Gemini document understanding

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

Annotations already declare readOnlyHint=true and destructiveHint=false. The description adds useful behavioral context: the server does not reclassify the source, and local paths are resolved on the MCP server. This complements the annotations without contradicting them.

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, front-loads the purpose ('Understand one document source'), and includes only essential details about modality selection and source resolution. No fluff or redundancy.

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 read-only tool with no output schema, the description and schema sufficiently cover the input source, prompt, and optional MIME hint. It does not describe the return format, but the prompt's schema (determine/extract/summarize) implies a text response, so the overall picture is complete.

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 description coverage is 100%, so the schema already documents all three parameters. The description restates source types (URL/path) but adds no new parameter-specific semantics beyond what the schema provides, earning the baseline 3.

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 the specific verb 'understand' and resource 'document source', enumerates example types (PDF, CSV, text) and source kinds (URL or local path). It also differentiates from sibling tools by stating the caller chooses the document modality, making its scope unambiguous.

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?

It clearly scopes the tool to document sources and implies that other modalities have dedicated tools. However, it does not explicitly name alternative tools or state 'use web for URLs to web pages', so it stops short of fully explicit when-not-to-use guidance.

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