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

Annotations only say readOnlyHint=false and destructiveHint=false; the description goes well beyond by disclosing the concrete side effects: unread counts decrement across every open screen, and pending push notifications and letters are not sent. The monotonic constraint 'Never moves backwards' is a non-obvious behavioral guarantee an agent could not get from the schema.

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 dense sentence with the core action front-loaded, followed by the effect and then the constraint. The em-dash aside carries the upTo default without a separate clause; no sentence 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?

For a two-parameter mutation with no output schema and minimal annotation coverage, the description supplies the missing behavioral picture (side effects, notification suppression, monotonicity). Only an explicit pointer to the read/listing siblings would add meaningful value.

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 coverage is 100%, so both parameters are already documented, including upTo's default of the newest message. The description's restatement of that default adds little beyond the schema, though 'never moves backwards' hints that upTo beyond the current read point is a no-op.

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 names a specific verb+resource ('read a chat up to a message') and describes the effect in concrete terms (unread count drops, notifications suppressed). It does not explicitly distinguish itself from related siblings such as get_chat_messages or mark_wiki_page_read, but the operation is unambiguous.

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 conditional framing 'Say you have read a chat up to a message' and the analogy to opening it on screen, but no sibling or alternative is named, and there is no explicit when-not-to-use guidance. An agent can infer the context but must do the work itself.

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