Post an Instagram reel

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

The description adds substantial behavior beyond the annotations: reels can take a while to process, preview is non-mutating, polling can time out into a resumable in_progress state, and video constraints are only enforced by Instagram at fetch time. It also warns against duplicate posts when resuming. This is exactly the kind of behavioral nuance annotations alone cannot convey.

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 description is compact and front-loaded with the main operation, then covers preview semantics, resume flow, and validation caveats in just three sentences. Every sentence carries critical information with no filler or redundancy.

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 complex 9-parameter write tool with no output schema, the description covers the key edge cases: preview behavior, polling budget, resume semantics, and deferred validation. It does not describe what a successful final response looks like (e.g., published media ID or URL), which is a minor gap given no output schema is present, but the guidance is otherwise strong enough for an agent to use the tool correctly.

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%, so the schema already documents all nine parameters well. The description adds a little extra value by clarifying resumeContainerId's role in finishing an in_progress post and by noting videoUrl is validated only on Instagram fetch, but it largely reinforces what the schema already states.

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: 'Publish a reel in one call' and names the actual operation sequence (create REELS container, wait for processing, publish). It differentiates this tool from sibling tools by emphasizing the one-call reel flow vs lower-level container creation/publishing, and from image/story posts by resource type.

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 description gives clear context on when to actually write vs preview ('Preview performs nothing'), when to resume vs create new ('re-run with apply:true and resumeContainerId to finish... never create a new post'), and warns that validation happens on Instagram's side. It does not explicitly name sibling alternatives like instagram_create_media_container, but the one-call versus multi-step distinction is strongly implied.

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