen id) which is effectively usage guidance for constructing a call. It stops short of explicit when-not guidance, though app-specific tooling makes the sibling choice self-evident.

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