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

Annotations already declare readOnly/idempotent/non-destructive/closed-world, so the safety profile is covered; the description goes beyond that by enumerating the returned row fields, disclosing the 'Media not found' failure outcome, and warning that the content is untrusted user-generated input. It omits auth/rate-limit expectations, so it is strong but not exhaustive.

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 sentences, front-loaded with the verb+resource, then the exact identifier location, then the return shape and the trust caveat. The field enumeration does work that a missing output schema would otherwise force the agent to guess, so nothing is padding.

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 returned columns and the not-found sentinel, and it covers the single required parameter and the untrusted-content handling. Nothing an agent needs to call this read tool correctly is missing.

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 100%, so the baseline is 3, but the description adds real meaning: the shortcode is the segment after instagram.com/p/ or /reel/, and it is the same value exposed as `code` in list results. That cross-reference to sibling output is the kind of detail the schema field does not carry.

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?

States a specific verb and resource ('Get one Instagram post or reel by its shortcode') and pins the identifier down to the exact path segment, which separates it from the surrounding list tools (get_user_medias, get_top_medias) and from the TikTok equivalents (get_tt_media_by_id). An agent can tell exactly what this retrieves without opening the schema.

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?

Explicitly scopes usage with 'Use it for full details of a single post' and ties the input to the `code` field returned by list results, so the agent knows when this is the right follow-up call. It does not name an alternative or state when-not to use it, which keeps it short of a 5.

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