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

Annotations already declare readOnlyHint, idempotentHint, and non-destructive, and the description adds substantial behavior beyond that: omission of not-found IDs, a database-first-then-parallel-external-API fetch strategy, caching semantics with forceLatest cost caveats, and trial-mode constraints (up to 5 cached database-only results, never triggers live fetching). It also confirms the safety profile ('safe, read-only tool'), which is fully consistent with the annotations.

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?

Tool-specific content is tightly front-loaded: purpose, behavior, usage, performance benefits, and the critical format warning all appear in the first sentences. The trailing RIAL ACCESS block is disproportionately long and mostly platform-level boilerplate that repeats across tools — though it does carry the tool-specific trial limit of 5 cached results — so not every sentence earns its place.

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?

Given there is no output schema, the description supplies the return shape (results array with id, caption, userId, username, createdAtDate, engagement metrics, count, dataSource). It covers selection criteria, ID formatting, URL resolution, caching and performance trade-offs, and auth requirements — everything an agent needs to invoke this 8-parameter tool correctly is present.

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?

With 63% schema coverage, the description compensates for the key gaps: it explains the strong_id format with a concrete example and the critical cross-tool warning to use the full 'id' value rather than the media_id, gives concrete fields parameter examples, and documents trial token acquisition and Bearer usage. Internal parameters like _isTrial and _requestId remain undocumented directly, though the lengthy trial section covers their surrounding context.

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 and resource — 'Get multiple Instagram posts by IDs (1-50 IDs per request)' — establishing exact scope and limits up front. The explicit 'NOT for search - use getInstagramPostsByKeywords' differentiates it from the closest sibling, and the ID-based scope also separates it from getInstagramPostsByUser and the other platforms' by-IDs tools.

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?

States the explicit trigger condition ('Use when you have multiple exact post IDs'), an explicit exclusion ('NOT for search - use getInstagramPostsByKeywords'), and a fallback procedure for Instagram URLs: extract the shortcode and search, or ask the user for the post ID. An agent gets a complete decision procedure with named alternatives and needs no inference.

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