# Tool details
The tool table lives in the [README](../README.md#tools). This covers the behavior behind it.
## Core tools
Always registered: `read_file`, `write_file`, `edit_file`, `apply_patch`, `delete_file`,
`create_directory`, `execute_command`, `memory`, `agent`, the checklist trio (`task_create`,
`task_update`, `task_list`), `ask_user_question`, and the context pair (`context_archive`,
`compact_context`, below).
`web_search` and `web_fetch` register when their backend is viable (below); MCP tools when a
server is configured.
Editing: `edit_file` is for one location -- `target_content` must match once (or set
`allow_multiple`), with matching that degrades in steps from exact through trailing-whitespace,
full-trim and Unicode normalisation before refusing. `apply_patch` is for multi-hunk and
new-file work and takes a unified diff, range headers included. Both write atomically beneath
the resolved root, snapshot a checkpoint for `/undo`, and replay through the approval queue.
Paths outside the project (absolute, or traversing out of it) resolve to where they point and
are gated as external access: `read_only` denies, `ask` prompts with a per-directory
"don't ask again", `auto` classifies, `full_access` allows. See the README's [Safety](../README.md#safety) section.
## Context tools
Compaction summarizes older history out of the working context, but nothing is deleted: every
message stays in the session's `.mermaid/conversations/<id>.jsonl` log. `context_archive`
searches that log (case-insensitive `query`), reads any message back whole (`message`, paged
with `char_offset` past 32,000 characters), or lists it. Messages are numbered in the order they
happened and marked with the compaction that removed them, so the checkpoint summary is never
the only copy of anything.
`compact_context` lets the model checkpoint when it judges its context noisy, with an optional
`focus` for the handoff; it runs before the model's next call. The automatic trigger
(`[compaction] auto_threshold_percent`, 85% by default) stays as the safety net. On a provider
that compacts server-side (Anthropic), the provider handles that automatic trigger instead
(`[compaction] provider_native`); `compact_context` and `/compact` still run Mermaid's own.
## MCP tools
MCP servers contribute additional tools under the `mcp__<server>__<tool>` prefix when configured. Names and schemas are sanitized to provider-safe form at startup (charset `[A-Za-z0-9_-]`, 64-char cap, `$ref` inlining and other schema normalization); `enabled_tools`/`disabled_tools` filters keep matching the RAW tool names the server itself advertises.
Servers start concurrently at launch, each bounded by a 60-second timeout, and report ready/errored individually.
By default MCP tools are **deferred**: instead of advertising every server's tools on every request, the model gets one `tool_search` tool that searches deferred tool names/descriptions and promotes matches to direct advertisement for the rest of the session — deferred schemas don't count against `/context` until promoted. Opt out globally with `mcp_defer_tools = false` at the top level of config, or per server with `defer = false` on its `[mcp_servers.<name>]` entry.
## Web tools
`web_fetch` is registered natively with no key. `web_search` is registered when the selected backend is viable; the managed default is omitted with an actionable diagnostic on unsupported platforms.
HTML is reduced to its main content by a readability pass. When that guesses wrong (a table,
a nav-hosted index, attribute data), `raw: true` returns the page source as served instead;
it needs the native fetch backend.
Inspect an existing `web_fetch` snapshot with Unicode-caseless `pattern` matching, or page through it with stable `start_line`/`line_count` continuation, without refetching.
Backend selection, redirect and provenance rules, and the transfer budgets are in
[configuration.md](configuration.md#web-tool-backends).
## Inline approvals
In `ask` mode — and on an `auto` escalation — a gated action pauses and prompts inline
(`1` Yes · `2` Yes, don't ask again · `3`/Esc No). The agent waits for your answer instead of
erroring out.