reply_to_post

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

The description discloses mutation and non-idempotency, explicitly noting 'each call adds a new comment', which goes beyond the annotations. It also adds credential requirements, the thing-id format needed for parent identification, the return value, and a warning about spam detection—all valuable behavioral context beyond what annotations provide.

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 front-loaded with the core purpose and each subsequent sentence carries meaningful operational or safety information. Despite being longer than minimal, there is no filler; every sentence earns its place by covering credentials, reply mechanics, alternatives, and a spam-detection warning.

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 mutating tool with no output schema, the description is unusually complete: it states the return value, explains parent-id formats for both posts and comments, gives the authentication requirement, and warns about rate limiting. This gives the agent enough context to select, invoke, and interpret the result 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 description coverage is 100%, so the schema already documents post_id and content thoroughly. The description reinforces the t3_/t1_ prefix semantics and the nesting behavior, but it does not add substantial new parameter-level details beyond what the input schema already states.

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 opens with 'Post a reply to an existing post or comment', using a specific verb and resource that clearly defines the action. It also distinguishes itself from siblings like create_post and edit_comment by explicitly mentioning top-level and nested replies and referencing edit_comment as the alternative for changing an existing reply.

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?

It explicitly says 'Use edit_comment to change a reply you already posted', giving a direct alternative. It also clarifies when to use this tool (for both top-level and nested replies) and warns about spam detection and REDDIT_SAFE_MODE, which helps the agent decide when and how to invoke it.

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