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

readOnlyHint=true already covers the safety profile, so the description earns credit for adding operational context instead: the required reactions:read scope and the reconnect hint for workspaces connected before 2026-08-28. It also discloses the return shape (per-emoji name, count, and reacting user ids), which matters because no output schema exists.

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?

A single front-loaded sentence stating verb, resource, scope and return contents, followed by one short permission caveat. No filler; every clause earns its place.

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 usefully enumerates the returned fields, and it discloses the required scope and the reconnect caveat. It stops short of mentioning pagination or behavior when a message has no reactions, which are minor gaps for this tool.

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% (channel, ts, account all documented), so the schema already carries parameter meaning and the baseline is 3. The description adds only the implicit 'one message' framing and nothing about the account label or composite external_id handling.

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 ('List'), resource ('emoji reactions'), and scope ('on one Slack message') plus the exact contents returned (name, count, user ids). This clearly separates it from list_my_reactions (which is caller-scoped) and from add_reaction/remove_reaction, which mutate.

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 phrase 'on one Slack message' implies the usage context (looking up the breakdown of an existing message's reactions) and implicitly contrasts with list_my_reactions, but no explicit when-to-use/when-not guidance or named alternative is given. Usage is inferred rather than stated.

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