threads_list_replies

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

Goes well past readOnlyHint=true by disclosing the required scope (threads_read_replies plus access to the post), the pagination invariant ('null means no more pages', plus the edge case where an empty items list still carries a next_cursor), and an explicit prompt-injection warning about reply text. That is substantive behavioral context the annotations cannot convey.

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 action, then prerequisites, then the two non-obvious behaviors (recursion and pagination), then the safety note. Multi-line but every sentence carries distinct information with no restatement of the name or schema.

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 read-only listing tool with an output schema, the description covers everything an agent needs: auth requirements, ID sourcing, recursion strategy, pagination termination rule, and content-trust handling. The only omission, the limit bound, is available in the schema itself.

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 0%, so the description must carry the load; it explains the provenance and format of account_id and post_id and clarifies that next_cursor is passed as 'after'. The 'limit' parameter (default 20, max 100) is never mentioned, leaving one of four parameters undocumented in both schema and description.

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 with explicit scope: 'Read one page of direct replies under a Threads post or reply.' The qualifiers 'one page' and 'direct replies' pre-empt confusion with conversation/thread traversal and with pending-reply moderation siblings.

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?

Gives prerequisite sourcing for both required IDs ('Get account_id from threads_list_accounts and post_id from threads_list_posts'), states the permission needed, and explains exactly how to descend into nested replies via has_replies and how to continue paging via next_cursor.

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