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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, yet the description still adds substantive behavior: moderation can hide reels that are still counted in totals, coverage is limited to already-tracked authors, no author creation or metric refresh happens, and enumeration continues via next_cursor. These are exactly the operational surprises an agent needs to know.

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 front-loaded with the selection rationale, then moves cleanly through parameters, return fields, and caveats with no filler sentences. The only minor waste is the trailing 'Read-only.' which merely restates the annotation, and the parameter prose is packed densely enough to require careful reading.

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 supplies the return shape itself (link, published_at, duration, views and read time, x_factor, is_trending, library-analysis presence). Combined with pagination and moderation semantics, an agent has everything needed to call this correctly and to reason about the results.

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 carries the full burden and does: platform values and the same-name-different-author rule, accepted handle formats (@name, name, profile link), filter semantics including what 'trending' means, inclusive UTC semantics for the date bounds, the 1-50 range and default for limit, and the cursor/next_cursor continuation contract.

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 opening sentence names a specific verb and resource with scope: 'the stored history of one author on one platform: their trending and ordinary reels.' That scoping implicitly separates it from siblings like trending_videos (cross-author) and get_author_baseline (aggregate), and the trailing caveat 'never adds an author or refreshes metrics' rules out the write-ish interpretations an agent might otherwise consider.

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 an explicit triggering condition ('Use this when you need the stored history of one author... to compare a viral reel with the author's usual ones') and an implicit exclusion ('Only covers authors ViralDecoder already tracks; never adds an author or refreshes metrics'). What's missing is naming a concrete alternative — e.g. when to prefer get_author_baseline or trending_videos instead.

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