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

Annotations only supply destructiveHint=true; the description reinforces this with 'MUTATES Sendbird data' and adds two genuinely useful behavioral facts the annotations do not carry: file/multipart payloads are unsupported, and the operation maps to POST /{channel_type}/{channel_url}/messages. It stops short of auth requirements, rate limits, or error behavior.

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 tight sentences, front-loaded with the ALL-CAPS mutation flag, then the two send modes, then the exclusion and endpoint. No filler; every clause carries 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 an 11-parameter mutation tool with no output schema, the description covers the operation, the two modes, a key limitation, and the endpoint, while the schema fully documents parameters. Minor gaps remain around required permissions and what the response contains, but nothing essential to a correct call is missing.

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% and every parameter (user_id required for MESG, is_silent, send_push, mention_type, etc.) is already documented in the schema. The description's MESG/ADMM mention duplicates the message_type field description rather than adding new semantics, so the 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?

Names a specific verb and resource ('sends a message into a channel') and further qualifies the two modes (MESG as user, ADMM as admin) plus the underlying endpoint. This clearly separates it from the sibling read tools like sendbird_list_messages or sendbird_get_group_channel.

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?

Usage is implied by the mutation framing and the MESG/ADMM distinction, and one exclusion is given ('File/multipart messages are not supported'). However, it never states when to pick this tool over an alternative, nor does it point to any sibling for the unsupported file case, leaving the agent to infer.

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