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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=false. The description adds valuable behavioral context beyond these flags by specifying that only locally-cached messages are searched and that no network access is required. This clarifies the tool's data scope and offline nature, which is not covered by the annotations.

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 exactly two sentences, with no filler. The first sentence states the core purpose, and the second adds a critical constraint. Information is front-loaded and every phrase earns its place, making it highly efficient for an AI agent to parse.

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?

Given the presence of an output schema and strong annotations, the description is nearly complete. It covers the tool's purpose, local-only scope, and optional chat_id restriction. The only minor gap is not mentioning that the search is case-insensitive or the default limit, but these are already documented in the input schema, so the context is adequate.

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 100% coverage, describing all three parameters (limit, query, chat_id) with clear descriptions. The tool's description only restates the chat_id restriction in prose, adding no extra semantic details beyond what the schema already provides. Therefore, the description meets the baseline but does not elevate parameter understanding.

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 opens with a specific verb and resource: 'Full-text search across locally-cached Signal messages.' It clearly identifies the platform (Signal), the scope (locally-cached), and the operation (full-text search). This distinguishes it from sibling search tools like slack_search_messages or teams_search_messages, which target different platforms.

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 provides clear context: this tool searches messages that Signal Desktop has stored on disk, with no network access. It implies the tool is appropriate when the user wants to search local Signal messages, but it does not explicitly name alternatives or state when not to use it. Thus it gives clear context without explicit exclusions.

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