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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, so the bar for adding behavioral disclosures is lower. The description adds non-obvious context about scope visibility (anonymous IP, BYO key hash, account ID) and the conditional behavior of omitting the key to list all saved keys. This goes beyond what annotations provide, though it doesn't mention error cases or return format.

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 two sentences. The first sentence states the core functionality and listing option; the second frame the use case and relationship to siblings. Every sentence carries weight with no fluff, and it's front-loaded with the verb and resource.

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 simple tool with one optional parameter and no output schema, the description is complete. It covers what the tool does, how to invoke both modes, scope, and its place in the tool family. No significant gaps remain.

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 schema already covers the 'key' parameter thoroughly (100% coverage), so baseline is 3. The description adds extra meaning by giving concrete examples of what keys represent (target ticker, address, research notes) and explicitly states the omit-to-list behavior, which reinforces the schema's description and helps the agent understand what values are expected.

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 ('Retrieve') and clearly distinguishes the tool from siblings by explaining both retrieval of a specific saved value and listing all keys. It also clarifies scope ('Scoped to your identifier'), which sharpens the purpose.

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?

The description explicitly states when to use the tool ('Use to look up context the agent stored earlier') and gives concrete examples of what to look up. It also names sibling tools and their roles ('Pair with remember to save, forget to delete'), providing clear guidance on alternatives.

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