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

Annotations already declare readOnlyHint and openWorldHint, yet the description adds real value: it discloses that the tool falls back to the public embed payload when the web client's persisted query is unavailable, that play counts are included in the same request, and that it costs 1 credit. These are meaningful behavioral details beyond the structured 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?

The core purpose 'Post or reel details' is front-loaded, followed by return fields, then behavioral notes. Four sentences are dense but each contributes (scope, fallback behavior, play-count note, cost), with no filler.

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 compensates by listing the return payload fields (caption, media URLs, engagement counts) and explaining the fallback and credit cost. The only gap is the unexplained cache_max_age parameter, which is minor for a read-only single-post 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 coverage is 50%: url is documented in the schema and reinforced implicitly ('one public post, reel or carousel'), while cache_max_age is undocumented in both schema and description. The description adds marginal value (e.g., 'no play-count parameter to pass') but does not compensate for the uncovered cache_max_age parameter.

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 description names a specific verb+resource ('Post or reel details') and enumerates the returned fields (caption, media URLs, engagement counts), so an agent knows exactly what it fetches. It doesn't explicitly distinguish itself from siblings like instagram_userPosts or instagram_reelsSearch, but the single-post focus is clear.

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 phrase 'One public post, reel or carousel' implies it is for single-post lookups and the URL/shortcode input is implied, but there is no explicit when-to-use or when-not-to-use guidance versus sibling tools such as instagram_userPosts or instagram_profile. Usage is inferable rather than stated.

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