fetch_inbox

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

Annotations (readOnlyHint=false, destructiveHint=false) are consistent with the description, which adds real side-effect context: mark_read defaults to true, so it flips read state, and 'include_bodies adds body_md' / 'mark_read:false' for preview. It also gives the pagination termination rule ('Stop when fewer than limit messages return') and the filter-combination caveat, none of which appear in annotations.

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?

Front-loaded with the core return statement, then usage, then pagination, then alternatives. Very dense and every sentence carries information, though the middle section packs defaults and filter caveats into long clauses that slightly strain readability.

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 10 parameters, no output schema, and read-write side effects, the description covers the return shape (metadata entries and the sender_t3_thread field), pagination, defaults, and the alternatives. An agent has everything needed to call it correctly.

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 the baseline is 3, but the description adds semantics the schema lacks: pagination loop behavior, the interaction between include_bodies and mark_read defaults, that filters combine, and what sender_t3_thread means ('null outside T3'). It adds genuine value beyond the field descriptions.

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 and resource: 'Return an array of your latest received message metadata, newest first.' It also names sibling tools for adjacent jobs (search_messages, mark_message_read, acknowledge_message), but it never distinguishes itself from fetch_session_inbox, the closest sibling, leaving that boundary ambiguous.

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?

Explicit when-to-use with concrete parameter recipes: 'At session start or after a mail notice, set unread_only:true, include_bodies:true and mark_read:true.' It also states exclusions and alternatives: 'Use search_messages for project-wide text matching, or mark_message_read or acknowledge_message for one message.' Nothing is left to inference.

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