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

Annotations already cover the safety profile (readOnlyHint=true, destructiveHint=false, openWorldHint=false), so "Read-only. Does not write files" is largely redundant. The description earns credit by disclosing behavior annotations can't: auth resolution differences between org and public extensions, and how to interpret the `requirementsMd` field. No pagination or error behavior is mentioned.

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 purpose in the first sentence, and the rest is dense with actionable detail rather than filler. It is on the long side because return-field semantics and the build-vs-embed workflow are interleaved, but each clause carries information.

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?

With no output schema, the description appropriately compensates by naming the surface fields and explaining the meaning of `requirementsMd`, plus credential handling. It is nearly complete for a small read tool; only pagination/volume expectations are unstated.

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 coverage is 100% and both parameters are already documented in the schema, including that extensionId is "the `id` from a list_extensions result" and hubToken is a JWT fallback. The description's "Pass the extension's id from list_extensions" repeats that verbatim and adds nothing, so baseline 3 applies.

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?

Specific verb+resource+scope: "List the SURFACES an extension exposes — embeddable iframe injection points." It enumerates the returned fields (surfaceId, platform, type, url), which distinguishes it clearly from sibling read tools like hub_get_extension_surfaces or flow_list_extension_custom_tables.

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?

Explicit routing guidance: pass the id "from list_extensions," and a decision rule for results — prefer building natively when `requirementsMd` is present, embed `<ExtensionSurface>` only when it's absent, grounding via lookup_engine_component. It also names both credential paths (own hub extension vs public marketplace), which is exactly the when/how an agent needs.

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