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

Annotations already establish that this is a safe, non-open-world read (readOnlyHint=true, openWorldHint=false). The description adds useful behavior beyond that: the payload includes per-account publish status and media, and in app-capable hosts the result is rendered as an interactive panel with an explicit instruction not to duplicate it as text. That is meaningful context not derivable from the 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?

Two sentences, front-loaded with the core purpose. The second sentence is dense but each clause earns its place by telling the agent how to handle rendered output; no filler or repetition of the title.

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 steps in to name the return contents (publish status, media) and the host-dependent rendering, so an agent knows what to expect. It stops short of covering failure cases such as an unknown or deleted post id, a minor gap for a simple read.

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?

There is a single required parameter (postId) with 0% schema description coverage, so the description must carry the meaning. 'Fetch one post by id' tells the agent the parameter identifies a post, which is adequate but adds no format, source, or retrieval detail beyond the obvious.

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 with scope: 'Fetch one post by id'. The singular 'one post' and 'by id' clearly distinguish it from the plural list_posts sibling, and the mention of per-account publish status and media sharpens what is returned.

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?

Usage is implied rather than stated: an agent can infer this is the single-item counterpart to list_posts, but no alternative or condition is named explicitly. The only real guidance concerns how to present the result in app-capable hosts, not when to choose this tool.

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