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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint, so "Read-only: returns public data and changes nothing" largely restates structured data. It does add two useful pieces of context beyond annotations: that only public data is reachable (implying private accounts will not resolve) and the cost of 1 credit per request. It says nothing about error behavior or whether failed lookups still consume a credit.

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?

Three short sentences, front-loaded with the verb+resource, followed by safety and cost. No filler, no repetition of the title beyond the identifying clause, and the most decision-relevant constraint (cost) is near the front.

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 single-parameter read tool with full schema coverage and complete annotations, this is close to adequate, but with no output schema the description gives no hint about what "post details" includes (caption, media, metrics, timestamp) or how private/deleted posts surface. The credit-cost claim also raises an unresolved question about charging on failure.

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 100%, and the schema itself already explains that the parameter accepts a bare shortcode or a full post/Reel URL with examples. The description's "by shortcode" adds no format, URL-parsing, or validation detail beyond that, so the baseline of 3 applies.

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 states a specific verb and resource ("Get post details by shortcode"), which is unambiguous about what is returned. It does not explicitly differentiate itself from nearby siblings like instagram_user_posts or instagram_post_comments, but the shortcode-keyed lookup is distinguishable from those by name 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?

There is no statement of when to use this tool versus alternatives such as instagram_user_posts (listing a user's posts) or instagram_post_comments. No prerequisites, no guidance on what to do if the shortcode is private or invalid, and no mention of whether other tools accept the same shortcode.

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