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

Annotations already cover read-only, idempotent, non-destructive, and closed-world behavior, so the bar is lower. Beyond them, the description discloses a genuinely useful trait: results are permission-filtered, and private spaces appear only 'if you have private access' — a conditional the agent could not infer from annotations alone.

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?

A single front-loaded colon construction that lists the inclusion criteria with zero filler. Every clause adds a distinct category or condition; nothing is repeated from the title or annotations.

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 tool with annotations and no output schema, the description covers what is included but not what a returned space looks like — no identifier shape, ordering, or indication of a default space. Since agents will likely need a space identifier for follow-up calls, that omission is a real but modest gap.

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 tool takes zero parameters and the schema is a closed empty object, so the baseline of 4 applies. The description does not need to explain inputs, and correctly spends none of its words on them.

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 names the resource (spaces) and precisely enumerates what the returned set comprises: owner's projects, General, member spaces, and conditionally private spaces. The list verb is implicit via the name/title, and no sibling is named for contrast, but an agent can tell this enumerates accessible spaces rather than threads or memory.

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 when-to-use statement, no prerequisite, and no mention of an alternative such as list_threads. The phrase 'Spaces you can read' only weakly implies it is a discovery call; nothing tells the agent whether to call it first, or how results feed into other tools.

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