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

Annotations already declare the safety profile (readOnlyHint=false, idempotentHint=false, destructiveHint=false), so the bar is lower. The description adds the append semantics and the mandatory pre-read step, which is useful behavioral context, but says nothing about failure modes, duplicate blocks, or how the mutation affects existing script content.

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?

Two tight sentences, zero filler, with the core action front-loaded and the prerequisite immediately following. Every sentence earns its place.

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?

No output schema exists, so return values need not be explained, and the guide reference is a reasonable strategy for the unguessable vocabulary. However, for a 29-parameter mutation tool, deferring essentially all parameter meaning to an external resource leaves the description thin relative to the tool's complexity.

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 only 3% across 29 parameters, so the description carries the burden — yet it explains no individual parameter. It does acknowledge that block type names, section names, and piping rules are unguessable and points to the authoring guide, which is a partial mitigation for the `type`/`section` params, but the vast majority of parameters remain semantically opaque.

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 gives a specific verb and resource ('Append one block to a project's script'), which cleanly separates it from update_block, delete_block, and replace_script by the 'append' action. It stops short of naming any sibling explicitly, so a reader must infer the distinction, keeping it at a 4 rather than a 5.

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 states a clear prerequisite — read the subo://guide/authoring resource before writing — and explains why (block types, section names, and piping rules are unguessable). That is solid when-to-use context, but there is no guidance on when to prefer this over replace_script, plan_script, or generate_script, so no exclusions are offered.

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