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

Annotations already declare readOnlyHint and openWorldHint, so the bar is lower; the description still adds real behavioral context: ordering (newest first), returned fields (favourite/reply/boost counts), a content exclusion (boosts), and a cost signal ('Costs 1 credit'). It does not mention caching behavior despite a cache_max_age parameter.

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?

Four short sentences, front-loaded with the resource, then return contents, then exclusion, then cost. No filler; each sentence carries distinct information.

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 simple read tool with annotations covering safety and no output schema, the description adequately covers return contents, ordering, exclusions and cost. The remaining gap is parameter-level guidance (notably count, cache_max_age, and the odd string type of exclude_replies).

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 only 60%: count and cache_max_age have no descriptions, and the description says nothing about count, cursor, cache_max_age or the string-typed exclude_replies. For a 5-parameter tool with partial schema documentation, the description should compensate but adds no parameter meaning at all.

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+resource ('An account's public posts, newest first') and scopes it further by naming the fields returned and excluding boosts of other people's posts. That scope implicitly separates it from mastodon_post (single post), mastodon_postReplies and mastodon_profile, though no sibling is named explicitly.

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 implies when to use it (to read an account's timeline) and gives one exclusion (boosts are omitted), but offers no explicit when-to-use/when-not guidance or pointers to alternatives such as mastodon_profile or mastodon_postReplies.

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