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

The description discloses meaningful behavior beyond annotations: nothing is stored, read-back never keeps the file, usage is billed as one read, and the first five per month are free. It also explains return semantics (every form box with value and filled status, plus labels/completeness when recognized). The annotations show idempotentHint=true, which is consistent with 'nothing is stored', and readOnlyHint=false is reasonably explained by billing.

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?

Three tightly packed sentences front-load the core purpose, then input requirements, then returns, then retention/billing. Every sentence carries essential information and there is no filler or repetition.

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-style tool with 3 optional parameters, the description covers input format, output shape, optional-parameter purpose, data retention, and pricing. With an output schema available to define return types, nothing essential is missing for an agent to decide and invoke this tool correctly.

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 0%, so the description carries the full burden. It covers all three parameters: pdf_url as a public https link, pdf_base64 as an alternative, and form_id as an optional contextual input that upgrades the output with labels and completeness. This adds substantial meaning beyond the bare schema.

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: 'Read the values out of a filled PDF form', and immediately adds distinctive outcomes: labeling by field, required-status, and a completeness verdict. This separates it clearly from siblings like get_form, verify_form, or inspect_pdf.

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 gives clear input instructions ('Give the filled PDF... and, when you know it, form_id') and explains when the optional form_id matters for richer output. However, it never explicitly contrasts this tool with alternatives or states when to prefer it over sibling tools such as verify_form or inspect_pdf, leaving usage selection partly implied.

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