set_post_body

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

With no annotations, the description carries the transparency burden. It discloses the replacing/destructive nature, the result verification behavior ('reports how many nodes of each type were stored'), and a key constraint ('An image must already be hosted by Substack'). It does not mention permissions, rate limits, or what happens to an existing body, but those are not expected in every description.

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?

Five sentences, each carrying distinct value: purpose, uniqueness + content types, prerequisite workflow, result verification, and image constraint. No filler, front-loaded with the core action.

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 tool with a very complex nested ProseMirror schema and no output schema, the description covers the essential selection and invocation context: what it replaces, why it is unique, the prerequisite, the verification result, and a critical input constraint. It omits explicit error/return details, but given the schema's exhaustive structure, this is a strong, complete description.

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 baseline is 3. The description adds the image-hosting constraint and the create_draft_post prerequisite, but these largely echo or lightly augment the schema's own notes (e.g., draft_id 'as returned by list_posts or create_draft_post'). It does not add substantial meaning beyond the highly detailed schema.

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?

Uses a specific verb-resource pair: 'replace the body of a draft with a Substack document.' It explicitly differentiates from siblings by stating it is 'the only way to write structured content' and enumerates the supported node types (headings, lists, links, code blocks, images, buttons, paywall).

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 an explicit workflow: 'Create the draft first with create_draft_post, then call this with its id.' The phrase 'the only way to write structured content' signals when to prefer it over alternatives like update_draft. However, it does not explicitly name update_draft as the alternative for non-structured edits, so it falls just short of a 5.

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