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

With no annotations, the description carries the full burden, and it adds valuable traits: immediate return, shared numbering across the room, and an explicit security warning to treat results as untrusted input. It does not clarify whether calling read updates the 'last read' cursor, which is a minor but relevant behavioral gap.

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 sentences, each doing essential work: core purpose and numbering, immediate-return contrast with wait, and security caution. No filler, and the key action is front-loaded.

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 zero-parameter read operation, the description covers what is returned (numbered messages since last read), behavior (immediate), and safety (untrusted input). The output schema is absent, but the description gives enough to use the tool correctly and interpret results.

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?

The tool has zero parameters and schema coverage is 100%, so the schema already fully documents the input. The description adds no parameter detail because none is needed; it instead explains the return semantics, which is appropriate.

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 opens with a specific verb and resource: 'Return messages posted since this chat last read, numbered.' This clearly distinguishes the tool from siblings like 'say' (send), 'wait' (hold for reply), and 'search' (query history), so an agent knows exactly what it does.

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 explicitly contrasts with 'wait': 'Returns immediately; use wait when you expect a reply and want to hold for it.' This gives a direct when-to-use and when-not-to-use condition, and the alternative is named.

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