tools-mermaid-render

Render mermaid diagrams from a Markdown file (or a lone .mmd) to standalone SVGs for reuse in articles. Extracts each ```mermaid block (pure, tested) and drives a render engine (mmdc) with a strict argument vector — no shell. Engine is used only as an offline DOM->SVG renderer of our own HTML, never to control a live site (that stays the bridge's job).

Tier	tools
Role	unclassified (baselined)
Path	`crates/tools/mermaid-render`
Edition	2021
Targets	tools-mermaid-render, tools_mermaid_render, render_live
Public items	12 across 0 modules
Tests	13

What it is for

tools-mermaid-render — extract mermaid diagrams from Markdown and name their output SVGs. This library is the PURE half: block extraction, slugging, output naming. The subprocess render lives in main.rs.

Deliberate scope limits (operator, 2026-08-08):

SVG only. There is no format parameter anywhere. The tool cannot emit

PNG/PDF, so it cannot be talked into a different output.

Not an agent-arbitrary capability. The CLI surface is two paths in

(input file, output dir) and SVG files out. It takes no URL, no shell, no pass-through flags, so it cannot be repurposed to control a browser. The render engine (mmdc/puppeteer) is used ONLY as an offline DOM→SVG renderer of our own generated HTML; live-site control stays the bridge's job. Invoke it from the /diagram skill or by hand, never as a free tool a model reaches for.

Capabilities

`crate root`

tools-mermaid-render — extract mermaid diagrams from Markdown and name their

Item
`pub const MAX_INPUT_BYTES: u64`
`pub const MAX_SVG_BYTES: usize`
`pub const RENDER_TIMEOUT: std::time::Duration`
`pub const RENDERER_VERSION: & str`
`fn puppeteer_config(dir : & std::path::Path) -> anyhow::Result <Option <std::path::PathBuf>>`
`fn render_to_svg(source : & str, work_dir : & std::path::Path) -> anyhow::Result <String>`
`fn slugify(s : & str) -> String`
`fn output_name(stem : & str, index : usize, heading : Option <& str>) -> String`

`Block`

tools-mermaid-render — extract mermaid diagrams from Markdown and name their

Item
`pub const MAX_BLOCK_BYTES: usize`
`pub const MAX_BLOCKS: usize`
`pub struct Block`
`fn extract_blocks(md : & str) -> Vec <Block>`

How to use it

No examples/ target and no doctest in this crate's rustdoc. The tests listed under Verification are the closest executable usage.

Module structure

No public modules: the crate root is its whole surface.

Public surface

`crate root`

Item	What it is
`pub const MAX_INPUT_BYTES: u64`	Cap on the Markdown input we will read (bytes)
`pub const MAX_BLOCK_BYTES: usize`	Cap on one block's mermaid source (bytes)
`pub const MAX_SVG_BYTES: usize`	Cap on an SVG accepted back from the renderer (bytes)
`pub const RENDER_TIMEOUT: std::time::Duration`	Wall-clock cap for one block
`pub const RENDERER_VERSION: & str`	The renderer's identity, stored beside each SVG so a mermaid upgrade that changes output is visible as a version difference rather than a silent redraw.
`fn puppeteer_config(dir : & std::path::Path) -> anyhow::Result <Option <std::path::PathBuf>>`	Resolve a Puppeteer config so `mmdc` reuses the system Chrome instead of downloading its own
`fn render_to_svg(source : & str, work_dir : & std::path::Path) -> anyhow::Result <String>`	Render one mermaid source to SVG text, using `work_dir` for the transient source and output files
`pub const MAX_BLOCKS: usize`	Cap on diagrams per file
`pub struct Block`	One extracted diagram: the nearest preceding heading (for naming) and the mermaid source between the fences.
`fn extract_blocks(md : & str) -> Vec <Block>`	Extract every `mermaid fenced block from Markdown, in document order
`fn slugify(s : & str) -> String`	Lowercase kebab slug: alphanumerics kept, every run of other chars becomes a single `-`, trimmed
`fn output_name(stem : & str, index : usize, heading : Option <& str>) -> String`	Output filename for block `index` (0-based) of a file whose stem is `stem`

No pub use re-exports: every item above is declared in this crate.

Boundary

Depends on no other workspace tier.

Shares tier tools with 84 other crates: tools-advisory-reach, tools-archive-guard, tools-artifact-scaffold, tools-ask-ai-core, tools-ask-ais, tools-ask-gemini, tools-book, tools-book-report, … (84 total).

_What this crate deliberately does NOT own is a judgment. No committed registry records one for it, so none is stated here._

Where it sits

Tier (ontology)	`tools`
Architectural role (taxonomy)	`unclassified (baselined)`
Location	`crates/tools/mermaid-render`
Vocabulary in force (lexicon)	`current`

Dependencies

Runtime, from outside the workspace.

Crate	Requirement	Features	Optional	Only on
`anyhow`	`^1`	—	no	always

Development. None.

Build. None.

Depended on by. 1 workspace crate.

Signal flow — what reaches this crate, and what it reaches.

flowchart LR
  n_tools_corpus["tools-corpus"] -->|uses| SELF
  SELF["tools-mermaid-render"]
  classDef self fill:#1f883d,stroke:#1f883d,color:#fff;
  class SELF self;

Feature flags

No Cargo features are defined: every capability is unconditional, so no consumer can receive a half-wired crate.

Targets

Kind	Name	Source
bin	`tools-mermaid-render`	`src/main.rs`
lib	`tools_mermaid_render`	`src/lib.rs`
test	`render_live`	`tests/render_live.rs`

Error model

No public error type was detected: no public item declares a type named *Error, and no public signature returns one.

Operational characteristics

Property	Evidence
async public surface	none detected
async runtime	none detected
database access	none detected
network I/O	none detected
unsafe code	none detected
environment variables	yes

No unsafe block, unsafe fn, unsafe impl or unsafe trait was found by the parser anywhere in this crate's source.

Configuration

Variable	Read in
`MERMAID_MMDC`	`src/lib.rs`
`MERMAID_PUPPETEER_CONFIG`	`src/lib.rs`

1 workspace crate depends on this one: tools-corpus.

Verification

Kind	Count
Unit tests	9
Integration tests	4
Examples	0
Doctests	0

Evidence by module. How often each public module is named by something executable.

Module	Tests	Examples	Consumers
`crate root`	12	0	5

What the tests establish, by name:

a_flowchart_renders_to_svg — tests/render_live.rs
a_source_over_the_cap_is_refused_without_spawning_anything — tests/render_live.rs
an_empty_source_is_refused_without_spawning_anything — tests/render_live.rs
source_that_is_not_a_diagram_is_refused_rather_than_stored — tests/render_live.rs
extracts_blocks_in_order_with_nearest_heading — src/lib.rs
heading_section_numbers_are_stripped — src/lib.rs
non_mermaid_fences_are_ignored — src/lib.rs
output_names_are_indexed_and_slugged — src/lib.rs
slugify_is_kebab_and_never_empty — src/lib.rs
both_flags_parse_in_either_order — src/main.rs
help_flags_detected_and_nothing_else — src/main.rs
missing_either_flag_is_an_error — src/main.rs
unknown_flag_is_rejected — src/main.rs

Documentation coverage

Measure	Documented	Total
Public items with rustdoc	12	12
Public modules with a `//!` block	0	0

pie showData
    title Public items with rustdoc
    "Documented" : 12
    "No rustdoc detected" : 0

Metrics

Metric	Value
Rust source files	2
Source lines	622
Code lines	468
Public API items	12
Public modules	0
Tests	13
Examples	0
Cargo features	0
Direct runtime dependencies	1
Workspace reverse dependencies	1

pie showData
    title Public API by kind
    "constant" : 6
    "function" : 5
    "struct" : 1

pie showData
    title Rust source composition
    "Code" : 468
    "Blank or comment" : 154

Generation

Rendered by tools-corpus corpus readme from repository evidence alone, renderer schema 2, lexicon current. No model, network service or database was consulted. Regenerate with tools-corpus corpus readme --write; verify with --check.