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

Adds non-obvious behavior beyond the readOnlyHint annotations: data comes from ShortSync's cached inbox sync and no platform API call occurs on read, which lets an agent reason about staleness and latency. It doesn't state how stale the cache may be or whether a sync_inbox call is needed to refresh, so not a 5.

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 short sentences: purpose and ordering first, then the usage pointer, then the caching caveat. Every sentence carries distinct information with zero repetition.

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 should hint at what a message looks like and whether there's pagination; it does say results are ordered oldest-first so the tail is newest, but doesn't say if there's a has_more cursor beyond limit. Adequate for a small read tool but slightly incomplete.

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 limit/default/max and workspace_id auto-resolution are already documented. The description only repeats the oldest-first ordering and adds no new parameter guidance, which is the baseline 3.

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 ('Returns') and resource ('messages in an inbox conversation') with a scope qualifier (oldest-first). This clearly separates it from list_inbox_conversations, which returns conversations rather than their messages, and the schema's conversation_id description reinforces the chain.

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 says to call it 'before reply_to_comment when you need thread context', naming both the sibling and the condition. It lacks an explicit when-not (e.g., don't use for a single message, or when live data is required), so it falls just short of 5.

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