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bizhawk_read16

Read a 16-bit little-endian value from emulator memory at a specified address. Use for game-state values like HP, score, or coordinates that occupy two bytes.

Instructions

PURPOSE: Read an unsigned 16-bit little-endian value from emulator memory at the given address. USAGE: Use for 16-bit fields (most game-state values: HP, score, coordinates). For single bytes use bizhawk_read8; for 32-bit values use bizhawk_read32; for non-aligned spans or big-endian fields use bizhawk_read_range and decode the bytes yourself (this tool always interprets bytes as little-endian regardless of the target system's native endianness). BEHAVIOR: No side effects — pure read. Reads two consecutive bytes (low byte at address, high byte at address+1) and combines them as little-endian. Returns an error if the named domain doesn't exist, address+2 exceeds domain size, or the core doesn't expose memory.read_u16_le. RETURNS: Single line 'ADDR_HEX: VAL_DEC (0xVAL_HEX)'.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
addressYesByte offset within the chosen memory domain. Per-domain offsets are 0-based and INDEPENDENT of system bus addresses (e.g. SNES WRAM uses 0x09C6, NOT 0x7E09C6). Reads 2 consecutive bytes starting here. Returns an error if address < 0 or address + 2 exceeds the domain's size.
domainNoOptional case-sensitive memory domain name. Omit to use BizHawk's currently selected domain (see bizhawk_get_info → current_memory_domain). Discover available names with bizhawk_list_memory_domains; they vary per system (WRAM on SNES, RAM on NES, RDRAM on N64, 68K RAM on Genesis, MainRAM on PSX, EWRAM/IWRAM on GBA). Returns an error if the name doesn't match any domain on the loaded core.
Behavior5/5

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

Despite no annotations, the description fully discloses behavioral traits: no side effects (pure read), byte ordering details (reads low byte at address, high byte at address+1, little-endian combination), and error conditions for missing domain, out-of-bounds, or missing core capability. This provides complete transparency for an agent.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Structured with bold headings for clear skimming. Every sentence is relevant, though slightly wordy. Could be shortened by removing redundant examples, but remains efficient for the information conveyed.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

No output schema, but description specifies exact return format. Covers all essential aspects: purpose, usage, behavior, errors, and integration with sibling tools. Complete for a simple read tool with two parameters.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Input schema has 100% coverage with detailed descriptions. The description adds value by explicitly stating the little-endian interpretation (not in schema) and the independence of bus addresses (already in schema but reinforced). A small but meaningful addition beyond schema.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

Description clearly states verb ('Read'), resource ('unsigned 16-bit little-endian value'), and context ('from emulator memory at the given address'). Distinguishes from siblings by explicitly naming alternatives (bizhawk_read8, bizhawk_read32, bizhawk_read_range) with specific use-cases, making the tool's purpose unmistakable.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Explicitly states when to use ('for 16-bit fields') and when not to use, listing exact sibling tools for other bit widths and endianness. Includes error conditions and domain selection guidance, leaving no ambiguity about appropriate invocation.

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

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