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

With no annotations provided, the description carries the behavioral burden and does substantial work: returns one MediaItem, no picker/table, throws not_found, and pipes mediaId downstream. It could go further by stating explicitly that the operation is read-only and what happens if the account is invalid, but it is still well beyond minimum.

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?

Dense, front-loaded, and purposeful. The primary purpose appears first, and every sentence adds information about routing, return shape, errors, filters, or downstream usage, 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?

The description covers purpose, routing, return shape, errors, and downstream integration, which is strong given no annotations and no output schema. It is slightly incomplete because accountId semantics are missing and the MediaItem structure is only implied via mediaId.

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 schema description coverage is 0%, so the description must explain all parameters. It explains mediaType well, including its enum values and narrowing behavior, but accountId is never explained, including whether it selects the live account, whether it is required, or what its default is.

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 clearly identifies the operation: resolving exactly one most recent published media item for a singular user intent. It also distinguishes itself from siblings like list_scheduled_posts and list_published_media, so an agent can distinguish without inspecting schemas.

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 states when to use this tool (singular live-account intent, flow triggers) and when not (bare 'my most recent post' with no platform cue → list_scheduled_posts; browsing multiple → list_published_media). This gives the agent concrete routing rules.

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