Context limits

Context limits control how much text fx loads from instructions, skills, MCP tools, and image analysis. If content is shortened or omitted, press ctrl+o to see the limit notice in Full detail.

Available limits

Field	Description	Default
`skill_description_bytes`	Each skill's description in the catalog	1 KiB
`skill_catalog_bytes`	Combined skill catalog	Based on the model's context window
`skill_chunk_bytes`	Skill content returned by one read	Whole file
`skill_file_bytes`	Each skill file or reference file	1 MiB
`mcp_description_bytes`	Each MCP tool description in search results	1 KiB
`mcp_search_result_bytes`	Combined MCP tool search results	16 KiB
`mcp_server_instructions_bytes`	Instructions from each MCP server	2 KiB
`mcp_selected_schema_bytes`	One tool's schema, or the combined schemas loaded by a search	64 KiB
`project_instruction_file_bytes`	Each instruction file	64 KiB
`project_instructions_total_bytes`	Combined project instructions	128 KiB
`image_adapter_output_bytes`	Text returned by the vision tool	20 KiB

The skill catalog budget is estimated from 2% of the model's context window, using four bytes per token. If the context size is unknown, it defaults to 8,000 characters. Setting skill_catalog_bytes replaces this with a fixed byte limit.

Skills load as complete files. If a file exceeds skill_file_bytes or an explicit skill_chunk_bytes limit, fx rejects the load instead of returning partial instructions.

Settings

Add context_limits to ~/.fx/settings.json. This example doubles the per-file and combined instruction limits:

{
  "context_limits": {
    "project_instruction_file_bytes": 131072,
    "project_instructions_total_bytes": 262144
  }
}

Use a non-negative integer in bytes, or "off" to disable a limit. All values, including "off", are capped at 64 MiB.

You can also set limits in a workspace entry. Restart fx after editing the file. Project .fx.json does not accept context_limits.

Command-line overrides

Place --context-limit before the command to override a limit for one run:

$fx --context-limit project_instruction_file_bytes=131072

Repeat the flag to change more than one limit:

$fx --context-limit project_instruction_file_bytes=off --context-limit project_instructions_total_bytes=off

Command-line values override workspace and global settings.