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

Annotations already cover readOnlyHint=false and destructiveHint=false, so the description's mutation implication adds little. It does disclose the important behavioral rule 'Pass only fields explicitly requested' and warns against passing person/user IDs, which is useful context beyond structured data. However, it doesn't describe side effects, reversibility, permissions, or response 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?

The description is compact and front-loads the core action and key constraint ('Resolve chat_id first; do not use person/user ID'). The repeated chat_id block is a bit redundant with the schema but not wordy overall. Each sentence carries useful information, though the structure could be tightened by avoiding duplication.

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 two-parameter tool with no output schema and high schema coverage, the description covers the critical pitfalls (chat_id resolution, prohibiting user IDs, limiting to explicit fields). It is missing an account_id selection nuance (though the schema covers it) and doesn't clarify what 'mutable metadata' fields are supported, but these are minor given the simple signature.

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%, with chat_id and account_id both fully described in the schema. The description repeats the chat_id guidance verbatim but adds no new parameter-specific meaning beyond the schema. The 'Pass only fields explicitly requested' rule is a general usage guideline, not a parameter semantic, so it doesn't elevate the score above the schema-coverage baseline.

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 clearly states the verb 'Update' and the resource 'mutable metadata of an exact chat,' distinguishing it from sibling tools like chat_delete or chat_add_participant. The additional guidance on resolving chat_id clarifies the target but 'mutable metadata' remains somewhat broad, so it doesn't fully differentiate from messaging_set_chat_state.

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 provides explicit context: use only for exact chats, resolve chat_id first, never pass person/user IDs, and pass only explicitly requested fields. It gives concrete steps for obtaining the ID and strong do/don't guidance, but it doesn't name alternative tools or state when not to use it, so it stops short of full exclusionary guidance.

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