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

Annotations already declare readOnlyHint=false, idempotentHint=false, destructiveHint=false, and openWorldHint=true, so the mutation/non-idempotent profile is covered. The description adds the useful 'Resolve chat_id independently from user_id' constraint, but says nothing about what happens when the user is already a participant, notification behavior, or permission requirements.

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?

The purpose is front-loaded in the first clause, which is good, but the remainder is a dense run-on that repeats schema content verbatim (chat_id definition, 'Never pass' lists) and mixes chat-ID and user-ID guidance without clear separation. It is informative but not tight.

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 a mutation tool, the description thoroughly covers identifier resolution but omits outcome behavior: success/failure semantics, idempotency effects, or what the caller gets back. Adequate for calling the tool, but incomplete for predicting its effects.

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 parameters are already documented in the schema — including much of the same 'Obtain with'/'Never pass' text that appears in the description (a notable duplication in chat_id). The description adds marginal value via the cross-ID resolution chain, so baseline 3 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?

States a specific verb+resource+scope: 'Add an exact provider user to an exact group chat.' An agent can immediately distinguish this from chat_remove_participant, chat_list_participants, and messaging_start_chat without opening a schema.

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 gives extensive guidance on how to obtain chat_id and user_id ('Obtain with: provider list conversations/inbox chats -> chat.id') and what never to pass, but it never states when this tool should be chosen over alternatives such as messaging_start_chat or messaging_send_message, nor any preconditions. Usage is implied rather than framed as a decision.

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