PurRAssist black cat holding a repaired structure

PurRAssist

Assistance for AIs that get the details almost right.

PurRAssist recovers intent from imperfect JSON, names, paths, and text. Give a decoder a schema and an effort level: it searches composed corrections, validates the complete result, and returns evidence of what changed. A schema-valid guess is still a guess. Ambiguous alternatives remain visible. Use it as a Rust crate, an MCP server, or a CLI.

Version 0.1.0. Published as rust-v0.1.0: the six crates are on crates.io, with documentation on docs.rs. Read the changelog, the implementation contract for the accepted scope, and the qualification record for executable evidence. Its known limitations are not release blockers. The release procedure records the package and registry gates.

One engine, three interfaces

One recovery engine, three equal ways to use it: as a Rust crate, as an MCP server, and as a command-line tool. They share the same engines and the same evidence receipts.

Rust crate

cargo add purrassist

use purrassist::{Outcome, RecoveryRequest, Schema};

let schema = Schema::compile(r#"{
  "type": "object",
  "required": ["temperature"],
  "properties": {"temperature": {"type": "number"}},
  "additionalProperties": false
}"#)?;

let answer = schema.recover("[[{temperatur: '42',}]]", RecoveryRequest::default());
match answer.outcome {
    Outcome::Resolved(value) => assert_eq!(value.to_json(), r#"{"temperature":42}"#),
    Outcome::BestGuess(value) => println!("inferred: {}", value.to_json()),
    Outcome::Ambiguous(values) => println!("{} interpretations", values.len()),
    Outcome::Unresolved => println!("{}", answer.receipt.stopped),
}
# Ok::<(), purrassist::schema::SchemaError>(())

The purrassist crate is the Rust interface: it re-exports the pure engines, the syntax integration and the derives.

MCP server

cargo install purrassist-cli
purrassist mcp --root /path/to/workspace

Add the server to any MCP client that launches stdio servers:

{
  "mcpServers": {
    "purrassist": {
      "command": "purrassist",
      "args": ["mcp", "--root", "/path/to/workspace"]
    }
  }
}

The server speaks newline-delimited JSON-RPC over stdio. Every tool is listed in the tool reference. Starting the server creates a .purrassist/ directory in the root, where the file tools keep their transaction journals; the call command below does the same.

CLI

purrassist decode --schema schema.json --input response.txt
purrassist call match_strings --root DIR < args.json

purrassist call TOOL --root DIR reads a JSON argument object from stdin and invokes the same operation used by MCP: for every registered tool the CLI and MCP results are identical, which the test every_registry_entry_has_a_fixture_validated_through_cli_and_mcp checks tool by tool. The convenience commands decode and match are shortcuts with their own output, not the tools' output. purrassist validate prints exactly the validate_json tool's output.

Crate map

Six crates make up the release set, published in this order:

Two workspace crates are internal and not published: wasm-harness (native, WASI and browser-WASM acceptance transcripts) and purrassist-helper-census (the duplicate-functionality census).

Capabilities

The pure core owns its JSON parser, exact decimal arithmetic, schema validator, Unicode normalization, edit distances, phonetic matching, semantic rules, recovery search, and receipts. It has zero third-party runtime dependencies. The isolated syntax crate uses the pinned Tree-sitter grammar family; see the dependency inventory. Each tool is described in the tool reference.

Current surfaces include:

• JSON recovery with nested unwrapping, syntax repair, approximate keys/enums, stringified values, whole-schema validation, and invented values (required properties, patternProperties/additionalProperties/dependentSchemas fills, propertyNames-conformant key repairs) produced by a first-party witness-generation algebra rather than a schema-blind heuristic.
• Unicode, lexical, Levenshtein, unrestricted Damerau-Levenshtein, English Soundex, aliases, and contextual path matching.
• Explicit semantic domain rules and caller-supplied embedding similarity.
• Source-bound text edits, bounded fuzzy replacement, relocatable unified diffs, overlap checks, exact-byte undo, and a Markdown editing index and structural section/list/table/reference operations. All 1,324 pinned CommonMark/GFM examples have exact rendering checks, alongside generated preservation properties and independent differential campaigns.
• Python, Rust, JavaScript/JSX, TypeScript/TSX grammar inspection and validated punctuation repairs. Grammar acceptance does not prove program correctness.
• Journaled single-file replacement and conditional undo for coordinated writers.
• Tool-call recovery from raw model output: weighted, invertible dialect grammars with best-first markup repair, resolution against typed tools or lossless OpenAI/MCP/Anthropic declarations (Draft 2020-12 or Draft-07 schemas), per-call outcomes with itemized repairs, conservative guards for mutating tools, and re-emission as any dialect or the OpenAI tool_calls array. Call markup of a dialect that is not built in yet, or not in the request's allow-list, is reported as a rejected attempt (unsupported_dialect), never silent content. Twelve dialects ship: qwen3-coder-xml.v1, hermes.v1, openai-tool-calls.v1, llama3-json.v1, mistral-v3.v1, mistral-v11.v1, deepseek-v3.1.v1, deepseek-v3.v1, kimi-k2.v1, anthropic-tool-use.v1, harmony.v1, and bare-json.v1; callers add their own with the grammar DSL. Typed tool definitions derive from Rust structs and enums with #[derive(ToolDefinition)] and #[derive(ToolEnum)] (the zero-dependency purrassist-derive crate, re-exported by the facade; see the example below). Still tracked: the pythonic.v1 (#12), glm-4.5.v1 (#13) and gemma3-tool-code.v1 (#14) dialects, the *-stripped variants (#18), streaming recognition (#16), and provider streaming events (#17). See tool-call recovery.
• CLI, stdio MCP, and resumable helper request/response adapters (prepare_helper and complete_helper; see helpers). No model is required, loaded, or contacted by default.

A tool's schema and its typed arguments can come from one Rust struct:

use purrassist::json;
use purrassist::tool_call::{FromNode, ToolArguments};

#[derive(purrassist::ToolEnum, Debug, PartialEq)]
enum Order {
    Asc,
    Desc,
}

/// Search the index.
#[derive(purrassist::ToolDefinition, Debug, PartialEq)]
#[tool(effects = read_only)]
struct Search {
    /// What to look for.
    query: String,
    #[param(default = 10)]
    limit: u32,
    order: Option<Order>,
}

assert_eq!(Search::tool_definition().name(), "search");
let arguments = json::parse(r#"{"query": "cats", "order": "Desc"}"#)?;
assert_eq!(
    Search::from_node(&arguments),
    Ok(Search { query: "cats".into(), limit: 10, order: Some(Order::Desc) }),
);
# Ok::<(), Box<dyn std::error::Error>>(())

Schema::generate_witness/generate_witness_governed separately implement a witness-generation algebra (canonicalize, eliminate not by De Morgan duality, merge allOf constraints, and generate a type-directed value, recursing over $ref/$dynamicRef): its result is a validated Witness, a closed-form Unsatisfiable proof (never inferred from search exhaustion), or an honest Exhausted, and recovery invents every guessed value through this same algebra. Schema::compile_governed and with_resources_governed return typed CompilationError values separating invalid schemas from resource failures. Pass the same governor to recover_governed to share the total preparation and recovery budget. The decode_json tool does this automatically. The convenience compilation methods use the default finite budget.

purrassist_core::patch::Patch (an ordered, non-overlapping, source-digest- bound set of byte-range replacements) is the crate's single edit representation; edits::EditPlan/TextEdit are aliases for it. Beyond apply, it exposes a governed invert, compose, commute, rebase, and diff algebra; apply_edit/apply_file use rebase/diff to reconcile a stale plan against an intervening change through an explicit rebase_from input. See plan application. The Rust markdown::Document API's structural operations — insert_section, remove_section, move_section (with optional re-leveling of the moved section's own heading), rename_heading, ListItemEdit::Move, renumber_list, TableRowEdit::Move, TableColumnEdit::Move, and add_reference/relabel_reference/remove_reference/unlink_reference (which rewrite every shortcut/collapsed/full-reference use resolving to the affected definition) — are exposed through the host tool plan_markdown_structure, selected by a typed op (section_insert, section_remove, section_move, section_rename, list_move, list_renumber, table_row_move, table_column_move, reference_add, reference_relabel, reference_remove, reference_unlink). Each is governed, digest-bound, reparse-checked, and provides an exact inverse.

The Rust markdown::InlineFragment layer retains exact byte spans and renders code spans, emphasis, strong emphasis, inline links/images, escapes, line breaks, autolinks, and raw inline HTML. Explicit dialect selection preserves the pinned CommonMark/GFM rendering differences. Named/numeric entities are decoded. markdown::References collects definitions from supplied paragraph blocks; InlineFragment::parse_with_references resolves full, collapsed, and shortcut links/images while retaining definition provenance. Document::render_html collects definitions across containers and renders blocks. GFM rendering enables tables, task lists, strikethrough, extended autolinks, and tag filtering; explicit extension profiles are also available. All 1,324 pinned official document examples match exact HTML under their upstream profiles. Generated adversarial preservation and independent differential checks extend this finite corpus; the qualification record states their coverage and limits.

File tools reject stale versions and record transaction identities for undo. The portable filesystem layer coordinates cooperating writers; it is not a sandbox against malicious directory replacement or an atomic multi-file transaction.

Governed engines and host tools accept caller-owned cancellation, with explicit transaction boundaries. The stdio MCP server handles cancellation while tools run and admits at most four active tool calls.

Use the checkout

cargo run -p purrassist-cli -- --help
cargo run -p purrassist-cli -- match raeder reader writer
cargo run -p purrassist-cli -- call match_strings --root . < examples/match-strings.json
cargo run -p purrassist-cli -- call resolve_string --root . < examples/resolve-string.json
cargo run -p purrassist-cli -- decode --schema examples/temperature.schema.json \
  --input examples/temperature.input.txt
cargo run -p purrassist-cli -- recover-tool-calls --tools tools.json --emit openai turn.txt
cargo run -p purrassist-cli -- mcp --root /path/to/workspace

decode returns the answer and receipt as JSON. Exact performs no recovery; Quick, Standard, Deep, and Maximum increase finite search budgets. Exhaustion is explicit and never proves that a schema is unsatisfiable. recover-tool-calls prints the same result as the recover_tool_calls MCP tool and never executes a call. Every example request under examples/ is run through both the CLI and MCP by the test suite. The tool reference describes each tool, its arguments, and its example; the integration guide lists every recover-tool-calls option.

Develop and verify

Rust edition 2024, MSRV 1.98. Development uses nightly Rust with Clippy and rustfmt. No commit-verification bypass is permitted.

make check       # formatting, attribution/dependencies, lint, optimized tests, docs
make wasm-test   # compare native/WASI recovery, matching, embeddings, Markdown, and grammars
make syntax-oracles  # compare fixed syntax probes to independent compilers
make benchmark  # recovery quality assertions and latency baseline
make fuzz       # ten coverage-guided targets and independent pattern/Markdown oracles
make fuzz-hosted  # the CI and pre-tag fuzz gate (known #6/#11 limitations handled)
make resources  # allocations, heap/RSS, latency, artifact size, and uncached build cost
make package    # Cargo verification and registered source/license archive audit
make release-gate  # the one release gate, run on the release toolchain by pull requests and release qualification

Resource profiling is available with make resources; see measurement scope and prerequisites. It uses external profilers and adds no crate runtime dependencies.

Coverage-guided campaigns for each of the ten targets are available with make fuzz TARGET=<target> (for example TARGET=json); see properties, replay, and qualification limits. The default make fuzz currently stops on the issue #11 and #6 signatures, listed under known limitations; make fuzz-hosted completes every target with those limitations retained and named.

Conformance

JSON Schema validation implements two dialects, selected by $schema: Draft 2020-12 (the default) and Draft-07 (http://json-schema.org/draft-07/schema#, with or without the #, as MCP servers commonly declare). Draft-07 support covers tuple items with additionalItems, definitions, both forms of dependencies, $ref overriding its siblings, $id base-URI changes and plain-name #anchor identifiers, and annotation-only format; Draft-07 validations report validator purrassist.schema.draft-07.v1. Draft 2019-09, draft-06, and earlier dialects are rejected at compilation. Witness generation, schema-guided recovery, and the tool-declaration adapters follow whichever of the two dialects applies.

The checked-in main Draft 2020-12 corpus contains 1,301 tests, with another 121 selected optional cases exercised, plus the complete vendored optional/format/ corpus (878 cases across every 2020-12 format, including RFC 5892/5893 IDNA2008 contextual and Bidi rules) run under a dialect declaring the format-assertion vocabulary. All 929 required Draft-07 cases pass; of 911 Draft-07 optional/ cases (formats judged by their annotation results), 905 pass, and the 6 that do not are listed by group with reasons: content assertion (annotation-only by design) and a Draft 2019-09 cross-draft reference (not an implemented dialect). Unicode 17 normalization contains 20,034 cases. These suites, regression tests, fixed helper transcripts, and bounded mutation probes run locally. Full release qualification requires the exact-commit gates and registry acceptance described in the qualification record.

License and family

First-party code is available under MIT OR Apache-2.0 OR MulanPSL-2.0, at your choice (MIT, Apache-2.0, MulanPSL-2.0). GitHub's sidebar shows only one of the three licenses; the SPDX expression in Cargo.toml is authoritative. Third-party data and grammar dependencies retain their own notices. PurRAssist shares Blackcat Informatics' cat silhouette and palette with PurRDF; the braces and validation mark are this crate's service emblem.