scratchjr_block_reference

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

Annotations already establish readOnlyHint=true and destructiveHint=false, and the description's 'Get' wording is consistent. The description adds that the tool returns a catalog of blocks, values, units, and guidance, but it does not disclose output format, structure, or any other behavioral traits. Given the annotations cover safety, this is adequate but not rich.

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 a single, front-loaded sentence that lists the key resources without excessive wording. The phrase 'project-building guidance' is slightly vague but does not add bloat or hinder quick parsing.

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 zero-parameter, read-only reference tool, this description is largely complete: it identifies the kind of information returned and is consistent with annotations. The main gap is the vagueness of 'guidance,' but an AI agent can still understand the tool's purpose and safe invocation without additional detail.

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?

The input schema has zero properties, so there are no parameters requiring semantic explanation. The description does not need to compensate for schema gaps, and the baseline for a no-parameter tool is appropriately high.

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 uses a specific verb ('Get') and names concrete resources: 'supported blocks, values, units and ScratchJr project-building guidance.' This distinguishes it from action-oriented siblings like create_project, run_project, or backup, though it does not explicitly call out a sibling comparison.

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?

There is no guidance on when to use this tool versus alternatives such as scratchjr_status, scratchjr_list_assets, or scratchjr_get_project. An agent must infer that this is a reference/lookup tool from the description, but no explicit context or exclusions are given.

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