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

Annotations only declare readOnlyHint=false and destructiveHint=false, leaving the real behavior to the description. It adds substantial rules beyond them: no duplicate reaction, system messages take no reactions, reactions are keyed by the reacting user, and only Kosmodrom web reactions are supported.

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?

Front-loads the add/remove purpose and then packs the constraints efficiently. It is a single long compound sentence rather than cleanly separated, but every clause earns its place and none is wasted.

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 and full annotation coverage of only the safety flags, the description supplies the edge cases (duplicate suppression, system-message exclusion, keying by user) an agent needs. It could go slightly further on remove-specific behavior, but is largely complete.

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 the schema already documents all three parameters, including the full reaction enum meanings that the description merely points to ('meanings in reaction'). The description adds little parameter-level detail beyond the schema, so baseline 3 applies.

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 (adds/removes), resource (the token owner's reaction), and target (a chat message). It clearly distinguishes itself from chat_send/chat_message_update by being the textless-reaction tool.

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?

Explains the appropriate context for a reaction (a textless reply when the meaning is unambiguous) with concrete examples. It stops short of naming alternative siblings (e.g. chat_send) or giving explicit when-not-to-use conditions, so it is strong but not exhaustive.

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